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Study Material

Proteins ,Structure Of Protein And Denaturation of Proteins

Proteins:

Proteins are highly complex, a natural compound composed of a large number of different amino acids.

Protein is the basis of structure and function of life.
It is a complex nitrogenous organic compound found in the protoplasm.
Animals have relatively more protein than plants.
Proteins are hydrophilic high polymer colloids.
All proteins are optically active because of the presence of the of chiral centres at alpha position of the amino acid residue.

Structure of protein:

1)Primary structure:

It refers to the linear sequence of amino acids in a protein molecule.
A proteins primary structure determines the type of function to be carried out.

2)Secondary Structure:

It deals with the shape of the individual polypeptide chains present in a protein molecule.
Secondary structure of protein molecules involves alpha -helices and beta sheets.
In alpha-helix, a single amino acid chain is coiled spirally by establishing hydrogen bonds between the first and fourth amino acids.
In the beta-pleated arrangement, a sheet is produced by holding of two or more polypeptide chains in a parallel or antiparallel manner.

3)Tertiary Structure:

When the polypeptide chains of protein molecules bend and fold to assume a more compact three-dimensional shape, a tertiary level of structure is formed.
Tertiary structure is due to a variety of bonds and interactions between amino acids side chains like disulphide bonds, electrostatic bonds, hydrogen bonds, van der Waal's interaction and hydrophobic effect.

4)Quaternary structure:

Quaternary structure of a protein is interrelation between polypeptide chains having more peptide chains.

Denaturation of Proteins:

On heating, exposing to ultraviolet radiations or treating with several solvents or reagents the proteins are denatured. These changes may be reversible or irreversible and are referred to as denaturation.
Denaturation occurs most readily near the isoelectric point.
The denatured proteins samples may contain an intact primary structure, and their three-dimensional structure is destroyed.
Reversal of denaturation is called Renaturation or Re-folding.
Boiling of an egg is an example of irreversible denaturation.
Chemical change of globular protein into fibrous protein takes place.

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