МИНИСТЕРСТВО ОБРАЗОВАНИЯ И НАУКИ РЕСПУБЛИКИ КАЗАХСТАН
ГОСУДАРСТВЕННЫЙ УНИВЕРСИТЕТ имени ШАКАРИМА города СЕМЕЙ
Документ СМК 3 уровня
УММ
УММ
042-18-25.1.55/03-2016
Учебно –методические материалы "Basis of biochemistry "
Редакция №1
от 8 сентября 2016 г.
УЧЕБНО-МЕТОДИЧЕСКИЙ КОМПЛЕКС
ДИСЦИПЛИНЫ
"Basis of biochemistry "
Для специальности
5BB080100 – Agronomy
5B080700 – Forests and forestry
5B080300 – Hunting study and fur-farming
5B080200 – Technology of production animal products
5B060800 – Ecology
5B073100 – Health and safety and protection of environment
5B120100 – Veterinary medicine
5B120200 – Veterinary Sanitation
УЧЕБНО-МЕТОДИЧЕСКИЕ МАТЕРИАЛЫ
Семей
2016
СОДЕРЖАНИЕ
1 Глоссарий 3
2 Лекции 5
3 Практические и лабораторные задания 154
4 Самостоятельная работа студента 194
5 Лист регистрации 218
1. The conceptual apparatus
"Rule of 10%" (rule of the pyramid energy R. Lindemann): from
one trophic level ecological pyramid moves to another higher its
level (the "ladder" producer - consumer), on average, about 10%
received the previous uro¬ven energy .
Abiotic factors - factors of inanimate nature (cosmic,
geophysical, climatic, spatial, temporal, etc.) that have a direct
or indirect impact on living organisms.
Act of tolerance (V.Shelford): environmental factors, with
specific conditions pessimal (unfavorable as a minimum, and excess)
value that limits the ability of the species in these conditions,
in spite of and in spite of the optimal combination of certain
other conditions.
Agrocenoses - community of organisms cultured and accompanying
them in agriculture.
Amensalizm - type of interspecies relationships, in which in a
joint environment, one kind of organism suppresses susche¬stvovanie
another species without experiencing resistance.
Anthropogenic factors - factors that have arisen as a result of
human activity.
Autotrophs - organisms can synthesize or¬ganicheskoe agent of
carbon dioxide, water and salts mine¬ralnyh. energy sources are
used for the biosynthesis of light (in photoautotrophs) or
oxidation of a number of inorganic substances (in
chemoautotrophs).
Bio-accumulation - the accumulation of substances (man-made
pollutants) in the body increasing trophic levels.
Biogen - a nutrient; nutrients, nutrients essential chemical
elements that make up the substance of living organisms, carbon,
hydrogen, oxygen, nitrogen, sulfur, phosphorus.
Boreal zone - the zone of temperate forests.
Chemosynthesis - synthesis of organic substances in
chemoautotrophic bacteria using as power sources of certain
inorganic oxidizing substances.
Co-evolution - in parallel, the joint conjugate evolution of
mankind and nature.
Consuments - heterotrophic organisms (mostly animals) who
consume organic matter other plant organisms (herbivores -
herbivores) and animals (carnivores - zoophages).
Cryostasis - temporary total suspension of the body's vital
functions associated with the onset of unfavorable conditions or
with extreme phase of individual development.
Depopulation - a reduction in population, population.
Desertification (aridity) - the process of depletion of
vegetation associated with a persistent reduction in moisture
areas, its transformation in the arid zone, topically, followed by
the previous member of the chain.
Detritophages - organisms that feed on detritus
(saprophagous).
Detritus - dead organic matter, isolation and decay organisms
products.
Disadaptation - violations of vital activity caused by the
incompleteness of acclimation, the inability to fully adapt to
changing environmental conditions.
Dissimilation - the disintegration of complex organic substances
in the body, accompanied by the release of energy, which is used in
the processes of life.
Ecological culture - system of scientific knowledge about the
human interaction of society and nature; environmental value
orientations, rules and regulations; moral and aesthetic attitude
towards nature; skills for the study of nature and its
protection.
Edafon - a set of soil animal population of the Earth's thermal
radiation air.
Education - a relatively meaningful and purposeful nurturing
person in accordance with the specific objectives of groups and
organizations, in which it is carried out.
Ektotermy - organisms, the body temperature is a little
different from the temperature of the environment and follow its
changes: lower organisms, plants, cold-blooded animals.
Emergence - the emergence of completely new properties of the
interaction of two or more objects or phenomena, properties that
are not simply the sum of the original.
Endotherm - warm-blooded animals birds and mammals, are capable
of using the internal mechanisms of thermoregulation to maintain a
relatively constant body temperature, to a certain extent
independent of the ambient temperature. "
Environmental - trudnosti crisis, environmental problems due to
anthropogenic human activities.
Environmental education - the formation of the human conscious
perception of the environment, the conviction of the need for
respect for nature, rational use of its wealth of natural
resources.
Environmental education - tselenapravlennaya specially
organized, systematic educational activities aimed at the
development of environmental education and upbringing of children,
on the formation of environmental awareness and skills for the
study of nature and its protection.
Environmental education and training of students - pedagogical
process, which ultimately should provide insight into the
importance of proper behavior in the natural environment, the
ability to anticipate and assess the impact of its activities, the
realization that the man part of nature /
Environmental upbringing - purposeful human development,
including the formation of its ecological culture, the perception
of not only the public, but also of environmental norms and
values;
Eurybionts (evrieki) - organisms that exist in a wide range of
changes in environmental conditions: temperature (evritermy),
humidity (evrigidridnye organisms), food choices (euryphages),
etc.
Eutrophication - the excessive enrichment of water with
nutrients.
Gene flow - the process of undirected random changes in gene
frequency in a population.
Heterotrophic organisms - organisms that feed on organic matter
ready.
Hibernation - a significant reduction in the level of life upon
the occurrence of adverse external conditions (for example,
hibernating animals).
Homeostasis - the ability of an organism or organisms of the
system to maintain stable dynamic equilibrium in a changing
environment.
Humid Zone - area or natural-climatic zone with high
Law of constancy of the amount of living matter of the biosphere
(Vernadsky): The number of living matter (biomass of all organisms)
for the biosphere of the geological eras.
Noogenesis (noospherogenesis) - the process of formation of the
noosphere.
optimality law: any system with the highest efficiency in the
functioning of some specific spatio-temporal limits to her.
Phenotype - a set of genetically determined characteristics and
properties of the organism.
Photoperiodism - change the state of biological systems due to
the natural rhythm of light exposure, the change of day and night,
seasonal changes in the length of daylight.
Phytocoenosis - multispecies plant community.
Phytophagy - herbivorous animals.
Phytoplankton - a set of micro-algae, small plant organisms that
live in the water column
Rule D.Allena: increase protruding body parts of one species or
closely related species of warm-blooded animals (limbs, tail, ears)
when moving from north to south.
Rule K.Bergmana: warm-blooded animals, subject to geographical
variation, the body size of individuals statistically (on average)
more than in populations living in colder parts of its range.
Security Environment - the degree of protection of the
territorial complex ecosystems, the human potential of the
eco-logical lesions derived from the magnitude of environmental
risk.
Technosphere - "technical envelope" - artificially transformed
space of the planet, being under the influence of human industrial
activity products.
The capacity of the ecosystem - the maximum size of the
population of one species, this ecosystem which is capable of
supporting in certain environmental conditions for a long time.
The law of irreversibility of evolution (L. Dollo): evolution is
irreversible; organism (population, species) can not return to
their previous state, already implemented in a number of his
ancestors.
The noosphere - the letters "thinking envelope", the scope
of reason; according to Vernadsky - a qualitatively new, higher
stage of development of the biosphere under the control of a
reasonable human activity.
The ontogenesis - the individual development of the organism;
multicellular egg from fertilization to aging and death.
Valence Environment - (tolerance limits) the characteristic type
of ability, populations exist in different
Valeology - science for the preservation and strengthening of
health, healthy lifestyles.
Zoophages - carnivorous organisms that feed on other animals or
their species (cannibalism).
Environmental education - process of mastering by students the
system of scientific knowledge about the natural environment as the
reality of human life, about the impact of industrial activity on
the environment of society, as well as the knowledge and skills of
environmental activities.
Environmental awareness -environmental knowledge (information,
conclusions and generalizations) about the natural environment and
interacting with her man, ecological thinking, feeling and
will.
Environmental science is a generic of the relation of organisms
in the environment (Haeckel), the science of organization and
functioning supraorganismal systems at various levels: the
populations of species, biocenoses (communities), ecosystems and
the biosphere.
2.Lectures
Module 1.Introduction.
Biochemistry subject
The main principles of chemical logic of a live condition. The
concept about macro- and microelements.
