Chemistry of Proteins. Definition: Proteins are organic compounds with a high molecular weight formed of carbon, oxygen, hydrogen and nitrogen and may.
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Slide 1
Chemistry of Proteins
Slide 2
Definition: Proteins are organic compounds with a high
molecular weight formed of carbon, oxygen, hydrogen and nitrogen
and may also contain sulfur, phosphorus coloring non-protein
organic groups and metal ions.Proteins are organic compounds with a
high molecular weight formed of carbon, oxygen, hydrogen and
nitrogen and may also contain sulfur, phosphorus coloring
non-protein organic groups and metal ions. They are polymers formed
of subunits called amino acids linked together by peptide
linkage.They are polymers formed of subunits called amino acids
linked together by peptide linkage.
Slide 3
Biological importance of proteins 1.Nutritional role: Provide
the body with essential amino acids, nitrogen and sulfur.
2.Catalytic role: All enzymes are proteins in nature. 3.Hormonal
role: Most of hormones and all receptors are protein in nature.
4.Defensive role: The antibodies (immunoglobulins) that play an
important role in the bodys defensive mechanisms are proteins in
nature.
Slide 4
5-Plasma proteins are responsible for most effective osmotic
pressure of the blood. This osmotic pressure plays a central role
in many processes, e.g., urine formation. Blood clotting factors
are proteins. 6-Transport role: Proteins carry lipids in the blood
forming lipoprotein complexes. Proteins also carry, hormones, e.g.,
thyroid hormones and minerals, e.g., calcium, iron and copper.
Hemoglobin (a chromo-protein) carries O2 from the lung to tissues
is a protein. 7-Structural role: Proteins are the main structural
component in bone, muscles, cyto-skeleton and cell membrane.
8-Control of gene expression: Most factors required for DNA
replication, transcription and mRNA translation are protein in
nature.
Slide 5
Amino Acids Amino acids are organic acids that contain NH2
group.Amino acids are organic acids that contain NH2 group. They
are the structural units of proteins and are obtained from them by
hydrolysis.They are the structural units of proteins and are
obtained from them by hydrolysis. The general formula of any amino
acid is as follows:The general formula of any amino acid is as
follows: All these amino acids are alpha-amino acids and the
metabolizible form of them are L-amino acids. Alpha-amino acid
means that the amino group is attached to the -carbon atom,All
these amino acids are alpha-amino acids and the metabolizible form
of them are L-amino acids. Alpha-amino acid means that the amino
group is attached to the -carbon atom,
Slide 6
Each amino acid (except proline and hydroxyproline) has a
carboxyl group (COOH), an amino group (NH2) and a characteristic
side chain (R).Each amino acid (except proline and hydroxyproline)
has a carboxyl group (COOH), an amino group (NH2) and a
characteristic side chain (R). All amino acids (except glycine) are
optically active, i.e., can rotate plane polarized light.All amino
acids (except glycine) are optically active, i.e., can rotate plane
polarized light. This is because the 4 groups attached to -carbon
are different. In glycine, the -carbon is attached to 2 hydrogen
atoms, therefore, is optically inactive.This is because the 4
groups attached to -carbon are different. In glycine, the -carbon
is attached to 2 hydrogen atoms, therefore, is optically
inactive.
Slide 7
Classification of Amino Acids Amino acids can be classified by
one of three methods:Amino acids can be classified by one of three
methods: I-Chemical classification: Based upon the number of amino
groups or carboxyl groups in the amino acid: 1.Neutral amino acids
(mono-amino, mono- carboxylic). 2.- Acidic amino acids (mono-amino,
dicarboxylic). 3.- Basic amino acids (diamino, mono-
carboxylic).
Slide 8
II-Biological classification: Based upon whether the amino
acids can be synthesized in human body or not: 1.Essential amino
acids: Not synthesized in the body and must be supplied in the
diet. 2.Non-essential amino acids: Can be synthesized in the body
and is not essential to be present in diet.
Slide 9
III-Metabolic Classification: Based upon the fate of amino acid
inside the body: 1. Glucogenic amino acids, that can be converted
to glucose. 2. Ketogenic amino acids, that can be converted to
ketone bodies. 3. Mixed function amino acids, i.e., can be
converted to both glucose and ketone bodies
Slide 10
I-Chemical classification (According to number of carboxyl and
amino groups)(According to number of carboxyl and amino groups)
Amino acids can be classified into: Amino acids can be classified
into: a) Neutral amino acids. b) Acidic amino acids. c) Basic amino
acids.
