Carbohydrates Slides

The Chemistry of life

• All living things are composed of and use chemicals

• More than 100,000 chemicals are used by living organism for

defencecommunicationaggressionreproduction and various other activities

• These chemicals may be organic/inorganic

• The branch of biology that deals with the study of chemistry of living things is called ‘BIOCHEMISTRY’

Four major organic molecules living things are associated with

• Carbohydrates: Polymers of sugars

• Lipids: Macromolecules constructed from fatty acids & glycerol

• Proteins: Polymers of amino acids

• Nucleic Acids: Polymers of nucleotides

• Biological polymers are formed by a common reaction known as CONDENSATION or DEHYDRATION SYNTHESIS REACTION

• Water is removed (dehydration) to form a bond between the growing polymer and the next monomer subunit.

• Large biological polymers are broken down through the reverse reaction—HYDROLYSIS

• Water (H-OH) is added to break a covalent bond between subunits in a polymer.

Dehydration Hydrolysis

CARBOHYDRATES

• A class of organic molecules

• Hydrates of carbon Cn(H20)n

Eg:C6H12O6 , (CH20)6, C6(H2O)6

• Monomers called monosaccharides or simple sugars

• No.of carbon atoms with a ‘ose’ indicates a carbohydrate

C6 (H2O)6

Glucose is an example of a hexose or simple sugar.

vs. sugars

• Simple sugars combine with each other by dehydration synthesis reaction to form complex carbohydrates.

• In this reaction, a macromolecule is formed when water is removed from smaller component parts.

• When one monomer with OH group attaches with H of other dehydration synthesis reaction results.

Disaccharides

• Two monomeric units bonded together

• Bonds are specifically called GLYCOSIDIC BONDS

• Sucrose = glucose + fructose

Held together by a Glycosidic bonds

Glycosidic Bond 1, 2 linkage

Glycosidic Bonds Link MonosaccharidesSucrose= a disaccharide made from glucose and fructose.

Lactose: A DissacharideThe glycosidic bond is a 1,4 linkage

The glycosidic bond

Polysaccharides(complex carbohydrates)

• More than 2 monomeric units joined by glycosidic linkage by dehydration synthesis reaction

• Eg: Starch(Plants), glycogen(storage form in animals)

• Breaking of these polymers to individual subunits is done by hydrolysis.

Cellulose

Cellulose

Cellulose: Another polysaccharide• Constructing the cell walls of plant cell• Humans cannot hydrolyse cellulose as they

lack cellulase• Hence, cellulose not used as energy source• However, this adds bulk/fibre to our diet• Helps in proper digestion, reduce risk of

colon cancer etc.

Function of Carbohydrates

• Storage substances of potential energy

• Sugar can be used by the cell as a component of other complex molecules such as DNA , RNA, ATP.

• Important for cell-cell recognition & communication

LIPIDS

Large non polar organic molecules

Insoluble in water

Soluble in organic solvents like ethers or acetone

Amount of oxygen is less as compared to hydrogen and carbon

Classification of Lipids

• Simple lipidsSteroidsProstaglandinCannot be hydrolyzed to get the monomeric

unit

Complex Lipids

• True fats• Phospholipids• Waxes • Can be hydrolyzed to get soaps

True Fats

HC OH

H2C

H2C OH

OH

O

HO R'

O

HO R'''

O

HO R" HC

H2C

H2C

O

O R'

O

O R'''

O

O R"

CH3(CH2)7CH CH(CH2)7CO2H

CH3(CH2)4CH CHCH2CH CH(CH2)7CO2H

CH3(CH2)10CO2HCH3(CH2)14CO2HCH3(CH2)16CO2H

LAURIC ACID

STEARIC ACIDPALMITIC ACID

OLEIC ACID

LINOLEIC ACID

Depending on the R group, these compounds have very different properties.

Glycerol Fatty Acid

Saturated Fatty acid (Animal fat)

Unsaturated Fatty acid (plant fat)

• A saturated fatty acid is fully loaded with hydrogen atoms and contain only single bonds between carbon.

• Generally found in animal tissues

• Solid at room temperature

Ex. Stearic acid (found in solid meat)

Saturated fatty acid:

Unsaturated fatty acids:

Carbon double bonded to each other in the chain at one or more positions

Generally Present in plants ( peanut oil, olive oil)

Liquid at room temperature

Example: Linoleic acid (Also an essential fatty acid for humans)*

• The occurence of double bonds in fatty acids is indicated by Greek letter ‘ω’ followed by a number indicating the location of first double bond in the molecule.

• E.g: • Oleic acid – C18:1 ω 9• Linoleic acid - C18: 2 ω 6 (Omega 6

Fatty acid)• Linolenic acid - C18: 3 ω 3 (Omega 3

fatty acid)

Synthesis of triglycerides

Glycerol + 3 fatty acids= Triglycerides

Phospholipids

• Fatty acids containing phosphates

• Major components of membranes

• Separates cell contents for external environment

Phospholipids

Some phospholipids are also known as Lecithins

Phospholipids

Lecithins

• Another class of phospholipids• Important constituent of cell membranes• Emulsification of fats (present in choclates)

Fatty acids Smaller fatty acids

Easy for the body to absorb

Steroids

• Lipid molecules with a typical interlocking ring structure

• Many of them acts as hormones • Steroid hormones are lipid soluble• Example: Cholesterol, testosterone, estradiol

etc.

Cholesterol

Found in blood associated with lipoproteins

Excessive deposits can cause Atherosclerosis

Used to synthesize bile salts and cell membranes

Used as compenents of cell membrane

Necessary for the synthesis of Vit.D

Importance of fats

• Molecules for storing energy• Energy of 1g fat = 2g sugar• Acts as a insulating layer under skin • Prevents heat loss from body (whales, seals

and walruses• Prevents damage to many organs by acting as

a cushion (Eyes and kidneys)

END OF LECTURE

Chapter 3

The Chemistry of life

Proteins

Polymers of amino acids

Amino acids - short carbon skeleton having amino (NH2)group on one end and carboxyl group on the other end.