I. Basic Chemical Concepts
A. Atoms
1. Def.- the smallest unit of an element that can combine
chemically with other elements
Structure
a. Proton (+) charged
b. Neutron (not charged)
c. Electron (-) charged
1. Electrons exist in distinct orbital clouds
2. s, p, and d orbitals
3. Orbitals combine to form energy levels: K, L, M, N, etc
d. Protons and neutrons are the same mass and make up the
nucleus
2. Identification
a. Atomic number: number of protons
b. Atomic mass number: number of protons + neutrons
c. Atoms are organized into groups in the periodic
table
3. Isotopes
a. Two atoms with the same atomic number but different atomic
mass numbers
b. Differ only in the number of neutrons
c. Some are radioactive (radioisotopes)
B. Compounds
4. Def: a combination of two or more elements which are joined
chemically
5. Chemical bonding
a. Ionic: when an atom will either give or take an
electron from another atom
1. Cation: positive ion
2. Anion: negative ion
3. Electrostatic forces hold the atoms together
b. Covalent: when atoms share electrons
1. Forms single or multiple bonds
2. Sharing of electrons hold the atoms together
c. Hydrogen bonds: weak links between the hydrogen (+) end of
one polar molecule and the negative end of another polar
molecule
C. Acids and Bases
6. Acid: a substance which releases a H+ ion
7. Base: a substance which releases an OH- ion
8. pH scale
a. A method of determining how acidic or basic a solution is
b. Negative logarithmic scale: 0 (acidic) to 14 (basic)
(alkaline)
c. pH 7.0 is neutral (water)
9. Buffers: a substance which limits the change of pH
D. Basic chemical reactions
10. Synthesis: two or more atoms or molecules are combined
11. Decomposition: molecules are broken down into simpler
forms
12. Reduction
a. The addition of electrons to a molecule
b. Often accompanied by a gain of a hydrogen nucleus
(proton)
13. Oxidation
a. The removal of electrons from a molecule
b. Often accompanied by a loss of a proton
c. Oxidized atoms are more reactive than reduced atoms
II. Basic Biochemistry Concepts
A. Building Materials of Life
1. Inorganic compounds
2. Organic compounds
a. All contain some form of carbon
b. Biosynthesis: the manufacture of things by a living
organism
3. Carbohydrates
a. Structure
1. Contain only C, H, and O
2. Ratio of O:H is 1:2 (same as water H2O)
b. Reactions involving carbohydrates
1. Dehydration synthesis: joining two molecules by removing
water
2. Hydrolysis: splitting two molecules by adding water
c. Types
1. Monosaccharides (simple sugars)
a. 5-carbon: ribose
b. 6-carbon: C6H12O6 (Glucose, Galactose, Fructose)
2. Disaccharides
a. Two monosaccharides joined together (dehydration
synthesis)
b. Sucrose (table sugar): Glucose + Fructose
c. Maltose (malt sugar): Glucose + Glucose
d. Lactose (milk sugar): Glucose + Galactose
3. Polysaccharides
a. Starch: straight chain of glucose (food storage in
plants)
b. Glycogen: branched chain of glucose (food storage in
animals)
c. Cellulose: Zig-zag chain of glucose (non-digestible
roughage)
4. Lipids
a. Fats (triglycerides)
1. 3 fatty acid molecules + 1 glycerol joined by dehydration
synthesis
2. Saturated: no double bonds between carbons
3. Unsaturated: at least one double bond
b. Phospholipids
1. 2 fatty acids + 1 glycerol + 1 phosphate
2. Hydrophobic end (fat): water fearing (non-polar)
3. Hydrophilic end (phosphate): water loving (polar)
4. Used extensively in cell membranes
c. Sterols: multi-ringed compounds
1. Cholesterol
a. HDL: High density lipoprotein ("good" cholesterol)
b. LDL: Low density lipoprotein ("bad" cholesterol)
2. Hormones: i.e. prostaglandins, cortisone, etc
5. Proteins
a. Structure: composed of 20 basic amino acids
b. Protein synthesis
1. Two amino acids are brought together and dehydration
synthesis between the amino acids forms a peptide bond
2. Protein = polypeptide chain
3. The order of the amino acids is critical to the
function of a protein
c. Enzymes: large proteins which catalyze reactions
1. Structure
a. Active site: attachment site for substrates
b. Substrate: molecule which reacts with the enzyme and is
changed
c. Coenzyme: non-protein which helps to complete the active site
(vitamins)
2. Enzyme action
a. Enzyme & substrate bind at the active site
b. Reaction proceeds (lytic- splitting apart, synthetic -
putting together)
c. Enzyme and product(s) separate
6. Nucleic acids
a. Consist of long chains of repeating subunits
(nucleotides)
b. Nucleotide structure
1. 5-carbon sugar (ribose)
2. Phosphate group (PO4)
3. Organic nitrogen-containing base
c. DNA: Deoxyribonucleic acid
1. Used to store biological information
2. DNA base pairs
a. Guanine - Cytosine (G - C)
b. Adenine - Thymine (A - T)
3. Double-stranded helix shape formed by hydrogen bonds
d. RNA: Ribonucleic acid
1. Used as working blueprints for protein synthesis
2. RNA base pairs
a. Guanine - Cytosine (G - C)
b. Adenine - Uracil (A - U)
3. Single strand
III. Energy and its Changes
A. Kinetic energy: energy of motion
B. Potential energy: energy of position (stored energy)
C. Kinetic and potential energy are interconvertable
D. Energy in chemical reactions
1. Exothermic: reactions which release energy (heat)
2. Endothermic: reactions which require energy
3. Activation energy: energy needed to start a chemical
reaction
Module 2.Aminoacids.
Amino acids: classification, structure, stereochemistry,
physical and chemical properties and classification amino acids
forming proteins.
· Properties of the 20 amino acids that occur in peptides and
proteins are crucial to the structure and function of proteins.
· stereochemistry
· relative hydrophobicity or polarity
· hydrogen bonding properties
· ionization properties
· other chemical properties
· Condensation of 2 amino acids forms the peptide bond, the
amide linkage holding amino acid residues in peptide and protein
polymers.
· Properties of the peptide bond have major consequences in
terms of the 3-dimensional structures of proteins
There's an excellent website on amino acids being
developed here in the Department of Biochemistry and Molecular
Biophysics; parts of it are still under construction, but there are
links to various very useful parts of it here in these notes, and
indeed parts of it may be used in class.
BASICS
· Proteins are polymers of -amino acids:
· There are 20 different amino acids found in proteins and they
differ by the nature of the R group.
· Both the -amino group (amino group substituent on
the C) and the -carboxyl group (carboxyl substituent on
the C) are ionizable.
· -COOH group: a weak acid, can DONATE its proton, with a
pKa of about 2-3. What's the conjugate base form of the
carboxyl group? Which form is charged, and is it a positive or a
negative charge?
· -NH2 group: a weak base (there's an unshared pair
of electrons on the N; the neutral amino group can ACCEPT a
proton). What's the conjugate acid form of the amino group?
Which form is charged, and is it a positive or a negative
charge?
· pKas of -amino and -carboxyl groups are different
for different amino acids, and also are altered if they're the
terminal groups on a chain of amino acids, i.e., a peptide or
protein.
Predominant form in H2O is
the zwitterion: .
Stereochemistry of the amino acids
· -carbon is asymmetric (has four different substituents) except
for one amino acid, for which the R group is a hydrogen atom.
· amino acids occur as enantiomers (nonsuperimposable
complete mirror images)
· L-amino acids are the naturally occurring enantiomers
found in all proteins
· There are naturally occurring D-amino acids, but not
in proteins (found in some bacterial cell wall peptide
structures, in some peptide antibiotics, etc.) (D_L)
· Perspective formulas show stereochemistry; projection formulas
CAN be written "correctly", with convention that horizontal bonds
project out of paper and vertical bonds behind plane of paper, but
often biochemists use projection formulas casually (inaccurately),
knowing that if it's in a protein, it's always an L-amino
acid.
· Absolute configurations of D-glyceraldehyde as the reference
compound for -amino acids. D- and L- apply only to
the absolute configuration around the chiral carbon; 2
of the 20 amino acids (threonine and isoleucine) have a second
chiral center, requiring the RS system to describe their structures
accurately, but we aren't going to worry about using the RS system
here.
Which of the amino acids does NOT have a chiral center, so has
no D/L isomers?
Amino Acid Abbreviations
amino acid (or residue in protein)
3-letter abbreviation
1-letter abbreviation
Mnemonic for 1-letter abbreviation
Glycine
Gly
G
Glycine
Alanine
Ala
A
Alanine
Valine
Val
V
Valine
Leucine
Leu
L
Leucine
Isoleucine
Ile
I
Isoleucine
Proline
Pro
P
Proline
Methionine
Met
M
Methionine
Phenylalanine
Phe
F
Fenylalanine
Tryptophan
Trp
W
tWyptophan (or tWo rings)
Tyrosine
Tyr
Y
tYrosine
Serine
Ser
S
Serine
Threonine
Thr
T
Threonine
Cysteine
Cys
C
Cysteine
Aspartic Acid
Asp**
D
asparDic acid
Glutamic Acid
Glu*
E
gluEtamic acid
Asparagine
Asn**
N
asparagiNe
Glutamine
Gln*
Q
Q-tamine
Histidine
His
H
Histidine
Lysine
Lys
K
(before L)
Arginine
Arg
R
aRginine
* Glx = either acid or amide (when it isn't known which it
is)**Asx = either acid or amide (when it isn't known which it
is)
Properties of Amino Acid Side Chains
Side chains ("R groups") provide proteins with unique structural
and functional properties.Additional C atoms in R groups (after
the C) designated by successive Greek
letters: as shown in the structure of the amino acid
LYSINE (Nelson & Cox: Lehninger Principles of
Biochemistry, 3rd ed., p. 116):
Side chain classes
· The side chains of the amino acids play an essential role in
determining the properties of proteins.
There is a wide diversity in the chemical properties of amino
acid side chains, but they can be grouped into classes, sometimes
with overlapping "membership" (e.g., tyrosine is both aromatic and
hydroxyl-containing). Other classifications are also possible (for
example, the 5 classes in textbook, Fig. 5-5, discussed below).
You are expected to know all 20 amino acid structures and
their R group properties, including ionization properties (see
table below with "generic" pKa values for groups in peptides
and proteins and links to titration curves, and
the PDF of proton dissociation reactions).