Slide 11
A) Neutral amino acids They contain one amino group and one
carboxyl group. They have 5 types: They contain one amino group and
one carboxyl group. They have 5 types: 1-Aliphatic amino acids:
e.g.,
Slide 12
2. Hydroxy amino acids: e.g., serine, threonine,.
Slide 13
3. Aromatic amino acids: e.g., phenylalanine and tyrosine.
Tyrosine is synthesized from phenyl alanine and both give
triiodothyronine and thyroxin, adrenaline and noradrenaline.
Melanin pigment and cresol,phenol in the body, e.g.,
Slide 14
4-Sulfur-containing amino acids: e.g., Cysteine gives cystine
and its SH group is very essential in activity of many proteins
particularly the active sites of enzymes.Cysteine gives cystine and
its SH group is very essential in activity of many proteins
particularly the active sites of enzymes.
Slide 15
5-Heterocyclic amino acids: e.g., Histidine gives histamine a
very important inflammatory mediator.Histidine gives histamine a
very important inflammatory mediator. Proline gives hydroxyproline
that is essential for collagen cross-linking.Proline gives
hydroxyproline that is essential for collagen cross-linking.
Tryptophan gives nicotinic acid, melatonin, serotonin and indican
in the body.Tryptophan gives nicotinic acid, melatonin, serotonin
and indican in the body.
Slide 16
B) Acidic amino acids They contain 2 carboxyl groups and one
amino group, e.g., glutamic acid and asparatic acid.They contain 2
carboxyl groups and one amino group, e.g., glutamic acid and
asparatic acid. These acidic amino acids can occur in the tissue in
the form of amides, e.g., glutamic acid glutamine and asparatic
acid asparagine.These acidic amino acids can occur in the tissue in
the form of amides, e.g., glutamic acid glutamine and asparatic
acid asparagine.
Slide 17
C) Basic amino acids They contain 2 amino groups and one
carboxyl group, e.g., Ornithine and Arginine. Ornithine does not
enter in the synthesis of proteins and is usually present in the
free form. It is synthesized from arginine. Citrulline is formed
from ornithine during urea synthesisThey contain 2 amino groups and
one carboxyl group, e.g., Ornithine and Arginine. Ornithine does
not enter in the synthesis of proteins and is usually present in
the free form. It is synthesized from arginine. Citrulline is
formed from ornithine during urea synthesis
Slide 18
Lysine and Hydroxy lysine: They participate in protein
cross-linking.
Slide 19
II-Metabolic classification II-Metabolic classification: Amino
acids may be classified intoAmino acids may be classified into
A-glucogenic amino acids, i.e., those which can be converted into
glucose, B-ketogenic amino acids, i.e., those which can be
converted into ketone bodies C-mixed amino acids, i.e., those which
can be converted into both glucose and ketone bodies.
III-Biological or Nutritional Classification: Some amino acids
can not be synthesized inside the body.Some amino acids can not be
synthesized inside the body. If these amino acids are not taken in
diet they will affect the growth and the health. Thus, amino acids
may be classified into:If these amino acids are not taken in diet
they will affect the growth and the health. Thus, amino acids may
be classified into: A- Essential amino acids: These are amino acids
that can not be synthesized in the human body and should be taken
in the diet, otherwise their deficiency will lead to a nutrition
deficiency disease that affect both growth and health.
Slide 22
B- Non essential amino acidsThe rest of amino acids can be
synthesized inside the human body and their deficiency in diet does
not affect the growth or the health. B- Non essential amino acids:
- The rest of amino acids can be synthesized inside the human body
and their deficiency in diet does not affect the growth or the
health. ValineIsoleucineThreonineTryptophanArginine
LeucineLysineMethioninePhenylalanineHistidine
Slide 23
I. Physical properties of amino acids: 1. Solubility: All amino
acids are soluble in water, diluted acids and alkalis.All amino
acids are soluble in water, diluted acids and alkalis. 2. Optical
activity : All amino acids, except glycine, are optically active,
i.e., they contain asymmetric carbon atom ( -carbon), thus they can
deviate the plane polarized light either to the right or to the
left.All amino acids, except glycine, are optically active, i.e.,
they contain asymmetric carbon atom ( -carbon), thus they can
deviate the plane polarized light either to the right or to the
left. 3. Absorption of ultraviolet light: Aromatic amino acids
(tryptophan, tyrosine and phenylalanine) can absorb ultraviolet
light.Aromatic amino acids (tryptophan, tyrosine and phenylalanine)
can absorb ultraviolet light.
Slide 24
Structure of Proteins There are 4 levels or orders of
organization of the structure protein molecule: primary, secondary,
tertiary and quaternary structures.There are 4 levels or orders of
organization of the structure protein molecule: primary, secondary,
tertiary and quaternary structures. This complication gives the
molecule its functional domain to explain its structure-function
requirements that if changes due to mutation will give non-
functional protein and, therefore, a disease.This complication
gives the molecule its functional domain to explain its
structure-function requirements that if changes due to mutation
will give non- functional protein and, therefore, a disease.
