· Protein name is derived from Greek word proteios means pre-eminent or first.
· This name was suggested by a Swedish chemist Berzelius.
· Proteins are macromolecule which make up half the total weight of biomolecule in a cell.
· Proteins are also known as building blocks of life which are composed of some smaller units known as amino acid.
Structure of protein
Proteins are made up of monomers called amino acid. There are 20 different kinds of amino acid found in nature and 21st amino acid is Selenocysteine. Amino acids are basically composed of four components:
i. A central carbon with one hydrogen
ii. One carboxyl group
iii. One amino group
iv. One R group
Carbon needs four bonds in which R group is anonymous i.e. R group may be hydrogen or a hydrocarbon chain. R group can be polar, non- polar or even charged.
Amino acids bind to each other by dehydration process in which water is removed as a byproduct where OH group of one amino acid(COOH) combines with H of second amino acid(NH2) resulting in the formation of covalent(peptide) bond.
When many amino acids bind together they form a polypeptide chain.
Proteins have four level of structure. Such are as follows:
i. Primary structure
ii. Secondary structure
iii. Tertiary structure
iv. Quaternary structure
i. Primary structure: In primary structure a long string or a linear sequence of amino acid are found.
ii. Secondary structure: It is arise when intermolecular forces especially H-bonds between amine and carboxyl group of amino acid cause primary sequence to bend or twist. Secondary structure also characterized into two types:
a) Alpha helix: When secondary structure is found in the form of twists, it is called alpha helix.
b) Beta-Pleated sheets: When a bend is found in the structure, it is called β-pleated sheets.
iii. Tertiary structure: When primary and secondary bend and fold upon themselves, they give rise to tertiary structure. This is caused by the intermolecular forces (hydrophobic interaction or H-bonding), ionic bonding and covalent disulphide bridge.
iv. Quaternary structure: Some proteins join together in order to carry out their function. They results once all the interacting subunits of proteins have clumped together. Here multiple polypeptides interact with each other to fold.
Eg: Collagen, Haemoglobin
Characterstics of Protein:
i. Proteins are organic substance made up of carbon, hydrogen, oxygen, nitrogen.
ii. Proteins are the fundamental constituent of cytoplasm of cell.
iii. They are structural elements of body tissues.
iv. Proteins are polymers which are made up of monomer amino acid.
v. Their molecular weight is 5-300KD.
Classification of protein
Proteins are classified according to their shape:
a) Globular or corpuscular protein: They are compactly folded protein possess relatively spherical shape.
Eg: Insulin, Albumin, Globulin
b) Fibrous protein: When proteins resemble ribbons or fibres in shape, they are called fibrous protein.
Eg: Collagen, Keratin
Function of protein:
i. Proteins are enzymes. They function as a catalyst for example Ribonuclease which accelerate specific chemical reaction upto many times faster than they would spontaneously occur.
ii. They also function as structural materials like Keratin protein found in hairs and nails and Collagen found in connective tissue.
iii. Proteins are antibodies which have specific binding that specifically bind to foreign substance which fight against diseases and protect our body.
iv. They also serve as a specific carrier including membrane transport protein that move substance across cell membranes. Blood protein Haemoglobin(Hb) carry oxygen and transport it to blood.
v. Proteins also aid in contraction (actin,myosin) fibres that interact in muscle tissue.
vi. Proteins also involve in signaling like insulin which regulate blood glucose level.
Lipids are most diverse biological molecule which is insoluble in water and soluble in polar solvents. There are three types of lipid; simple lipid, compound lipid, derived lipid. Simple lipids includes fats and waxes. Compound lipid includes phospholipid, glycolipid. Derived lipid includes steroid, terpenes, carotenoids.
Biomolecules are organic molecule present in living organisms.They are of four types carbohydrate, protein, lipid, nucleic acid. Carbohydrates are polyhydroxy aldehydes and ketones which are classified in three types; Monosaccharides, disaccharides and polysaccharides.
Each and every enzymes are specific to catalyze a particular reaction. Enzymes are also inhibited by different kinds of inhibitors. All enzymes performs variety of functions.
Enzymes are biological catalysts which increase the rate of reaction without even participated in the reaction. Enzymes are classified into six classes.