Side Chain Class
Amino Acids
Aliphatic
glycine, alanine, valine, leucine, isoleucine
Cyclic
proline
Aromatic
phenylalanine, tyrosine, tryptophan
Hydroxyl-Containing
serine, threonine, tyrosine
Sulfur-Containing
cysteine, methionine
Basic
histidine, lysine, arginine
Acidic and Their Amides
aspartic acid, glutamic acid, asparagine, glutamine
· Nonpolar, aliphatic R groups
· Gly: quite water-soluble (as is Pro)
· Ala, Val , Leu and Ile:
increasing hydrophobicity with increasing number of C
atoms in hydrocarbon chain
· Pro: cyclic (--> unusual properties)
· shares many properties with the aliphatic group
· rigidity of ring plays critical role in protein structure
(more about that later)
· Met: methyl thioether (S-containing)
· quite hydrophobic
· Met's terminal methyl group important in metabolism
· Aromatic R groups
· Phe: phenyl group (linked to -CH2, so Phe =
alanine with a phenyl substituent on the methylene C)
· VERY hydrophobic.
· Trp: indole functional group on C
· electronegative atom in ring system
· not as hydrophobic as Phe
· hydrogen bonding capability (donor? acceptor? how many
hydrogen bonds?)
· Tyr: phenylalanine with aromatic OH group (phenolic
OH) = p-hydroxyphenylalanine
· ionizable (pKa around 10; loss of proton gives
phenolate anion)
· hydrogen bonding capability (donor? acceptor? how many
hydrogen bonds?)
· Tyr R group is the least hydrophobic of the 3 aromatic amino
acid side chains.
· Polar, uncharged R groups
· Ser and Thr: aliphatic OH groups, not
ionizable in pH range 1-13
· pKa values so high that under any biologically reasonable pH
conditions they're polar but not ionizable.
· hydrogen bonding capability (donor? acceptor? how many
hydrogen bonds?)
· Asn and Gln: amide functional groups
· VERY polar, but NOT ionizable
· hydrogen bonding capability (donor? acceptor? how many
hydrogen bonds?)
· Cys: thiol (also called
a sulfhydryl group) -- not very polar,
and IS ionizable
· sulfur atom makes protonated -SH group more
hydrophobic than an aliphatic OH group
· thiol DOES lose its proton in physiologically
relevant pH range (pKa about 8.5)
· generates -S- (thiolate anion is quite
hydrophilic due to the charge).
·
· Positively charged R groups (sometimes called "basic" R
groups)
· Arg: guanidino group
· VERY high pKa (~12+), so a very weak acid (stronger
base)
· carries + charge all across physiological pH
range
· resonance forms of guanidino group stabilize protonated form
(charge is delocalized)
· hydrogen bonding capability (donor? acceptor? how many
hydrogen bonds?)
· Lys: -amino group (a primary amine)
· pKa about 10
· protonated form (predominates at physiological pH)
carries + charge
· hydrogen bonding capability (donor? acceptor? how many
hydrogen bonds?)
· His: imidazole functional group (has 2 N atoms in
5-membered unsaturated ring)
· pKa about 6-6.5
· protonated form carries + charge, but at pH 7
predominant form is neutral (despite textbook's categorization
as "positively charged")
· very important player in catalytic activity of many
enzymes
· hydrogen bonding capability, and also proton
donor/acceptor
· Negatively charged R groups (sometimes called "acidic" R
groups)
· Asp and Glu: side chain carboxyl groups
· pKa values around 4
· predominant form at physiological pH = carboxylate
anion
· hydrogen bonding capability (donor? acceptor? how many
hydrogen bonds?)
Relative hydrophobicity/hydrophilicity of amino acid R
groups
· Table 12.2 : Polarity scale for amino acid residues based on
free energy changes for moving a residue from a hydrophobic
environment (dielectric constant = 2) into H2O.
· Similar trends for relative hydrophobicities in text Table 5-1
(diff. numerical scale, and not arranged in order of relative
polarity)
· Depending on how transfer experiments are done, different
absolute numbers can be obtained, but the general trends of
relative polarity are clear
· Phe, Met, Ile, Leu, Val are very hydrophobic
· Arg, Asp, Lys, Glu, Asn, Gln, and His are quite
hydrophilic
· The rest are in between -- neither very polar nor very
hydrophobic
· Reversible oxidation of 2 cysteine side chain thiols to
form cystine, or re-reduction to 2 thiols
· disulfide bonds between 2 Cys residues in a (usually
extracellular) protein
· often a critical structural feature in extracellular proteins
(stabilize folded structures, in interior of protein structure)
· When found in intracellular proteins, usually have
a functional role.
Ionization Properties of Amino Acid Functional Groups (in
PEPTIDES AND PROTEINS)
· weak conjugate acid/base groups in peptides and proteins
crucial to functions
·
only one -amino and one -carboxyl group
on a peptide or proteins (at the termini of the chain) because the
rest of the -amino and -carboxyl groups are tied up in
amide bonds holding monomers together in polymer (more later)
· side chain ionizable groups (only 7 of the 20 amino acids)
· PDF of the acid dissociation reactions for functional
groups of amino acid residues in peptides and proteins
· ionization states of side chain weak acid groups control
charges on protein
· Note: local environment in peptide or protein
determines actual pKa of that specific group, so the
ranges shown below (and the rather arbitrary "generic" values,
rounded off for simplicity) are only the usual expected
ranges for pKa values for the functional groups in peptides
and proteins; the pKa of a specific group in a specific protein can
lie significantly outside the expected range if the local
environment is unusual.
· links in table below are to titration
curves for that amino acid or functional group
Group
usual pKa range, in peptides &
proteins (approx."generic"pKa )
a-Carboxyl (terminal group of peptide or protein)
~3.0 - 4.0 (generic 3.0)
Asp, Glu (side chain carboxyl)
~4.0 - 4.5 (generic 4.0)
His (imidazole)
~6.0 - 7.4 (generic 6.5)
Cys (thiol, SH)
~8.5 - 9.0 (generic 8.5)
Tyr (phenolic OH)
~9.5 - 10.5 (generic 10.0)
a-Amino (terminal group of peptide or protein)
~8.0 - 9.0 (generic 8.0)
Lys (-amino)
~9.8 - 10.4 (generic 10.0)
Arg (guanidino)
~12.0 - 12.5 (generic 12.0)
Isoelectric point (pI)
· pI = "isoelectric pH" = "isoelectric point"
= pH at which the NET charge on a molecule
is ZERO.
· If pH < pI, net charge is positive (more + than -
charges)
· If pH > pI, net charge is negative (more - than +
charges)
· pI = the pH exactly halfway between the two pKa values
surrounding the zero net charge equivalence point on the titration
curve (examples to be analyzed in class: Gly and His)
· Fig. 5-10. Titration curve of glycine (Nelson &
Cox: Lehninger Principles of Biochemistry, 3rd ed.)
· Molecular separations based on charge properties (paper
electrophoresis of amino acids as an example)
· paper strip soaked in buffer, in contact with 2 reservoirs
with electrodes connected to a power supply
Buffer reservoir #1+(anode; anions move toward it)
O
Buffer reservoir #2_(cathode; cations move toward it)
^Ultraviolet absorbance of amino acid side chains
· Aromatic amino acids (Trp, Tyr, Phe) absorb light in
the near ultraviolet region of the spectrum (250-300 nm).
· Trp has highest molar absorptivity, followed by Tyr,
with Phe making only a small contribution.
· Disulfide bonds (between Cys residues in proteins) also absorb
in the uv range, but much less than the aromatics.
· Fig. 5-6 (Nelson & Cox, Lehninger Principles of
Biochemistry, 3rd ed.): Absorbance of ultraviolet light by aromatic
amino acids
Posttranslational modifications of amino acid side chains
· chemical modifications AFTER biosynthesis of
proteins
· occur for a few amino acid residues
in some proteins
· Some examples (see also Fig. 5-8, Nelson &
Cox: Lehninger Principles of Biochemistry, 3rd ed.)):
O-Phosphoserine
4-Hydroxyproline
5-Hydroxylysine
-carboxyglutamate
· reversible phosphorylation and dephosphorylation of Ser, Thr,
and Tyr residues very important in covalent regulation of activity
of some enzymes and many biosignalling proteins, including some
hormone receptors and transcription factors
· 4-hydroxyproline & 5-hydroxylysine important in structure
of collagen (fibrous protein in connective tissue)
· -carboxyglutamate important in a number of proteins whose
function involves Ca2+ binding, including several proteins
involved in blood clotting
Chemical Reactions of Amino Acids
· All amino acids have at least two reactive groups:
the amino and -carboxyl groups and these groups can react
with a variety of reagents. Here are two examples:
·
· A particularly interesting example is the green
fluorescent protein (GFP) from the Pacific Northwest
jellyfish Aequorea victoria, which has generated intense
interest as a marker for gene expression and localization of gene
products. The chromophore, which results from the spontaneous
cyclization and oxidation of the sequence -Ser65-Tyr66-Gly67- , is
unusual because it does not involve a non-protein chromophore, as
is usually the case for colored proteins. The chromophore is buried
in the interior of GFP.