Slide 25
1. Primary structure: Primary structure is the linear form of
the polypeptide illustrating the total number, chemical nature, and
linear order of all of the amino acid residues in the polypeptide
chain or chains of a protein and position of disulfide bonds if
present.Primary structure is the linear form of the polypeptide
illustrating the total number, chemical nature, and linear order of
all of the amino acid residues in the polypeptide chain or chains
of a protein and position of disulfide bonds if present. The
peptide bonds (primary bond) are responsible for the primary
structure.The peptide bonds (primary bond) are responsible for the
primary structure.
Slide 26
2. Secondary structure: It is the fine folding of polypeptide
chain into specific regular coiled structure or irregular random
coiling held together by hydrogen, ionic and disulfide bonds.It is
the fine folding of polypeptide chain into specific regular coiled
structure or irregular random coiling held together by hydrogen,
ionic and disulfide bonds. It is due to the interaction of amino
acids located very close to each other.It is due to the interaction
of amino acids located very close to each other.
Slide 27
3. Tertiary structure 3. Tertiary structure: It is the final
three-dimensional form due to the more complicated course folding
and super-folding of the polypeptide chain in its secondary level
into globular or fibrous form of different size.It is the final
three-dimensional form due to the more complicated course folding
and super-folding of the polypeptide chain in its secondary level
into globular or fibrous form of different size. It is due to
interaction of amino acids located far apart (away from each
other).It is due to interaction of amino acids located far apart
(away from each other). It is the biologically active conformation
of the polypeptide and therefore, is the most liable to
denaturation.It is the biologically active conformation of the
polypeptide and therefore, is the most liable to denaturation. The
bond stabilizing the tertiary structure are disulfide bonds,
hydrogen bonds and ionic bondsThe bond stabilizing the tertiary
structure are disulfide bonds, hydrogen bonds and ionic bonds
Slide 28
4. Quaternary structures 4. Quaternary structures: Proteins
consist of two or more polypeptide chains in their tertiary
structure united by forces other than peptide bonds are said to
possess a quaternary structure.Proteins consist of two or more
polypeptide chains in their tertiary structure united by forces
other than peptide bonds are said to possess a quaternary
structure. Quaternary structure therefore, is the positional
relationship between individual polypeptides associating to form
one protein molecule. Quaternary structure therefore, is the
positional relationship between individual polypeptides associating
to form one protein molecule. The bonds responsible for the
quaternary structure are not disulphid or peptide bondsThe bonds
responsible for the quaternary structure are not disulphid or
peptide bonds
Slide 29
Slide 30
Classification of Proteins I. According to the biological
importance of the protein: 1) Proteins of high biological value:
These are all proteins of animal origin (with a few exceptions) and
some proteins of plant origin that contain all the 10 essential
amino acids in well balanced amounts and are easily
digestible.These are all proteins of animal origin (with a few
exceptions) and some proteins of plant origin that contain all the
10 essential amino acids in well balanced amounts and are easily
digestible. Examples of animal proteins include; milks and its
products, egg, liver, fishes, red and while meats.Examples of
animal proteins include; milks and its products, egg, liver,
fishes, red and while meats. Examples of the few plant proteins of
high biological value are lentils and broad beans.Examples of the
few plant proteins of high biological value are lentils and broad
beans.
Slide 31
2) Proteins of low biological value: These are proteins that
are deficient in one or more of the essential amino acids or
containing very little amount of one of them or are
indigestible.These are proteins that are deficient in one or more
of the essential amino acids or containing very little amount of
one of them or are indigestible. Most of plant protein are of low
biological value and a very few animal proteins are also of low
biological value such are collagen because is deficient in
tryptophan and cysteine and keratins because they are
indigestible.Most of plant protein are of low biological value and
a very few animal proteins are also of low biological value such
are collagen because is deficient in tryptophan and cysteine and
keratins because they are indigestible. This does not imply that a
person should eat only a protein of high biological value to avoid
deficiency of essential amino acids, but this can be also avoided
by eating two or more proteins of low biological value that
complete each others deficiencyThis does not imply that a person
should eat only a protein of high biological value to avoid
deficiency of essential amino acids, but this can be also avoided
by eating two or more proteins of low biological value that
complete each others deficiency.
