• The name was suggested by Berzelius
  • This name is derived from Greek Proteins means ‘first rank’
  •  Proteins are polymer of amino acids.
  •  Each amino acid is linked with another one by peptide -C=O-NH2 bond.

Different structural levels:

Primary structure

It is the linear arrangement of amino acids.


Secondary structure-

1.It is the structure found by linear Polypeptide chain which folds in a regular fashion.

2. This may be of two kinds

(1) alpha helix

(2) beta pleated sheet.

3.These secondary structures are produced by interaction between neighboring amino acids of same chain.

Quaternary structure:

The structure produced by association of more than one polypeptide.  Examples for some commonly occurring proteins.


Structural proteins :

o Collagen: Muscle protein
o Keratin: In hair and wool and nail
o Fibroin: In silk
o Elastin: Found in insect wings
o Regulatory proteins : Enzymes
o Transport proteins : Myoglobin, Haemoglobins


Another classification of proteins:

  • Simple proteins – Contains only ordinary amino acids
  • Conjugated proteins – Proteins that contain non amino acid

Components in addition to amino acids these additional factors are called prosthetic groups.

o Nucleic proteins – Nucleic acid and protein – chromosomes
o Glycoprotein – Protein and sugar units
o Lipoproteins –Protein and lipids
o Metalloproteins – metals and proteins haemoglobin

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