·
The Peptide Bond
· Peptides and proteins:polymers of amino acids joined bypeptide
bonds
· amide linkages from condensation of -carboxyl
group of one amino acid with -amino group of another
amino acid
· process repeated many times --> linear chain of amino
acids, a polypeptide chain
· convention: sequence written from left to right starting
with residue with free -amino group
(the N-terminal or amino terminal amino acid residue) and
ending with the residue containing the free -carboxyl group
(the C-terminal or carboxyl terminal residue), e.g.,
NH2-Glu-Gly-Ala-Lys-COOH = EGAK
· average residue mass ~110 (average Mr of the 20 amino
acids minus Mr of H2O)
· a polypeptide chain with 100 amino acid residues would have a
Mr of about 11,000)
· small peptides (a "few" amino acid residues)
= oligopeptides
Peptide bond formation endergonic (Go' ~21 kJ/mol)
· (How would a cell make the reaction go in the direction of
condensation in an aqueous environment? no details needed here for
biochemical mechanism -- that's covered in BIOC 411)
· peptide bonds metastable in aqueous environment --
equilibrium lies far in direction of hydrolysis, but RATE of
hydrolysis very slow in absence of catalyst
· Enzymes that catalyze peptide bond hydrolysis
= peptidases or proteases, e.g., (specific
examples of proteases) your digestive proteases like trypsin and
pepsin
Ionization properties of peptides
· analyzed the same way as for free amino acids
· one -amino group
(pKa approx. 8) and one -carboxyl group
(pKa approx. 3), plus any ionizable side
chains on residues in the peptide
· To figure out approximate net charge of a peptide at a given
pH:
· make yourself notes on the sequence to keep track of what
you're doing
· add up charges on all the ionizable groups
Example: Fig. 5-14 (Nelson & Cox: Lehninger
Principles of Biochemistry, 3rd ed.): pentapeptide SGYAL =
Ser-Gly-Tyr-Ala-Leu =
Serylglycyltyrosylalanylleucine
Amino Acid Analysis
· Sequence of amino acids in a protein is dictated by the
sequence of nucleotides in the gene encoding that protein:
(from Berg, Tymoczko & Stryer, Biochemistry, 5th ed., p.
28)
· Each protein (unique sequence) has unique amino acid
composition.
· Can chemically hydrolyze (hot 6N HCl) a pure protein to
generate the free amino acids and determine its amino acid
composition chromatographically
· Because side chains of the amino acids have different
properties, can separate and quantitate all 20 amino acids using a
variety of chromatographic techniques, as illustrated below.
Peptide bond has resonance structures --> partial double bond
character
· Due to the partial double bond character of the peptide bond,
the O, C, N and H atoms are nearly planar and there is no
rotation about the peptide bond (peptide). As we shall see
later, the planarity of the these elements has important
consequences for the three dimensional structure of
proteins.
· Generally, the two C groups are in a trans configuration,
which minimizes steric interaction (cis/trans).
Modul 3. Proteins.
Primary structure of proteins. Secondary, tertiary and
quaternary structures. Chemical properties and methods of
definition of primary structure of proteins. Classification of
proteins. The role of proteins in a food.
Peptides and Protein Primary Structure
· Peptide bond formation: Note that a peptide bond is simply an
amide bond between the alpha carboxyl and amino groups of amino
acids. If we write the reacting groups in their unionized (acid and
amine) forms, then we can see the reaction takes place with the
loss of the elements of water, via an attack of the lone-pair
electrons of the amine on the carbonyl carbon of the carboxyl
group:
Now that we have looked at peptide bond formation, we next want
to look at the structure of this bond and the sequence of amino
acid residues (primary structures) of proteins. (Note that
"residue" refers to the remainder of a molecule after it is
incorporated into a polymer.)
· The peptide bond is formed with the elimination of water,
giving a planar bond between the carboxyl carbon and the amino
nitrogen. [overhead 5.8 MvH] This is due to the partial double bond
character on the amide/peptide bond as seen in the shorter bond
length (0.133 nm vs. 0.146 nm). [overhead 7-2, V&V] This bond
is nearly always trans in proteins due to steric interactions of
the amide hydrogen and oxygen, except for proline.
· Linear peptides will have free amino- and carboxy- terminal
groups. Thus they will exhibit titration curves similar to a free
amino acid, but with the pKa values shifted closer to simple
acid and amine values (there will be no charge stabilization).
· By convention the amino terminal residue is written on the
left progressing to the carboxyl terminal residue on the
right: +H3N-aa-aa-aa-aa-CO2-.
· Can determine the composition of a peptide by acid hydrolysis
and amino acid analysis.
· Can sequence proteins by specific enzyme and chemical
hydrolysis to give peptides which can then be run through
sequenators (up to about 100 aa's).
· Amino acid sequences have been used to help determine
relatedness of organisms.
3-D Structure of Proteins
Overview: Proteins are commonly large (MW > 6,000), globular
molecules serving many functions.
Proteins are complex systems - difficult to understand at a
fundamental structural level. Thus we search for patterns using
normal perceptual tools: regularity, clustering,
cleavage/separation/emptiness.
We are then able to discern alpha helices, beta sheets, beta
turns, and "random" regions. 310 helical regions show up with
computer searches. None of these is necessarily more or less random
than others, they are simply easier or more difficult for us to
perceive as ordered. They exist through our rationalization. Often
structural elements also appear to serve a functional role, thou
this is through our dissection of the molecular machine.
Look at theoretical possibilities resulting from the available
bond angles around the peptide bond system
· Most peptide bonds are trans because of reduced steric
hindrance. Most exceptions are with proline which has nearly equal
hindrance in both cis and trans [overhead 5.8 P]
· Any rotation in the peptide chain will therefore take place
around the two bonds of the alpha carbon, referred to as the phi
(f) and psi (y) bonds. There are a restricted number of angles
which these bonds can achieve (Figure 4.8) [overhead 5.9 P, V&V
7.6]. Of course the range of angles will be further reduced due to
side chains.
· If we assume hard spherical atoms with van der Waals radii, we
can determine the accessible phi (f) and psi (y) angles. This
procedure was followed by Ramachandran to produce
the Ramachandran plot, an example is seen in Figure 4.9 of
your text [overhead 6.2, MvH; 7.7 V&V].
· There are only a few regions of possible angles available to
the alpha carbon bonds as shown on this plot.
· Note that the common secondary structures, the alpha helix,
the beta strand, and the collagen triple helix all occur in these
regions.
· Of course real atoms are somewhat compressible and real bonds
can bend a little, so we might wonder how this plot stacks up to
reality. A study of the distribution of conformation angles of a
thousand amino acid residues in eight proteins as determined by
x-ray diffraction showed that most of the values do indeed fall in
the predicted regions. Most of the residues outside of these
regions are glycines, with the least restriction.
Let's go back and look at overall shape and interpret it. Look
for substructures that recur in various molecules. Perhaps we see a
globule is made of subglobules. Look closer and we see alpha
helices and beta structures. Finally we can discern aa
residues.
In order to understand and categorize their organization,
protein structure has been divided into four hierarchical levels
and a couple of sublevels:
· Primary structure (1°) : the linear order or sequence of
peptide bonded amino acid residues, beginning at the N-terminus.
(Characteristic bond type: covalent.)
· Secondary structure (2°): the steric relations of
residues nearby in the primary structure which give rise to local
regularities of conformation. These structures are maintained by
hydrogen bonds between peptide bond carbonyl oxygens and amide
hydrogens. The major secondary structural elements are the alpha
helix and the beta strand. (Characteristic bond type:
hydrogen.)
· Tertiary structure (3°): the steric relations of residues
distant in the primary sequence; the overall folding pattern of a
single covalently linked molecule. (Characteristic bond type:
hydrophobic; others: hydrogen, ion-pair, van der Waals,
disulfide.)
· Super secondary structure (motifs): defined associations
of secondary structural elements. (Characteristic bond type:
hydrogen & hydrophobic.)
· Domains: independent folding regions within a protein. The
group/pattern of secondary structures forming a Domain's tertiary
structure is called a Fold. (Characteristic bond type:
hydrophobic; others: hydrogen, ion-pair, van der Waals.)
· Quarternary structure (4°): the association of two or
more independent proteins via non-covalent forces to give a
multimeric protein. The individual peptide units of this protein
are referred to as subunits, and they may be identical or different
from one another. (Characteristic bond type: hydrophobic; others:
hydrogen, ion-pair, van der Waals.)
3-D Structure of Proteins 2
Secondary Structure
Tertiary structure (3°): the steric relations of residues
distant in the primary sequence; the overall folding pattern of a
single covalently linked molecule. (Characteristic bond type:
hydrophobic; others: hydrogen, ion-pair, van der Waals,
disulfide.)
· Super secondary structure (motifs): defined associations
of secondary structural elements. (Characteristic bond type:
hydrogen & hydrophobic.)
· Domains: independent folding regions within a protein. The
group/pattern of secondary structures forming a Domain's tertiary
structure is called a Fold. (Characteristic bond type:
hydrophobic; others: hydrogen, ion-pair, van der Waals.)
Last time looked at what is possible given the bond angles etc.
between amino acid residues. Now can look at specific
structures.
Alpha helix: (Figure 4.10, pg 90 of your text) [overhead
2.31 S, 5.15 P] The most frequent secondary structure is the
right-handed a-helix.
· In this cylinder-like structure the amino acid residues curl
around in a spring/rod-like structure.
· There is a rise/residue (movement along the axis) of 0.15 nm
and a pitch (rise/turn) of 0.54 nm.
· There are 3.6 residues per turn and 13 atoms/H-bonded "ring" -
this makes it a 3.613 helix.
· Very importantly, the H-bonds are nearly linear and therefore
of near maximum strength. The side chains of the helix stick out
from the sides.
· The stability of the helix is determined in part by the side
chains. Thus glycine allows too much rotational freedom to favor
this structure, while very large or like charged side chains can
also destabilize it.
· As you might expect a proline residue stops a helix abruptly
since proline' s angles are not accommodated in the helix.
Beta Strand: (Figure 4.15, pg 93 of your text) [overhead
5.19 P] The next secondary structural element is the beta-strand,
which is seen in the supersecondary structures called parallel and
anti-parallel beta sheets [overheads 7.16 & 17 V&V].
· The beta strand is in a sense an abstract structure, since,
unlike the a-helix, a beta-strand does not exist alone, there
is always another strand to make a sheet.
· In the older literature beta-sheets are considered secondary
structures, but they are more consistently considered super
secondary with the current nomenclature.
· Beta strands are nearly fully extended, thus they have very
little extensibility (stretch).