Slide 32
II. According to the axial ratio of the protein molecule:
Studies on the shape of the protein molecule using ultramicroscope
indicates that there are two types of proteins in nature:Studies on
the shape of the protein molecule using ultramicroscope indicates
that there are two types of proteins in nature: 1. Fibrous
proteins.1. Fibrous proteins. 2. Globular proteins.2. Globular
proteins.
Slide 33
1.Fibrous proteins: They have an axial ratio of more than 10.
Axial ratio = Length/Width of the protein molecule. They are fairly
stable proteins. Examples,They have an axial ratio of more than 10.
Axial ratio = Length/Width of the protein molecule. They are fairly
stable proteins. Examples, a. Keratin proteins in hairs, wool,
skin, and most cells. In its native state, it is present in the
form of coiled polypeptide chains called -keratin. It can be
stretched by denaturation forming -keratin. b. Myosin is the major
protein of muscles. During muscle relaxation it is called - myosin
but during muscle contraction, it undergoes a change in its
structure and it becomes -myosin
Slide 34
2. Globular proteins 2. Globular proteins: Their axial ratio is
less than 10.Their axial ratio is less than 10. Their peptide
chains are folded or coiled on themselves in a very compact
manner.Their peptide chains are folded or coiled on themselves in a
very compact manner. They are less stable than fibrous proteins.
Examples are albumin, globulins, and insulinThey are less stable
than fibrous proteins. Examples are albumin, globulins, and
insulin
Slide 35
III. According to the composition of the Protein: There are 3
main groups: A) Simple proteins.A) Simple proteins. B) Conjugated
or conjugated proteins.B) Conjugated or conjugated proteins. C)
Derived proteins.C) Derived proteins.
Slide 36
A) Simple Proteins These are proteins which on hydrolysis
produce amino acids only.These are proteins which on hydrolysis
produce amino acids only. Simple proteins are subdivided according
to their physical properties, solubility, molecular weight and
amino acid composition into:Simple proteins are subdivided
according to their physical properties, solubility, molecular
weight and amino acid composition into: 1-Albumin and globulins.
2-Basic proteins (Histones & Protamines). 3-Acidic proteins
(Glutelins & Gliadins ).
4-Scleroproteins(Keratin&Collagen&Elastin)
Slide 37
AlbuminGlobulin - Soluble in water and salt solution - Soluble
in salt solution. - Coagulated by heat. - The same as albumin -They
are of high biological value: -The same as albumin. - Contain all
essential amino acids. -The same as albumin. - Easily digested.
-The same as albumin. - M.W.: 68 KDa. - M.W.: 150 KDa.
-Precipitated by full saturation with ammonium sulfate.
-Precipitated by half saturation with ammonium sulfate. -They are
present in: serum albumin,egg albumin, milk: lactalbumin. They are
present in: serum globulin, milk Lactglobulin, egg globulin. - It
functions as transporting protein for elements, vitamins, and
hormones other than keeping blood osmosis. - It functions in
transport also but its major function is being antibodies.
1-Albumin and globulins.
Slide 38
2-Basic proteins(rich in basic amino acids) A-Protamines:
Protamines are the simplest natural proteins. Their molecule is
small and contains not more than 20 amino acid residuesProtamines
are the simplest natural proteins. Their molecule is small and
contains not more than 20 amino acid residues Protamines are
present in sperms and ovaProtamines are present in sperms and ova
Protamines are water-soluble and ammonia soluble proteins,
non-coagulable.Protamines are water-soluble and ammonia soluble
proteins, non-coagulable. They also exist in combination with
nucleic acids in the nucleus. In plants, protamines are present in
pollen grains.They also exist in combination with nucleic acids in
the nucleus. In plants, protamines are present in pollen grains.
Protamines are strongly basic, due to the presence of large amount
of basic amino acids specially arginine.Protamines are strongly
basic, due to the presence of large amount of basic amino acids
specially arginine.
Slide 39
B-Histones: B-Histones: (compare to protamines) Histones are
basic proteins, which are characterized, by being soluble in water,
dilute acids, and insoluble in dilute ammonia.Histones are basic
proteins, which are characterized, by being soluble in water,
dilute acids, and insoluble in dilute ammonia. Their insolubility
in ammonia differentiates them from protamines.Their insolubility
in ammonia differentiates them from protamines. They are usually
present associated with nucleic acid and porphyrins.They are
usually present associated with nucleic acid and porphyrins. They
are not present in plants.They are not present in plants. The most
important amino acids entering in the structure of histones are
arginine, histidine and less lysine.The most important amino acids
entering in the structure of histones are arginine, histidine and
less lysine. The amount of their basic charges is less than
protamines.The amount of their basic charges is less than
protamines. Histones are present in glandular tissues as liver and
spleen. The protein globin, which enters in the formation of the
hemoglobin of blood, is similar to histones.Histones are present in
glandular tissues as liver and spleen. The protein globin, which
enters in the formation of the hemoglobin of blood, is similar to
histones.