Amino acids

Amino acid cont.

• Total of 20 different amino acids found in nature that differ in the R group and are very important to cells.

• These are the building blocks of the millions of different proteins found in living systems

• Out of these 20, 9 are called essential amino acids as these cannot be synthesized by body and needs to be supplied in diet. (Meth, val, leu,Iso,His, Phe,threo,trypto, lysine)

Amino Acids Cont..Amino acids are bound to one another by dehydration synthesis reaction

Carboxyl acid group of one will form Covalent bond with the amino group of the another amino acid by removal of water molecule

This covalent bond which joins the amino acids together is called as the peptide bond

Amino Acid Cont..

The long chain of amino acids formed is called polypeptide chain.

A specific polypeptide chain is composed of a specific sequence of amino acids bonded end to end.

Four levels of protein structure

• Primary structure• Secondary structure• Tertiary structure• Quaternary structure

Primary structure

Actual sequence of amino acids in a protein

This primary structure is encoded by various genes present in the DNA

The primary structure of a protein is linear.

Secondary Structure

• Twisted primary structure

• Hydrogen bonding stabilizes these structures

• Generally found of two types Alpha helix Beta Sheets

α-helix

• Similar to the shape of a coiled telephone cord

• The helical shape is maintained by hydrogen bonds between the amino acid side chains at different locations

• Ex. Hair

Beta sheets• Formed from two chain

lying parallel or anti parallel to each other

• Flat sheet like structure

• Hydrogen bonds are the major forces which stabilizes this structure

• Ex. Silk

Beta Pleated sheet

Tertiary structure

Coiled telephone cord coils around itself many times

• Contains both alpha and beta sheets• Both intermolecular and intramolecular

hydrogen bonds are formed• Ex. Myoglobin (Oxygen holding protein

containing 153aa)

Structure of Myoglobin

•

Quaternary structures

• Several tertiary polypeptides coil around each other

• Forms a large globular structure with different interacting polypeptide chains

• Disulphide bonds, covalent bonds and hydrogen bonds are present

• Ex: Haemoglobin, Insulin, Antibodies

Quaternary structure

Immunoglobulins

Importance of protein structure• Structure is closely related to its function• Any changes in the arrangement of amino

acids can have far-reaching effects on its function

• Ex. haemoglobin made up of 2 types of polypeptide chains - alpha and beta

• Change in one amino acid of one chain(glutamic acid replaced by valine in sixth position)---Chains folds in different pattern --Sickle cell anemia

Protein folding

• Either Helix or Beta sheet

• Improper folding may result into

Alzheimer’s disease, Bovine Spongiform encephalitis, Cruetzfeldt Jacobs disease

• All resulting from improper folding of helix or beta sheets

Reasons for Changes in protein structure

• Because of altered amino acid sequence

• Changing environmental conditions

Ex. Change in pH, ionic strength of the solution , Temperature

Protein denaturation

• Denaturation: Irreversible loss of physical and chemical properties of proteins

• Caused by excessive heating which disrupts the hydrogen bonds of the protein

• Common example: yellow portion of egg changing to white solid mass when heated

• Insulin kept in dark bottles to prevent Denaturation by light

Types of protein and functions

• Structural proteins Maintains the shape of cell and

organism Makes muscle cells, cell membrane,

tendons and blood cellsProvides rigidity and flexibility for body

movements

Regulatory proteins

• Regulates the various biochemical activities of the body

• Enzymes and hormones are regulatory proteins• Insulin (Hormone): produced by pancreas and

regulates the amount of glucose in the blood• If produced in less amount ----- Diabetes• Excess sugar eliminated form through urine

Oxytocin

• Another regulatory hormone

• Secreted by pituitary gland

• Stimulates the contraction of uterus during child birth

• Pitocin artificial homologue of Oxytocin

Nucleic acids

• Complex polymeric molecules which store and transfer information within a cell

• Constructed from basic monomeric units known as Nucleotides

• Nucleotide= sugar + phosphate+ organic nitrogenous bases

• Sugars: Ribose, Deoxyribose

Nucleic acids cont.

• Nitrogenous bases

1) Adenine

2) Guanine

3) Thymidine

4) Cytosine

5) Uracil (in case of RNA)

Nucleic acids – two typesDNA- Deoxyribonucleic acid

- deoxyribonucleotides

- Has deoxyribose sugar

- Has adenine, guanine, cytosine and thymine

- Usually double stranded

- Two strands joined by hydrogen bonds

- Adenine thymine pairing- Guanine Cytosine Pairing

• RNA-Ribonucleic acid- Ribonucleotides- Has ribose sugar- Has adenine, guanine,

cytosine and uracil- Usually single stranded- Secondary structure- Adenine uracil pairing

guanine – cytosine pairing

DNA(deoxyribonucleic acid)

• Hereditary molecule (stores all the information needed for protein synthesis)

• Molecular model proposed by Watson and Crick in 1953

• Has a double helix structure• Two strands are interwined in clock wise

direction in right hand helix

DNA Cont…

• The strand completes a turn each 34 Ao

• Each nucleotide occupies 3.4 Ao

• Thus there are 10 nucleotides per turn• Width of DNA molecule is 20 Ao

• Each step in DNA ladder made up of purine and pyrimidine pair

• No. of purines = No. of pyrimidines

DNA Structure

RNA structure

Phosphodiester bonds

RNA (Ribonucleic acid)

.

• Contains the information needed for protein synthesis

• Synthesized from DNA by a process known as transcription