· Beta strands are stabilized by hydrogen bonding to adjacent
beta-strands. Thus they are stabilized by inter-strand H-bonds
whereas a-helices are stabilized by intra-strand H-bonds.
Aside: Fibrous proteins: alpha-keratin (hair etc.,
alpha-helix based) [overhead 7-11 V&V, 7-25 & 26];
stretched alpha-keratin (parallel b-pleated sheet) [overhead,
Figure 7-26].
3-D Structure of Proteins 3
Secondary Structure, cont.
Collagen strand: This is a specialized structure occurring
in only a particular family of fibrous proteins. It does not occur
in globular proteins that I am aware of.
· Collagen triple helix. Note repeating sequence of -(gly-x-y)-
where x is usually proline and y is usually hydroxyproline. (Fig
4.36) [overheads: 11-8&10, S; 4-10 to 12]
Non-repetitive secondary elements: Proteins can also have
non-repetitive secondary structures which consist of a few residues
in a turn or loop. Among these are:
· beta-turns:
· Type I turns: Fig. 4.18, left [overhead 7.22, V&V] four
amino acid residues in a 180° turn, usually H-bonded between the
carbonyl O of the first residue and the amide N of the fourth.
Proline is often the second residue. [overhead, 7-22 V&V]
· Type II turns: Fig. 4.18 [overhead 7.22, V&V] four amino
acid residues in a 180° turn, usually H-bonded between the carbonyl
O of the first residue and the amide N of the fourth. Glycine is
most frequently the third residue and proline is often the second
residue. [overhead, 7-22 V&V]
· A partial turn of a 310 helix. Short sections of this
helix often occur at the ends of alpha-helixes as transitional
elements.
Tertiary Structures
The Tertiary structure describes the overall folding
of a single covalent structure.
· Lysozyme model [overhead, model]
As the number of known protein structures increased additional
patterns became obvious within the tertiary level of structure:
Motifs & Domains.
Super Secondary structures (Motifs)
Recall the two classical structures based on the
beta-strand:
· Anti-parallel b-pleated sheet: strong, linear
H-bonds spaced adjacent, then R grp, then single, then R grp,
then adjacent etc. (Fig 4.15b) [overhead 7-17 V&V, 5.19 P]
· Parallel b-sheet: evenly spaced, but slanted
H-bonds (less stable), (Fig 4.15a) [overhead 5.19 P]
Let's next look at some of the other more common motifs found in
globular proteins (Fig 4.19 of your text):
· Hairpin - b-strand-short loop-b-strand
· b-meander - an anti-parallel beta sheet with short connecting
loops
· aa motif - two successive alpha-helixes with slightly
inclined axis to give better contact between side chains
· bab unit: alternate pattern of beta-strands and
alpha-helixes
· Greek Key
· b-sandwich
Domains
Large proteins (>200 aa's) usually fold up in smaller pieces
of 100-200 aa's called domains. Recall that we define a Domain as
an independent folding region in a protein. Often defined by clefts
in 3D structure giving globular elements connected by "hinges"
(single strand segments connecting the domains). Domains have the
advantages of speeding up the folding process (fold domains
independently, then assemble resultant folded domains - effectively
processing folding of domains in parallel). Another advantage of
domain structure is that nature can take bits of DNA specifying
particular domains with particular functions and assemble them in
new combinations to get new activities (e.g. combine an ATP binding
site and a sugar binding site to give a sugar phosphorylating
protein).
Example: IgG , domains, exons and evolution. [overheads:
IgG/proteins; 7.23 MvH]
· IgG made up of four independently synthesized proteins, 2
heavy chains with 4 domains each, and 2 light chains with 2 domains
each.
· Domain types: b-meander
[anti-parallel b-sheet], b-barrel. (Note that Motifs and
Domains often use the same nomenclature, and indeed often overlap.
Can in fact have Motif = Domain = Tertiary structure!)
· Domains correspond to exons of DNA (frequently, but not always
the case)
· The domains are all apparently related through gene
duplication in the remote past.
· The active site of IgG (2/IgG) is made up between two domains,
one from a heavy chain and one from a light chain.
· When immune system is developing individual cells express
single IgG molecules made from randomly expressed heavy and light
chains.
In a similar manner we see that many enzymes have active sites
created between two domains, often one domain binds one substrate
while the second binds a second substrate.
Its as if these proteins were designed by taking "off-the-shelf"
components, assembling them, and then over time (and generations)
tuning the combination up.
3-D Structure of Proteins 4
Domains, cont.
Note that domains will have their own tertiary structures, made
up of secondary and frequently supersecondary elements. Domains can
be categorized into four main groups:
1. All alpha
2. All beta
3. alpha/beta (have alternating alpha and beta structures, such
as in the beta-alpha-beta motif)
4. alpha + beta (local clusters of alpha and beta in same chain
with each cluster consisting of contiguous primary structure).
Groups of motifs forming the core of the tertiary structures of
domains are referred to as Folds. (p 99) Over 600 folds have
been discovered, with an expectation that about 1,000 exist. (a
bunch, but well below the infinite number possible!) Common
examples include (Fig 4.24) [overhead]:
· Parallel twisted sheet.
· Beta barrel.
· Alpha/Beta barrel.
· Parallel twisted sheet .
Folds/Motifs are often more highly conserved than sequences, and
so are used along with sequences to trace relatedness among
molecules and thus organisms. An example of conservation for a
domain is seen in Cytochrome c as shown in your text in Figure
4.21.
Quaternary Protein Structure
ternary (4°) structures (Fig. 4.25; overheads: MvH 6.26,
Fig 25): Geometrically specific associations of protein subunits;
the spatial arrangement of protein subunits.
Folding Hierarchy Overview
Rationale for quaternary: There are a variety of advantages
to large structures:
· Increasing the size of a protein allows better "fits" for
catalysis and binding - many weak bonds are needed to maintain
specific structures.
· Can bring sequential active sites of metabolic pathways into
close proximity.
· However, large peptides have some problems:
· The process of folding slows tremendously with increasing
size, thus folding individual subunits, and assembling these
subunits can greatly enhance folding efficiency.
· Get about 1 error / 103 aa residues due to the precision
of the translation of messenger RNA to protein. Thus need to keep
residue number down.
· Interacting subunits provide mechanisms for regulation.
Quaternary structures allows the assembly of large to extremely
large structures.
Protein Folding
Primary structure specifies tertiary (& therefore
quaternary) structure. This is known from in
vitro denaturation/renaturation studies of small
proteins.
· Denaturation means to unfold to non-functional state,
often achieve a "random coil" in solution,
· Renaturation means to return to the properly folded,
natural, and functional state.)
The classic study involved Ribonuclease: Reduce (break) -S-S-
bonds, denature with urea to random coil. Now can renature by
gently removing denaturant (urea) and oxidize -S-S- bonds.
[overhead 5.41, P] Enzyme activity fully recovered. X-ray
diffraction image same! Note - no gremlins, no magic, done in "test
tube."
Other small proteins, such as Myoglobin and proinsulin, fold up
spontaneously in the same manner as Ribonuclease. However, insulin
fails to fold correctly, since a peptide essential to folding has
been cleaved off.
Accesory Folding Proteins. The ribonuclease
renaturation-type experiment has not been repeated with large
proteins, which seem to require the participation of "folding
catalysts," the chaperones, to aid their folding.
Modul 4. Enzymes.
The nomenclature and classification of ferments. Frame and
catalytic properties of ferments. Temperature effect, рН,
concentration of ferment and substrate for speed of enzymatic
reactions. Regulation of activity of ferments
Enzymes are found all around us, they are found in every plant
and animal. Any living organism needs enzymes for its
functioning. All living being are controlled by chemical
reactions. Chemical reactions that are involved in growth,
blood coagulation, healing, combating disease, breathing,
digestion, reproduction, and everything else are
catalyzed by enzymes. Our body contains about 3,000 enzymes that
are constantly regenerating, repairing and protecting us.
Enzymes are powerhouses that are able to perform variety of
functions in the human body. Enzymes are wondrous chemicals of
nature. Enzymes are used in supplement form in medical arena.
Although our bodies can make most of the enzymes, our body can
wreak havoc the body's enzyme system and cause enzyme
depletion due to poor diet, illness, injury and genetics.
Enzymes Definition
Enzymes are large biomolecules that are responsible for many
chemical reactions that are necessary to sustain life. Enzyme is a
protein molecule and are biological catalysts. Enzymes increase the
rate of the reaction. Enzymes are specific, they function with only
one reactant to produce specific products. Enzymes have a
three-dimensional structure and they utilize organic molecules like
biotin and inorganic molecules like metal ions (magnesium
ions) for assistance in catalysis.
Substrate is the reactant in an enzyme catalyzed reaction. The
portion of the molecule that is responsible for catalytic action of
enzyme is the active site.
Characteristics of Enzymes
Characteristics of enzymes are as follows:
· Enzymes possess great catalytic power.
· Enzymes are highy specific.
· Enzymes show varying degree of specificities.
· Absolute specificity where the enzymes react specifically with
only one substrate.
· Stereo specificity is where the enzymes can detect the
different optical isomers and react to only one type of
isomer.
· Reaction specific enzymes, these enzymes as the name suggests
reacts to specific reactions only.
· Group specific enzymes are those that catalyze a group of
substances that contain specific substances.
· The enzyme activity can be controlled but the activity of the
catalysts can not be controlled.
· All enzymes are proteins.
· Like the proteins, enzymes can be coagulated by alcohol, heat,
concentrated acids and alkaline reagents.
· At higher temperatures the rate of the reaction is
faster.
· The rate of the reaction invovlving an enzyme is high at the
optimum temperature.
· Enzymes have an optimum pH range within which the enzymes
function is at its peak.
