Protein defination,Classification,function,level structure

PROTEIN

The substance that's found in food like egg, meals. which help people for growth and  healthy is called protein.

Classification of protein

On the basis of constitution protein are three types.
1. Simple protein.
2. Conjugate protein.
3. Derived protein
·Simple protein:- Simple protein are built of one or more complete polypeptides without any additional group. They are composed solely of amino acid. They are further divided into two categories.
A. Structural protein.:- They are constituents of active protoplasm. Depending upon their function. The structural protein or 'enzymatic' & non-enzymatic.

B. Reserve or storage protein:- These protein are present as food reserve. They are globular and soluble in water. Some of them are heat sensitive also.

· Conjugated protein:- These protein contains in addition to amino acids other organic and inorganic material called prosthetic group of proteins.

Eg- HAEMOGLOBIN:- It contain iron as additional component.
GLYCOPROTEIN:- It contain carbohydrates as additional component.
LIPOPROTEIN:- It contain lipids as additional component.

· Derived protein:- They include met proteins, albuminoses, peptones, polypeptides and other products of partial hydrolysis of protein. They are intermediate products which do not accumulate.

Classification of protein.

On the basis of shape.
Fibrous protein:- They are thread-like proteins which may occur single in group s to form sheets. When they occur in groups, the polypeptide chains run parallel along a single axis. F·P are tough & insoluble in aquatic solution. They are non-enzymatic but structural proteins.

fibrous protein

Globular protein:-They are proteins in which the tightly packed polypeptide chains are coiled and abundantly folded to form sphere or globes. They may be enzymatic or non-enzymatic. They are generally soluble in aqueous solution and are capable of rapid fusion.

Function of protein.

1. They are the major constituents of protoplasm.
2. They are essential for cell division, growth,repair and reproduction.
3. Connective tissue of animals is two types of protein fibres- collagen & elastin.
4. Nucleoproteins performs an important function in controlling the working of DNA.
5. Some protein take part in the transport of substance. Example:- oxygen by haemoglobin.
6. Reserve protein provide amino acid for growth and repair eg. Albumin.
7. Some protein function as antibodies.
8. They act as buffers, since they resist the change in PH of the cells.
9. Toxin protein are used as defense by organisms eg snake venom.
10. Some protein act as hormones & regulate various activities in living organism eg Growth hormones.

Various levels of structure of protein

primary structure:-It consists of the sequence of amino acid residues joint through peptide bonds in the polypeptide of a protein the number of amino acid residues in a chain and the arrangement of amino acid are usually specific as each polypeptide is synthesized under construction from a cistron of DNA through mRNA.
Secondary structure:- It refers to the manner of extension or helical coiling of the polypeptide chain (particularly in fibrous protein). Which results mainly from hydrogen bonding between oxygen of carboxylic group of one amino acid residues and 'NH' group of next 4th amino acid residue. It is various types but  two main categories
1. Alpha helix
2. Beta-pleated sheet

Alpha helix:- Alpha helix is a secondary structure of proteins that consists of a peptide chain folded into right-handed spiral conformation & stabilized by H-bonds between C=O of one amino acid & N-H of fourth amino acid from that postion.

Beta-pleated sheet:- Beta-pleated sheet are made of Beta strands connected laterally by 2 more hydrogen bond forming a backbone twisted, pleated sheet. this structure occur when two or more segments of polypeptide chain overlap one another & and form hydrogen bond with each other.
Tertiary structure:- It refers to the folding and bending of polypeptide chain to form globular protein include buy covalent disulphide bonds (-S-S),hydrogen & Salt bonds & hydrophobic/hydrophilic interaction.
Quarternary structure:- It is found only those proteins which have two or more polypeptides. it refers to the manner in which the individual polypeptide chains fit together in a multimeric or oligomeric protein example:- in haemoglobin.