Slide 40
3-Acidic proteins A-Gliadins or Prolamines : Gliadins are never
present in animals but only present in plant kingdom.Gliadins are
never present in animals but only present in plant kingdom. They
are present in high concentrations in cereals and have been
obtained from all grains except rice.They are present in high
concentrations in cereals and have been obtained from all grains
except rice. Gliadins are also called prolamines due to the
presence of a high percentage of the amino acids proline (10-14%)
and glutamine. The amino acid lysine is deficient in
gliadins.Gliadins are also called prolamines due to the presence of
a high percentage of the amino acids proline (10-14%) and
glutamine. The amino acid lysine is deficient in gliadins. Gliadins
are proteins, which are insoluble in water and saline, but soluble
in 70-80% alcohol due to the presence of excess proline.Gliadins
are proteins, which are insoluble in water and saline, but soluble
in 70-80% alcohol due to the presence of excess proline. The
examples of prolamines are gliadin of wheat and zein of maize.The
examples of prolamines are gliadin of wheat and zein of maize.
Slide 41
B-Glutelins: They are plant proteins.They are plant proteins.
They are soluble in diluted acids but not in water or diluted salt
solutions.They are soluble in diluted acids but not in water or
diluted salt solutions. They are very rich in glutamic acid. They
are very rich in glutamic acid. They have very large molecular
weight and are heat coagulable. They have very large molecular
weight and are heat coagulable. Examples are oryzenin of rice and
glutelin of wheat. Examples are oryzenin of rice and glutelin of
wheat.
Slide 42
4-Scleroproteins (Albuminoids) Scleroproteins are characterized
by their extreme insolubility in water, dilute acids and the most
common reagents.Scleroproteins are characterized by their extreme
insolubility in water, dilute acids and the most common reagents.
They are strong fibrous structural proteins that are rich in sulfur
containing amino acids and hence disulfide bonds.They are strong
fibrous structural proteins that are rich in sulfur containing
amino acids and hence disulfide bonds. Their main function is the
protection of the body.Their main function is the protection of the
body. Hairs, nail and connective tissues, contain scleroproteins
and are never present in plants. The main important groups of
scleroproteins are:Hairs, nail and connective tissues, contain
scleroproteins and are never present in plants. The main important
groups of scleroproteins are: 1. Elastins. 2. Collagens. 3.
Keratin
Slide 43
A-Elastins: They are present in the yellow fibers of the
connective tissues in lungs, uterine wall during pregnancy, tendons
and ligaments. Elastins are also present in the elastic tissues of
tendons and big arteries.They are present in the yellow fibers of
the connective tissues in lungs, uterine wall during pregnancy,
tendons and ligaments. Elastins are also present in the elastic
tissues of tendons and big arteries. It is rich in alanine,
leucine, valine and proline but deficient in cysteine, methionine,
lysine and histidine. It is rich in alanine, leucine, valine and
proline but deficient in cysteine, methionine, lysine and
histidine. Boiling scleroproteins with strong acids or strong
alkalis or their digestion by elastase leads to their hydrolysis to
free amino acidsBoiling scleroproteins with strong acids or strong
alkalis or their digestion by elastase leads to their hydrolysis to
free amino acids
Slide 44
B-Collagens: They are present in white fibrous connective
tissues, tendons and bones. They are present in white fibrous
connective tissues, tendons and bones. Collagen is insoluble in
water, dilute acids and alkalis. From this point of view it is
similar to elastins. Collagen is insoluble in water, dilute acids
and alkalis. From this point of view it is similar to elastins.
Collagen is resistant to peptic and trypsin digestion, but when
boiled for a long time with water, dilute acids or alkalis, it
changes to gelatin. Collagen is resistant to peptic and trypsin
digestion, but when boiled for a long time with water, dilute acids
or alkalis, it changes to gelatin. Thus, gelatin is a derived
protein obtained from the partial hydrolysis of collagen.Thus,
gelatin is a derived protein obtained from the partial hydrolysis
of collagen. Both gelatin and collagen are of little nutritive
value because they contain about 40% of the non-essential amino
acid glycine.Both gelatin and collagen are of little nutritive
value because they contain about 40% of the non-essential amino
acid glycine. Collagen is rich in glycine, proline and hydroxy
proline but low in sulfur containing amino acids, tryptophan and
cysteine Collagen is rich in glycine, proline and hydroxy proline
but low in sulfur containing amino acids, tryptophan and
cysteine
Slide 45
Gelatins: It is the product of prolonged boiling of collagen in
water.It is the product of prolonged boiling of collagen in water.