· If the substrate shows deviations larger than the optimum
temperature or pH, required by the enzyme to work, the enzymes do
not function such conditions.
· Increase in the concentration of the reactants, and substrate
the rate of the reaction increase until the enzyme will become
saturated with the substrate; increase in the amount of enzyme,
increases the rate of the reaction.
· Inorganic substances known as activators increase the activity
of the enzyme.
· Inhibitors are substances that decrease the activity of the
enzyme or inactivate it.
· Competitive inhibitors are substances that reversibly bind to
the active site of the enzyme, hence blocking the substrate from
binding to the enzyme.
· Incompetitive inhibitors are substances that bind to any site
of the enzyme other than the active site, making the enzyme less
active or inactive.
· Irreversible inhibitors are substances that from bonds with
enzymes making them inactive.
Enzyme Classification
The current system of nomenclature of enzymes uses the name of
the substrate or the type of the reaction involved, and ends with
"-ase". Example:'Maltase'- substrate is maltose. 'Hydrolases'-
reaction type is hydrolysis reaction.
Classification of enzymes
Enzymes are classified based on the reactions they catalyze
into 6 groups: Oxidoreductases, transferases, hydrolases,
lyases, isomearses, ligases.
Oxidoreductases - Oxidoreductase are the enzymes that
catalyze oxidation-reduction reactions. These emzymes are important
as these reactions are responsible for the production of heat and
energy.
Transferases - Transferases are the enzymes that catalyze
reactions where transfer of functional group between two substrates
takes place.
Hydrolases - Hydrolases are also known as hydrolytic
enzymes, they catalyze the hydrolysis reactions of carbohydrates,
proteins and esters.
Lyases - Lyases are enzymes that catlayze the reaction
invvolving the removal of groups from substrates by processes other
than hydrolysis by the formation of double bonds.
Isomerases - Isomerases are enzymes that catalyze the reactions
where interconversion of cis-trans isomers is involved.
Ligases - Ligases are also known as synthases, these are
the enzymes that catalyze the reactions where coupling of two
compounds is involved with the breaking of pyrophosphate bonds.
Structure of Enzymes
Enzymes are proteins, like the proteins the enzymes contain
chains of amino acids linked together. The characteristic of an
enzyme is determined by the sequence of amino acid
arrangement. When the bonds between the amino acid are weak,
they may be broken by conditions of high temperatures or high
levels of acids. When these bonds are broken, the enzymes become
nonfunctional. The enzymes that take part in the chemical reaction
do not undergo permanent changes and hence they remain unchanged to
the end of the reaction.
Enzymes are highly selective, they catalyze specific
reactions only. Enzymes have a part of a molecule where it
just has the shape where only certain kind of substrate can bind to
it, this site of activity is known as the 'active site'. The
molecules that react and bind to the enzyme is known as the
'substrate'.
Most of the enzymes consists of the protein and the non protein
part called the 'cofactor'. The proteins in the enzymes are usually
globular proteins. The protein part of the enzymes are known
'apoenzyme', while the non-protein part is known as the
cofactor. Together the apoenzyme and cofactors are known as
the 'holoenzyme'.
Cofactors may be of three types: prosthetic groups, activators
and coenzymes.
Prosthetic groups are organic groups that are permanently bound
to the enzyme. Example: Heme groups of cytochromes and bitotin
group of acetyl-CoA carboxylase.
Activators are cations- they are positively charged metal ions.
Example: Fe - cytochrome oxidase, CU - catalase, Zn -
alcohol dehydrogenase, Mg - glucose - 6 - phosphate, etc.
Coenzymes are organic molecules, usually vitamins or made from
vitamins. they are not bound permanently to the enzyme, but
they combine with the enzyme-substrate complex temporarily.
Example: FAD - Flavin Adenine Dinucleotide, FMN - Flavin
Mono Nucleotide, NAD - Nicotinamide Adenine Dinucleotide, NADP -
Nicotinamide Adenine Dinucleotide.
Function of Enzymes
Biological Functions of Enzymes:
· Enzymes perform a wide variety of functions in living
organisms.
· They are major components in signal transduction and cell
regulation, kinases and phosphatases help in this
function.
· They take part in movement with the help of the protein myosin
which aids in muscle contraction.
· Also other ATPases in the cell membrane acts as ion pumps in
active transport mechanism.
· Enzymes present in the viruses are for infecting
cell.
· Enzymes play a important role in the digestive activity of the
enzymes.
· Amylases and proteases are enzyme sthat breakdown large
molecules into absorbable molecules.
· Variuos enzymes owrk together in a order forming metabolic
pathways. Example: Glycolysis.
Industrial Application of Enzymes:
· Food Processing - Amylases enzymes from fungi and plants are
used in production of sugars from starch in making
corn-syrup.
· Catalyze enzyme is used in breakdown of starch into sugar, and
in baking fermentation process of yeast raises the dough.
· Proteases enzyme help in manufacture of biscuits in lowering
the protein level.
· Baby foods - Trypsin enzyme is used in pre-digestion of baby
foods.
· Brewing industry - Enzymes from barley are widely used in
brewing industries.
· Amylases, glucanases, proteases, betaglucanases,
arabinoxylases, amyloglucosidase, acetolactatedecarboxylases are
used in prodcution of beer industries.
· Fruit juices - Enzymes like cellulases,pectinases help are
used in clarifying fruit juices.
· Dairy Industry - Renin is used inmanufacture of cheese.
Lipases are used in ripening blue-mold cheese. Lactases breaks down
lactose to glucose and galactose.
· Meat Tenderizes - Papain is used to soften meat.
· Starch Industry - Amylases, amyloglucosidases and
glycoamylases converts starch into glucose and syrups.
· Glucose isomerases - production enhanced sweetening properties
and lowering calorific values.
· Paper industry - Enzymes like amylases, xylanases, cellulases
and liginases lower the viscosity, and removes lignin to soften
paper.
· Biofuel Industry - Enzymes like cellulases are used in
breakdown of cellulose into sugars which can be fermented.
· Biological detergent - proteases, amylases, lipases,
cellulases, asist in removal of protein stains, oily stains
and acts as fabric conditioners.
· Rubber Industry - Catalase enzyme converts latex into foam
rubber.
· Molecular Biology - Restriction enzymes, DNA ligase and
polymerases are used in genetic engineering, pharmacology,
agriculture, medicine, PCR techniques, and are also important in
forensic science.
Examples of Enzymes
A few well known examples of enzymes are as follows: Lipases,
Amylases, Maltases, Pepsin, Protease, Catalases, Maltase, Sucrase,
Pepsin, Renin, Catalases,
A few examples of foods that are rich in enzymes:
Enzymes are available in the food we eat. Foods that are canned,
or processed food like irradiation,drying, and freezing make the
foods enzyme dead. Refined foods are void of any sort of nutrition.
Food that is whole, uncooked and unpasteurized milk will provide
enough enzymes. There are two basic ways to increase enzyme intake.
First is to eat more fresh foods, cooking tends to kill enzymes.
Raw fruits and vegetables are a good source of enzymes. Fermented
food like yoghurt, intake improves body's enzyme status. The other
way to increase enzyme status of the body is by intake of enzyme
supplements.
Here is a list of foods rich in enzymes - Apples, apricots,
asparagus, avocado, banana, beans, beets, broccoli, cabbage,
carrots, celery, cherries, cucumber, figs, garlic, ginger, grapes,
green barley grass,kiwi fruit, etc.
Modul 5. Vitamins
The definition, constitution and classification of vitamins and
their role in enzymatic reactions and in exchange processes.
Vitamins are natural substances found in plants and animals and
known as Essential nutrients for human beings. The name vitamin is
obtained from "vital amines" as it was originally thought that
these substances were all amines. Human body uses these substances
to stay healthy and support its many functions. There are two types
of vitamins: water-soluble and fat-soluble.The body needs vitamins
to stay healthy and a varied diet usually gives you all the
vitamins you need. Vitamins do not provide energy (calories)
directly, but they do help regulate energy-producing processes.
With the exception of vitamin D and K, vitamins cannot be
synthesized by the human body and must be obtained from the diet.
Vitamins have to come from food because they are not manufactured
or formed by the body.
There are several roles for vitamins and trace minerals in
diseases:
· Deficiencies of vitamins and minerals may be caused by disease
states such as mal absorption;
· Deficiency and excess of vitamins and minerals can cause
disease in and of themselves (e.g., vitamin A intoxication and
liver disease);
· Vitamins and minerals in high doses may be used as drugs
(e.g., niacin for hypercholesterolemia).
Vitamins are essential for the normal growth and development of
a multi-cellular organism. The developing fetus requires certain
vitamins and minerals to be present at certain times. If there is
serious deficiency in one or more of these nutrients, a child may
develop a deficiency disease. Deficiencies of vitamins are
classified as either primary or secondary.
· Primary Deficiency: A primary deficiency occurs when you
do not get enough of the vitamin in the food you eat.
· Secondary Deficiency: A secondary deficiency may be due
to an underlying disorder that prevents or limits the absorption or
use of the vitamin.
Types of Vitamins
Vitamins, one of the most essential nutrients required by the
body and can be broadly classified into two main categories i.e.,
water-soluble vitamins and fat-soluble vitamins.
Water-Soluble VitaminsB-complex Vitamins
Eight of the water-soluble vitamins are known as the vitamin
B-complex group: thiamin (vitamin B1), riboflavin (vitamin B2),
niacin (vitamin B3), vitamin B6 (pyridoxine), folate (folic acid),
vitamin B12, biotin and pantothenic acid. The B vitamins are widely
distributed in foods,and their influence is felt in many parts of
the body. They function as coenzymes that help the body obtain
energy from food. The B vitamins are also important for normal
appetite, good vision, and healthy skin, nervous system, and red
blood cell formation.
