Proteins and denaturation of proteins

Proteins are the polypeptides. They are the long chain polymer of alpha amino acids. Proteins undergo hydrolysis to give alpha amino acids. Proteins are present in muscles, skin, hair, and other tissue that make up the body's non body structure.

Animal proteins: Meat,fish, eggs, milk, cheese, etc.

Vegetable proteins: Pulses, nuts, bean, wheat, fruits, vegetables, etc.

Proteins are nitrogenous organic compounds of high molecular weights synthesized by plants and animals which on hydrolysis by enzymes give amino acids. Their molecular weights range from 6,000 to 1,000,000. Chemically, proteins are polymeric amides, derived from alpha amino acids.
On the basis of molecular structure, proteins are broadly classified into two categories.
a) Fibrous proteins

b) Globular proteins

Fibrous proteins have either long, coiled threadlike structure or sheet type structure. They are usually insoluble in water. Hair, hoofs, skin, nails, silk, animal tissues and wool are the examples of fibrous proteins.

The globular proteins, on the other hand, have their coils looped, twisted and folded so as to have a sphere like compacts structure. Globular proteins are soluble in water and dilute aqueous solutions of acids, bases and salts. Examples of globular proteins are the white of raw egg, blood serum, haemoglobin. Enzymes are also globular proteins.

Functions of proteins
The important role played by proteins in living cells are as follows.

i) As enzymes, they catalyze biological reactions.
ii) As hormones, they regulate metabolic processes.
iii) They serves as the chief structural material of animal tissues.
iv) In the form of antibodies, some proteins have protective and defensive function.
v) Some proteins serve as transport agents to carry oxygen, metals, fatty acids,hormones in the body, eg: Haemoglobin transports oxygen from lungs to all the parts of the bodies.
vi) Proteins act as a source of amino acid in a growing embryo.

Denaturation of proteins

The most stable state of a protein is called its native state or native form.Under certain conditions the arrangement of polypeptide chains within a protein molecule is changed from native form to a disordered arrangement.

The process which leads to the changes in the physical and biological properties of proteins without affecting its chemical composition is called denaturation of proteins.

Kauzmann, in 1959 proposed the term denaturation of protein. Thus during denaturation, only primary structure of the protein is retained. Physical and chemical properties of such proteins are different than the native proteins and they lose most of their biological activities. During denaturation, the soluble globular proteins are changed into insoluble fibrous proteins.
There are several chemicals which can denature the proteins. Minerals acids and alkalis, acetone, alcohols, salts, such as ammonium sulphate , urea, picric and trichloro acetic acids are common denaturing chemicals. Hydrostatic pressure, ultraviolet and ionizing radiations also cause denaturation.
The most common examples of the denaturation of proteins are:
i) Boiling of egg.
Boiling of an egg involves coagulation of the albumin present in the white of egg.
When an egg is boiled in water, the soluble globular proteins in the white of egg get converted into insoluble fibrous proteins.
ii) Preparation of cheese from milk.
When milk is heated with an acid (lemon juice) formation of cheese takes place. During this denaturation, the globular milk protein, lacto albumin becomes fibrous.