It is easily digested and has the property of forming a gel on
cooling (gel formation).It is easily digested and has the property
of forming a gel on cooling (gel formation). Gelatin is a very good
diet for patients because it is an appetizer and easily digested.
Gelatin is a very good diet for patients because it is an appetizer
and easily digested. Gelatin is deficient in certain essential
amino acids. So it is not an adequate protein diet, as it is
deficient in tryptophan and cysteine and contains very small
amounts of methionine (protein of low biological value). Gelatin is
deficient in certain essential amino acids. So it is not an
adequate protein diet, as it is deficient in tryptophan and
cysteine and contains very small amounts of methionine (protein of
low biological value).
Slide 46
C-Keratins Keratins are highly insoluble compounds. They are
insoluble in all protein solvents, and are not digestible by
proteolytic enzymes (e.g pepsin and trypsin). Keratins are
hydrolyzed by prolonged boiling with alkalis. Keratins are
hydrolyzed by prolonged boiling with alkalis. The sulfur content of
keratin is high. It is present in the form of cystine, which is
responsible for the stability and insolubility of keratins.The
sulfur content of keratin is high. It is present in the form of
cystine, which is responsible for the stability and insolubility of
keratins. Most keratins yield histidine, lysine and arginine amino
acids on hydrolysisMost keratins yield histidine, lysine and
arginine amino acids on hydrolysis
Slide 47
Keratins are present in hairs, nails and superficial layer of
the skin. Barium sulfide is one of the important substances that
dissolve keratins. For this reason this material enters in the
formation of cosmetics dealing with removal of hair.Barium sulfide
is one of the important substances that dissolve keratins. For this
reason this material enters in the formation of cosmetics dealing
with removal of hair. Keratin is a typical fibrous protein. It
consists of long peptide chains. The peptide chains may be coiled
or reset in spiral or helix types. Keratin is a typical fibrous
protein. It consists of long peptide chains. The peptide chains may
be coiled or reset in spiral or helix types.
Slide 48
B) Conjugated proteins On hydrolysis, they give amino acids and
prosthetic group (i.e., a non-protein group ).On hydrolysis, they
give amino acids and prosthetic group (i.e., a non-protein group ).
They include: They include: 1. Phosphoproteins: These are proteins
conjugated with phosphate. Phosphate is attached to OH group of
serine, tyrosine or threonine present in protein.These are proteins
conjugated with phosphate. Phosphate is attached to OH group of
serine, tyrosine or threonine present in protein. They are found
in:They are found in: a. Casein: milk protein.a. Casein: milk
protein. b. Vitellin: Egg yolk protein.b. Vitellin: Egg yolk
protein.
Slide 49
2. Lipoproteins: These are proteins conjugated with lipids
converting them into water soluble substances. Present in blood,
brain and egg. Cell membrane is of lipoprotein.These are proteins
conjugated with lipids converting them into water soluble
substances. Present in blood, brain and egg. Cell membrane is of
lipoprotein. Examples: Plasma lipoproteins: see lipid chemistry.
Examples: Plasma lipoproteins: see lipid chemistry. 3.
Glycoproteins: These are proteins conjugated with carbohydrates in
varying amounts attached as short or long chains. These are
proteins conjugated with carbohydrates in varying amounts attached
as short or long chains. Examples: Mucous secretion of
gastrointestinal tract and Glycoproteins of cell wall. Examples:
Mucous secretion of gastrointestinal tract and Glycoproteins of
cell wall.
Slide 50
4. Metalloproteins: These are proteins conjugated with metals
such as;These are proteins conjugated with metals such as; Iron:
e.g., ferritin is intracellular iron- binding protein and
Transferrin is an iron-binding transport protein in the blood.Iron:
e.g., ferritin is intracellular iron- binding protein and
Transferrin is an iron-binding transport protein in the blood.
Zinc: e.g., Insulin hormone present in crystals containing
zinc.Zinc: e.g., Insulin hormone present in crystals containing
zinc. Copper: e.g., Ceruloplasmin: is a protein present in blood.
It is responsible for the oxidation of Fe2+ ions to Fe3+
ions.Copper: e.g., Ceruloplasmin: is a protein present in blood. It
is responsible for the oxidation of Fe2+ ions to Fe3+ ions.
Slide 51
5. Chromoproteins: These are proteins conjugated with colored
pigment.These are proteins conjugated with colored pigment.