Thiamin: Vitamin B1
What is Thiamin. Thiamin, or vitamin B1, helps to release energy
from foods, promotes normal appetite, and is important in
maintaining proper nervous system function.
Food Sources for Thiamin. Sources include peas, pork, liver, and
legumes. Most commonly, thiamin is found in whole grains and
fortified grain products such as cereal, and enriched products like
bread, pasta, rice, and tortillas. The process of enrichment adds
back nutrients that are lost when grains are processed. Among the
nutrients added during the enrichment process are thiamin (B1),
niacin (B3), riboflavin (B2), folate and iron.
Thiamin Deficiency. Under-consumption of thiamin is rare in the
United States due to wide availability of enriched grain products.
However, low calorie diets as well as diets high in refined and
processed carbohydrates may place one at risk for thiamin
deficiency. Alcoholics are especially prone to thiamin deficiency
because excess alcohol consumption often replaces food or meals.
Symptoms of thiamin deficiency include: mental confusion, muscle
weakness, wasting, water retention (edema), impaired growth, and
the disease known as beriberi. Thiamin deficiency is currently not
a problem in the United States.
Too much Thiamin. No problems with overconsumption are known for
thiamin.
Riboflavin: Vitamin B2
What is Riboflavin. Riboflavin, or vitamin B2, helps to release
energy from foods, promotes good vision, and healthy skin. It also
helps to convert the amino acid tryptophan (which makes up protein)
into niacin.
Food Sources for Riboflavin. Sources include liver, eggs, dark
green vegetables, legumes, whole and enriched grain products, and
milk. Ultraviolet light is known to destroy riboflavin, which is
why most milk is packaged in opaque containers instead of
clear.
Riboflavin Deficiency. Under consumption of riboflavin is rare
in the United States. However, it has been known to occur with
alcoholism, malignancy, hyperthyroidism, and in the elderly.
Symptoms of deficiency include cracks at the corners of the mouth,
dermatitis on nose and lips, light sensitivity, cataracts, and a
sore, red tongue.
Too much Riboflavin. No problems with overconsumption are known
for riboflavin.
Niacin: Vitamin B3, Nicotinamide, Nicotinic Acid.
What is Niacin. Niacin, or vitamin B3, is involved in energy
production, normal enzyme function, digestion, promoting normal
appetite, healthy skin, and nerves.
Food Sources for Niacin. Sources include liver, fish, poultry,
meat, peanuts, whole and enriched grain products.
Niacin Deficiency. Niacin deficiency is not a problem in the
United States. However, it is known to occur with alcoholism,
protein malnourishment, low calorie diets, and diets high in
refined carbohydrates. Pellagra is the disease state that occurs as
a result of severe niacin deficiency. Symptoms include cramps,
nausea, mental confusion, and skin problems.
Too much Niacin. Consuming large doses of niacin supplements may
cause flushed skin, rashes, or liver damage. Over consumption of
niacin is not a problem if it is obtained through food.
Vitamin B6: Pyridoxine, Pyridoxal, Pyridoxamine
What is Vitamin B6. Vitamin B6, otherwise known as pyridoxine,
pyridoxal or pyridoxamine, aids in protein metabolism and red blood
cell formation. It is also involved in the body’s production of
chemicals such as insulin and hemoglobin.
Food Sources for Vitamin B6. Sources include pork, meats, whole
grains and cereals, legumes, and green, leafy vegetables.
Vitamin B6 Deficiency. Deficiency symptoms include skin
disorders, dermatitis, cracks at corners of mouth, anemia, kidney
stones, and nausea. A vitamin B6 deficiency in infants can cause
mental confusion.
Too much Vitamin B6. Over consumption is rare, but excess doses
of vitamin B6 over time have been known to result in nerve
damage.
Folate: Folic Acid, Folacin
What is Folate. Folate, also known as folic acid or folacin,
aids in protein metabolism, promoting red blood cell formation, and
lowering the risk for neural tube birth defects. Folate may also
play a role in controlling homocysteine levels, thus reducing the
risk for coronary heart disease.
Food Sources for Folate. Sources of folate include liver,
kidney, dark green leafy vegetables, meats, fish, whole grains,
fortified grains and cereals, legumes, and citrus fruits. Not all
whole grain products are fortified with folate. Check the nutrition
label to see if folic acid has been added.
Folate Deficiency. Folate deficiency affects cell growth and
protein production, which can lead to overall impaired growth.
Deficiency symptoms also include anemia and diarrhea. A folate
deficiency in women who are pregnant or of child bearing age may
result in the delivery of a baby with neural tube defects such as
spina bifida.
Too much Folate. Over consumption of folate offers no known
benefits, and may mask B12 deficiency as well as interfere with
some medications.
Vitamin B12: Cobalamin
What is B12. Vitamin B12, also known as cobalamin, aids in the
building of genetic material, production of normal red blood cells,
and maintenance of the nervous system.
Food Sources for Vitamin B12. Vitamin B12 can only be found only
in foods of animal origin such as meats, liver, kidney, fish, eggs,
milk and milk products, oysters, shellfish. Some fortified foods
may contain vitamin B12.
Vitamin B12 Deficiency. Vitamin B12 deficiency most commonly
affects strict vegetarians (those who eat no animal products),
infants of vegan mothers, and the elderly. Symptoms of deficiency
include anemia, fatigue, neurological disorders, and degeneration
of nerves resulting in numbness and tingling. In order to prevent
vitamin B12 deficiency, a dietary supplement should be taken. Some
people develop a B12 deficiency because they cannot absorb the
vitamin through their stomach lining. This can be treated through
vitamin B12 injections.
Too much Vitamin B12. No problems with overconsumption of
vitamin B12 are known.
Biotin
What is Biotin. Biotin helps release energy from carbohydrates
and aids in the metabolism of fats, proteins and carbohydrates from
food.
Food Sources for Biotin. Sources of Biotin include liver,
kidney, egg yolk, milk, most fresh vegetables, yeast breads and
cereals. Biotin is also made by intestinal bacteria.
Biotin Deficiency. Biotin deficiency is uncommon under normal
circumstances, but symptoms include fatigue, loss of appetite,
nausea, vomiting, depression, muscle pains, heart abnormalities and
anemia.
Too much Biotin. No problems with overconsumption are known for
Biotin.
Pantothenic Acid
What is Pantothenic Acid. Pantothenic Acid is involved in energy
production, and aids in the formation of hormones and the
metabolism of fats, proteins, and carbohydrates from food.
Food Sources for Pantothenic Acid. Sources include liver,
kidney, meats, egg yolk, whole grains, and legumes. Pantothenic
Acid is also made by intestinal bacteria.
Pantothenic Acid Deficiency. Pantothenic Acid deficiency is
uncommon due to its wide availability in most foods.
Too much Pantothenic Acid. No problems with overconsumption are
known for Pantothenic Acid. Rarely, diarrhea and water retention
will occur with excessive amounts.
Vitamin C: Ascorbic Acid, AscorbateWhat is Vitamin C
The body needs vitamin C, also known as ascorbic acid or
ascorbate, to remain in proper working condition. Vitamin C
benefits the body by holding cells together through collagen
synthesis; collagen is a connective tissue that holds muscles,
bones, and other tissues together. Vitamin C also aids in wound
healing, bone and tooth formation, strengthening blood vessel
walls, improving immune system function, increasing absorption and
utilization of iron, and acting as an antioxidant.
Since our bodies cannot produce or store vitamin C, an adequate
daily intake of this nutrient is essential for optimum health.
Vitamin C works with vitamin E as an antioxidant, and plays a
crucial role in neutralizing free radicals throughout the body. An
antioxidant can be a vitamin, mineral, or a carotenoid, present in
foods, that slows the oxidation process and acts to repair damage
to cells of the body. Studies suggest that vitamin C may reduce the
risk of certain cancers, heart disease, and cataracts. Research
continues to document the degree of these effects.
Food Sources for Vitamin C. Consuming vitamin C-rich foods is
the best method to ensure an adequate intake of this vitamin. While
many common plant foods contain vitamin C, the best sources are
citrus fruits. For example, one orange, a kiwi fruit, 6 oz. of
grapefruit juice or 1/3 cup of chopped sweet red pepper each supply
enough vitamin C for one day.
Vitamin C Deficiency. Although rare in the United States, severe
vitamin C deficiency may result in the disease known as scurvy,
causing a loss of collagen strength throughout the body. Loss of
collagen results in loose teeth, bleeding and swollen gums, and
improper wound healing. More commonly, vitamin C deficiency
presents as a secondary deficiency in alcoholics, the elderly, and
in smokers.
The following conditions have been shown to increase vitamin C
requirements (Table 1):
· Environmental stress, such as air and noise pollution
· Use of certain drugs, such as oral contraceptives
· Tissue healing of wounds
· Growth (children from 0- 12 months, and pregnant women)
· Fever and infection
· Smoking.
Too Much Vitamin C. Despite being a water-soluble vitamin that
the body excretes when in excess, vitamin C overdoses have been
shown to cause kidney stones, gout, diarrhea, and rebound
scurvy.
Fat-Soluble Vitamins
The fat-soluble vitamins, A, D, E, and K, are stored in the body
for long periods of time and generally pose a greater risk for
toxicity when consumed in excess than water-soluble vitamins.
Eating a normal, well-balanced diet will not lead to toxicity in
otherwise healthy individuals. However, taking vitamin supplements
that contain megadoses of vitamins A, D, E and K may lead to
toxicity. The body only needs small amounts of any vitamin.
