PROTEINS

CONTENT•Introduction•Source•Classification•Structure•General properties •Importance of protein

SOURCE OF PROTEINSPLANT SOURCE:

grains,cereals,legumens,nuts ,seeds, fruits,roots and tubers like yams,cassava,and sweet potato.

ANIMAL SOURCE: meat,egg,fish and milk and milk

derived food

INTRODUCTIONProteins are polymers of -a amino acids

bonded by peptide linkages.Their molecular weights range from 5000 to

many millions.They occur in all living cells.They are present in muscle, skin, hair and

other tissues that make up the body’s non- bony structure.

As enzymes they catalyze biochemical reactions.

As hormones they regulate metabolic processes.

CLASSIFICATION

Proteins

chemical

molecular

Classification by chemical composition

Chemical compositio

n

simple proteins

Conjugated proteins

According to this system, proteins are divided into two classes;

1. SIMPLE PROTEINS: The simple proteins are those

which are made of chains of amino acid units only, joined by amide linkages.

Upon hydrolysis, they yield mixtures of amino acids and nothing else.

Example;AlbuminGlobulinGlutenin

2.CONJUGATED PROTEINS: These molecules are made of a simple

protein united covalently or non-covalently with a non-protein factor.

The non-protein portion is called prosthetic group or cofactor.

Examples:Glyco-proteinPhospho-proteinsChromo-proteins

CLASSIFICATION BY MOLECULAR SHAPES

Molecular shape

Fibrous proteins

Globular proteins

This shape-classification divides protein into two types depending on their molecular shape:

1. FIBROUS PROTEIN: In these proteins the poly-peptide chains

coil about one another and are held together by strong inter-chain hydrogen bond.

Thus their molecules assume the shape of large linear fibers which are used for connections, support, and the structure in living organisms.

They are insoluble in water. Examples:KeratinMyosinCollagen

2.GLOBULAR PROTEINS Their molecules are globular or roughly

spherical in shape. They are made of poly-peptide chains

coiled back and forth on themselves so as to make compact spheroid molecules.

The poly-peptide chains are held together firmly by inter chain hydrogen bonds.

Globular proteins are generally soluble in water or solution of acids, bases and salts.

The function of globular proteins is to maintain and regulate life processes in the living organism.

Examples:EnzymesInsulinHemoglobinAntibodiesCytochromes

STRUCTURE OF PROTEINS The proteins are made up of polymers of

amino acid by peptide bonding, hence its basic structure will be:

Proteins have a complex 3-dimensional structure. It is studied step by step at four different levels, rather than as a whole.

1. Primary structure2. Secondary structure3. Tertiary structure4. Quaternary structure

PRIMARY STRUCTUREThe primary structure of a protein refers to the

sequence of amino acid.The amino acid sequence in many proteins have

been determined and following observations are made:

1. A protein may contain more than one amino acid chain.

2. Sequence of amino acids in the protein chain is essentially random.

3. Small variation in the sequence of amino acid have pronounced effects on the properties of protein.

SECONDARY STRUCTUREThe secondary structure of a protein

refers to the shape in which long amino acid chains exist.

Many proteins consist of amino acid chain coiled into a spiral known as an a-helix.

The spiral is held together by hydrogen bonds between N-H and C=O groups vertically adjacent to one another in the helix.

TERTIARY STRUCTUREAn a-helix may be considered to be

a piece of rope which is free to bend twist and fold.

The tertiary structure of a protein refers to the final 3-dimensional shape that results from twisting, bending and folding of protein helix.

QUATERNARY STRUCTUREComplex proteins are often form from

two or more amino acid chains rather then a single amino acid chain.

Each chain is a complete protein with a characteristic primary, secondary and tertiary structure.

The quaternary structure refers to the way in which these amino acid chains of a complex protein are associated with each other.

GENERAL PROPERTIES Most proteins are colorless amorphous solid. They have no definite melting point. Proteins like amino acids, exists as

zwitterions. Most proteins are optically active. Proteins, like amino acid, have isoelectric

points. Proteins form colloidal dispersion in

water.They can pass through a filter paper but not through a membrane.

Proteins are easily precipitated :1. By heat2. By ethyl alcohol3. By conc. inorganic acid 4. By silver nitrate5. By picric acid or tannic acid6. By uv rays and x-rays Simple proteins can be hydrolysed with acids

(HCl),alkalies (NaOH),or enzymes to give component amino acid.

Proteins are oxidized on burning and putrification.The product include N,CO2 and water.

IMPORTANCE

PRESENTED BY:ANJALI KOTWAL,

B.PHARM,5th SEMESTER ,

SHOOLINI UNIVERSITY