Example; Hemoglobin and cytochrome enzyme present in mitochondria
contains haem pigment, which is red in color. Example; Hemoglobin
and cytochrome enzyme present in mitochondria contains haem
pigment, which is red in color. 6. Nucleoproteins: These are
proteins (protamines or histones) conjugated with nucleic acids
(DNA or RNA). These are proteins (protamines or histones)
conjugated with nucleic acids (DNA or RNA). Examples; Chromosomes:
These are proteins conjugated with DNA. Examples; Chromosomes:
These are proteins conjugated with DNA. Ribosomes: They are
proteins conjugated with RNARibosomes: They are proteins conjugated
with RNA.
Slide 52
C) Derived Proteins They include:They include: A- Denatured
protein: e.g., coagulated albumin or globulin. B. Hydrolytic
product of protein: e.g., Protein Proteoses Peptone Polypeptide.
Protein Proteoses Peptone Polypeptide. 1-Proteoses, they are
soluble in water, not coagulable and precipitated by saturated salt
solution. 2-Peptones: are soluble in water and not coagulable by
heat, not precepitated by saturated salt solution.
Slide 53
3-Peptides: are soluble in water and salt solution, not
coagulable by heat. They are formed from 2 or more amino acids. The
amino acids in any polypeptide chain are arranged so that the first
amino acid has a free amino group (N-terminal end) and the last one
has a free carboxyl group (C-terminal end). So the tripeptide
alanine-cysteine-tryptophan is different from the tripeptide
tryptophan-cysteine- alanine.The amino acids in any polypeptide
chain are arranged so that the first amino acid has a free amino
group (N-terminal end) and the last one has a free carboxyl group
(C-terminal end). So the tripeptide alanine-cysteine-tryptophan is
different from the tripeptide tryptophan-cysteine- alanine.
Slide 54
Bonds responsible for protein structure I-Strong bonds: 1.
Peptide bonds (primary bond): A peptide bond is a covalent bond
formed by a reaction between amino group of one amino acid and a
carboxylic group of the next amino acid with the loss of H2O that
required ATP.A peptide bond is a covalent bond formed by a reaction
between amino group of one amino acid and a carboxylic group of the
next amino acid with the loss of H2O that required ATP.
Slide 55
2. Disulfide bonds (secondary bond): The disulfide bond is
formed between the SH groups of two cysteine residues within same
(intra-chain) or two different polypeptide chains (inter-chain).The
disulfide bond is formed between the SH groups of two cysteine
residues within same (intra-chain) or two different polypeptide
chains (inter-chain). It maintain secondary structure of a peptide
chain or connects two polypeptide chains together in the tertiary
structure.It maintain secondary structure of a peptide chain or
connects two polypeptide chains together in the tertiary structure.
It follows the peptide bond in strength but liable to
denaturation.It follows the peptide bond in strength but liable to
denaturation.
Slide 56
II- Weak bonds: 1. Hydrogen bondsHydrogen bond is a weak bond
formed between the hydrogen atom of NH of a peptide bond on one
peptide chain and the oxygen of C=O of another peptide bond on an
adjacent peptide chain or a loop belongs to same peptide chain. 1.
Hydrogen bonds : Hydrogen bond is a weak bond formed between the
hydrogen atom of NH of a peptide bond on one peptide chain and the
oxygen of C=O of another peptide bond on an adjacent peptide chain
or a loop belongs to same peptide chain.
Slide 57
2. Hydrophobic bonds 2. Hydrophobic bonds : The non polar side
chains of neutral amino acids tend to associate in hidden core of
protein molecule away from solvent.The non polar side chains of
neutral amino acids tend to associate in hidden core of protein
molecule away from solvent.
Slide 58
3. Electrostatic bonds 3. Electrostatic bonds : These are salt
bonds formed between oppositely charged groups in the side chains
of amino acids e.g. -amino group of lysine and the carboxyl group
of asparatic acid.These are salt bonds formed between oppositely
charged groups in the side chains of amino acids e.g. -amino group
of lysine and the carboxyl group of asparatic acid.
Slide 59
Denaturation of Proteins Definition: It is the loss of the
native form of the protein leading to disruption of its secondary,
tertiary and quaternary structure with the changes in their
physical and chemical characteristics and loss of their biological
activity. It is the loss of the native form of the protein leading
to disruption of its secondary, tertiary and quaternary structure
with the changes in their physical and chemical characteristics and
loss of their biological activity.
Slide 60
Causes of Denaturation Physical causes: As shaking (mechanical
effect), high temperature, X-rays and atomic radiations.As shaking
(mechanical effect), high temperature, X-rays and atomic
radiations. Chemical causes: As organic solvents (e.g. acetone),
strong alkalis and acids and agents that irreversibly precipitate
proteinsAs organic solvents (e.g. acetone), strong alkalis and
acids and agents that irreversibly precipitate proteins.