While diseases caused by a lack of fat-soluble vitamins are rare
in the United States, symptoms of mild deficiency can develop
without adequate amounts of vitamins in the diet. Additionally,
some health problems may decrease the absorption of fat, and in
turn, decrease the absorption of vitamins A, D, E and K. Consult a
medical professional about any potential health problems that may
interfere with vitamin absorption.
Vitamin A: RetinolWhat is Vitamin A
Vitamin A, also called retinol, has many functions in the body.
In addition to helping the eyes adjust to light changes, vitamin A
plays an important role in bone growth, tooth development,
reproduction, cell division, gene expression, and regulation of the
immune system. The skin, eyes, and mucous membranes of the mouth,
nose, throat and lungs depend on vitamin A to remain moist. Vitamin
A is also an important antioxidant that may play a role in the
prevention of certain cancers.
Food Sources for Vitamin A
Eating a wide variety of foods is the best way to ensure that
the body gets enough vitamin A. The retinol, retinal, and retinoic
acid forms of vitamin A are supplied primarily by foods of animal
origin such as dairy products, fish and liver. Some foods of plant
origin contain the antioxidant, betacarotene, which the body
converts to vitamin A. Beta-carotene, comes from fruits and
vegetables, especially those that are orange or dark green in
color. Vitamin A sources also include carrots, pumpkin, winter
squash, dark green leafy vegetables and apricots, all of which are
rich in beta-carotene.
Compared to vitamin A, it takes twice the amount of carotene
rich foods to meet the body’s vitamin A requirements, so one may
need to increase consumption of carotene containing plant
foods.
Recent studies indicate that vitamin A requirements may be
increased due to hyperthyroidism, fever, infection, cold, and
exposure to excessive amounts of sunlight. Those that consume
excess alcohol or have renal disease should also increase intake of
vitamin A.
Vitamin A Deficiency
Vitamin A deficiency in the United States is rare, but the
disease that results is known as xerophthalmia. It most commonly
occurs in developing nations usually due to malnutrition. Since
vitamin A is stored in the liver, it may take up to 2 years for
signs of deficiency to appear. Night blindness and very dry, rough
skin may indicate a lack of vitamin A. Other signs of possible
vitamin A deficiency include decreased resistance to infections,
faulty tooth development, and slower bone growth.
Too much Vitamin A
In the United States, toxic or excess levels of vitamin A are
more of a concern than deficiencies. The Tolerable Upper Intake
Level (UL) for adults is 3,000 mcg RAE (Table 2). It would be
difficult to reach this level consuming food alone, but some
multivitamin supplements contain high doses of vitamin A. If you
take a multivitamin, check the label to be sure the majority of
vitamin A provided is in the form of beta-carotene, which appears
to be safe. Symptoms of vitamin A toxicity include dry, itchy skin,
headache, nausea, and loss of appetite. Signs of severe overuse
over a short period of time include dizziness, blurred vision and
slowed growth. Vitamin A toxicity also can cause severe birth
defects and may increase the risk for hip fractures.
Vitamin DWhat is Vitamin D
Vitamin D plays a critical role in the body’s use of calcium and
phosphorous. It works by increasing the amount of calcium absorbed
from the small intestine, helping to form and maintain bones.
Vitamin D benefits the body by playing a role in immunity and
controlling cell growth. Children especially need adequate amounts
of vitamin D to develop strong bones and healthy teeth.
Food Sources for Vitamin D
The primary food sources of vitamin D are milk and other dairy
products fortified with vitamin D. Vitamin D is also found in oily
fish (e.g., herring, salmon and sardines) as well as in cod liver
oil. In addition to the vitamin D provided by food, we obtain
vitamin D through our skin which produces vitamin D in response to
sunlight.
Vitamin D Deficiency
Symptoms of vitamin D deficiency in growing children include
rickets (long, soft bowed legs) and flattening of the back of the
skull. Vitamin D deficiency in adults may result in osteomalacia
(muscle and bone weakness), and osteoporosis (loss of bone
mass).
Recently published data introduces a concern that some adults
and children may be more prone to developing vitamin D deficiency
due to an increase in sunscreen use. In addition, those that live
in inner cities, wear clothing that covers most of the skin, or
live in northern climates where little sun is seen in the winter
are also prone to vitamin D deficiency. Since most foods have very
low vitamin D levels (unless they are enriched) a deficiency may be
more likely to develop without adequate exposure to sunlight.
Adding fortified foods to the diet such as milk, and for adults
including a supplement, are effective at ensuring adequate vitamin
D intake and preventing low vitamin D levels.
Vitamin D deficiency has been associated with increased risk of
common cancers, autoimmune diseases, hypertension, and infectious
disease. In the absence of adequate sun exposure, at least 800 to
1,000 IU of vitamin D3 may be needed to reach the circulating level
required to maximize vitamin D’s benefits.
Who is at Risk — These populations may require extra
vitamin D in the form of supplements or fortified foods:
· Exclusively breast-fed infants: Human milk only provides 25 IU
of vitamin D per liter. All breast-fed and partially breast-fed
infants should be given a vitamin D supplement of 400 IU/day
· Dark Skin: Those with dark pigmented skin synthesize less
vitamin D upon exposure to sunlight compared to those with light
pigmented skin.
· Elderly: This population has a reduced ability to synthesize
vitamin D upon exposure to sunlight, and is also more likely to
stay indoors and wear sunscreen which blocks vitamin D
synthesis.
· Covered and protected skin: Those that cover all of their skin
with clothing while outside, and those that wear sunscreen with an
SPF factor of 8, block most of the synthesis of vitamin D from
sunlight.
· Disease: Fat malabsorption syndromes, inflammatory bowel
disease (IBD), and obesity are all known to result in a decreased
ability to absorb and/or use vitamin D in fat stores.
Vitamin E: Tocopherol
Vitamin E benefits the body by acting as an antioxidant, and
protecting vitamins A and C, red blood cells, and essential fatty
acids from destruction. Research from decades ago suggested that
taking antioxidant supplements, vitamin E in particular, might help
prevent heart disease and cancer. However, newer findings indicate
that people who take antioxidant and vitamin E supplements are not
better protected against heart disease and cancer than
non-supplement users. Many studies show a link between regularly
eating an antioxidant rich diet full of fruits and vegetables, and
a lower risk for heart disease, cancer, and several other diseases.
Essentially, recent research indicates that to receive the full
benefits of antioxidants and phytonutrients in the diet, one should
consume these compounds in the form of fruits and vegetables, not
as supplements.
Food Sources for Vitamin E
About 60 percent of vitamin E in the diet comes from vegetable
oil (soybean, corn, cottonseed, and safflower). This also includes
products made with vegetable oil (margarine and salad dressing).
Vitamin E sources also include fruits and vegetables, grains, nuts
(almonds and hazelnuts), seeds (sunflower) and fortified
cereals.
Vitamin E Deficiency
Vitamin E deficiency is rare. Cases of vitamin E deficiency
usually only occur in premature infants and in those unable to
absorb fats. Since vegetable oils are good sources of vitamin E,
people who excessively reduce their total dietary fat may not get
enough vitamin E.
Too much Vitamin E
The Tolerable Upper Intake Level (UL) for vitamin E is shown in
Table 2. Vitamin E obtained from food usually does not pose a risk
for toxicity. Supplemental vitamin E is not recommended due to lack
of evidence supporting any added health benefits. Megadoses of
supplemental vitamin E may pose a hazard to people taking
blood-thinning medications such as Coumadin (also known as
warfarin) and those on statin drugs.
Vitamin KWhat is Vitamin K
Vitamin K is naturally produced by the bacteria in the
intestines, and plays an essential role in normal blood clotting,
promoting bone health, and helping to produce proteins for blood,
bones, and kidneys.
Food Sources for Vitamin K
Good food sources of vitamin K are green, leafy-vegetables such
as turnip greens, spinach, cauliflower, cabbage and broccoli, and
certain vegetables oils including soybean oil, cottonseed oil,
canola oil and olive oil. Animal foods, in general, contain limited
amounts of vitamin K.
Vitamin K Deficiency
Without sufficient amounts of vitamin K, hemorrhaging can occur.
Vitamin K deficiency may appear in infants or in people who take
anticoagulants, such as Coumadin (warfarin), or antibiotic drugs.
Newborn babies lack the intestinal bacteria to produce vitamin K
and need a supplement for the first week. Those on anticoagulant
drugs (blood thinners) may become vitamin K deficient, but should
not change their vitamin K intake without consulting a physician.
People taking antibiotics may lack vitamin K temporarily because
intestinal bacteria are sometimes killed as a result of long-term
use of antibiotics. Also, people with chronic diarrhea may have
problems absorbing sufficient amounts of vitamin K through the
intestine and should consult their physician to determine if
supplementation is necessary.
Too much Vitamin K
Although no Tolerable Upper Intake Level (UL) has been
established for vitamin K, excessive amounts can cause the
breakdown of red blood cells and liver damage. People taking
blood-thinning drugs or anticoagulants should moderate their intake
of foods with vitamin K, because excess vitamin K can alter blood
clotting times. Large doses of vitamin K are not advised.
Modul 6.Carbohydrates
Classification of carbohydrates and their most important
reactions. Disaccharides and polysaccharides: lactose, maltose,
sucrose, starch, glycogen, cellulose, quinine. The role of
carbohydrates in a food.
CARBOHYDRATES
The carbohydrates, or sugars, are our third group of
biomolecules. They are characterized by having a carbonyl carbon
(aldehyde or ketone) and multiple hydroxyl groups. The smallest
sugars are thus the three carbon trioses, glyceraldehyde
(aldotriose) and dihydroxyacetone (ketotriose).
Note that sugars occur in both D and L forms. As we shall see
the natural sugars are generally D.
CARBOHYDRATES, cont.
Note that sugars occur in both D and L forms. As we shall
see the natural sugars are generally D. Let's look at the two
families, ald