Slide 61
Effects of Denaturation Physical changesIncrease in viscosity,
Physical changes: Increase in viscosity, decreased solubility and
decreased decreased solubility and decreased diffusiblility.
diffusiblility. Chemical changes: leads to loss of hydrogen,
hydrophobic and electrostatic bonds but hydrophobic and
electrostatic bonds but not peptide and disulfide bonds.The result
not peptide and disulfide bonds.The result are loss of secondary,
tertiary and quaternary structures but not of the primary
structure. are loss of secondary, tertiary and quaternary
structures but not of the primary structure. Biological changes:
which include loss of enzymatic, hormonal and other biological
properties of proteins. Denatured proteins (e.g cooking), are
easily digested than native proteins.Biological changes: which
include loss of enzymatic, hormonal and other biological properties
of proteins. Denatured proteins (e.g cooking), are easily digested
than native proteins.
Slide 62
Significance and Application of denaturationSignificance and
Application of denaturation : Denatured proteins, e.g., cooked meat
are easily digested.Denatured proteins, e.g., cooked meat are
easily digested. Avoidance of denaturation is important for
biological samples used for determination of enzymatic, hormonal or
protein contents. This is done by proper sample collection and
storage because if denaturation occurs false results will be
obtained.Avoidance of denaturation is important for biological
samples used for determination of enzymatic, hormonal or protein
contents. This is done by proper sample collection and storage
because if denaturation occurs false results will be obtained.
Blood samples to be analyzed for small molecules, e.g., uric acid
and glucose are first treated with acid such as trichloroacetic
acid or phosphotungestic acid to precipitate the plasma proteins
(by denaturation).Blood samples to be analyzed for small molecules,
e.g., uric acid and glucose are first treated with acid such as
trichloroacetic acid or phosphotungestic acid to precipitate the
plasma proteins (by denaturation). Detection of albumin in urine by
heat coagulation test is based on denaturation by heat.Detection of
albumin in urine by heat coagulation test is based on denaturation
by heat. Several approaches for stoppage of bleeding and treatment
of burns is based on precipitation and denaturation of a
superficial protein layer.Several approaches for stoppage of
bleeding and treatment of burns is based on precipitation and
denaturation of a superficial protein layer.
Slide 63
Protein Separation Protein separation is based on 1)Protein
solubility 2)Size of protein molecule 3)Charge of the molecule
Methods of protein separation Chromatography.Chromatography.
Salting outSalting out Electrophoresis.Electrophoresis.
Dialysis.Dialysis. Ultracentrifugation.Ultracentrifugation.
Slide 64
1- Salting out It depends on elemination of water from the
solution. e.g. albumin by full saturation with Amm. sulphate
globulin by half saturation with Amm. Sulphate globulin by half
saturation with Amm. Sulphate2-Chromatography Chromatography is a
group of separation techniques, where a mixture of molecules is
separated. The separated molecules are divided between a stationary
sold phase and liquid mobile phase.The separated molecules are
divided between a stationary sold phase and liquid mobile phase.
The separation process depends on the tendency of one type of
molecules in the mixture to associate more strongly with one phase
than the other.The separation process depends on the tendency of
one type of molecules in the mixture to associate more strongly
with one phase than the other.
Slide 65
3- Electrophoresis It is movement of charged particles in an
electric field towards the oppositely charged electrode.It is
movement of charged particles in an electric field towards the
oppositely charged electrode. By electrophoresis a mixture of amino
acids, polypeptides or proteins can be separated into distinct
bands by using electric current.By electrophoresis a mixture of
amino acids, polypeptides or proteins can be separated into
distinct bands by using electric current.
Slide 66
4-Dialysis Dialysis means separation of colloids from
crystalloids. Proteins have a high molecular weight that forms a
colloidal solution.Dialysis means separation of colloids from
crystalloids. Proteins have a high molecular weight that forms a
colloidal solution. If there is a mixture of proteins (colloids)
and salts (crystalloids) they can be separated by dialysis, i.e.,
by using a semi-permeable membrane. Crystalloids with very small
molecular weight can pass through this membrane, while colloids can
not due to the large size of their particIf there is a mixture of
proteins (colloids) and salts (crystalloids) they can be separated
by dialysis, i.e., by using a semi-permeable membrane. Crystalloids
with very small molecular weight can pass through this membrane,
while colloids can not due to the large size of their partic
Slide 67
5-Ultracentrifugation: Using high speed centrifuge, a mixture
of proteins is separated into different fractions according to
their densities.Using high speed centrifuge, a mixture of proteins
is separated into different fractions according to their densities.
Lipoproteins can be separated by ultracenrifugation to
chylomicrons, VLDL, LDL, and HDL.