Structure of Protein। Secondary structure of protein

Structure of protein

Protein, the significant component of food is the subject of discussion of this article. Here the article will cover structure of protein and the topic as mentioned below

  • Brief description of protein
  • Primary structure
  • Secondary structure
  • Tertiary structure
  • Quaternary structure
  • Difference between alpha helix and beta pleated sheets
  • Bonds that stabilize protein structure
1: Primary structure
2: Secondary struture
3: Tertiary struture
4: Quaternary struture

Primary structure

It is defined as the linear sequence of amino acid residue making up its polypeptide chains. The primary structure is held together by peptide bonds or peptide linkage but no other bonds or forces are involved in the primary structure of protein molecules.

The two ends of the polypeptide chain are referred to as the carboxyl terminus (C- terminus) and the amino terminus (N-terminus) based on the nature of the free group on each extremity.

Secondary structure of protein:

It consists of the three-dimensional conformation of the protein in aqueous body fluids. It conceals many nonpolar amino acid side chains in the core of coils and folds. Two main type of secondary structure are the Alpha helix and beta pleated sheets. This secondary structures are held together by hydrogen bonds.

Example of Alpha helix is keratin, collagen

Tertiary structure of protein:

Tertiary structure refers to three dimensional structure of a single protein molecule. The Alpha helix and the beta pleated sheets are folded into a compact globule. The folding is driven by the non specific hydrophobic interactions but the structure is stable only when the parts of a protein domain are locked into place by specific tertiary interactions such as salt bridges , hydrogen bonds and the tight packing of side chains and disulfide bonds.

Quaternary structure

It is the three dimensional structure of a multi-subunit protein. According to the number of sub-units, say 2 or 4, an oligomeric protein having identical subunits is called homo dimer or homo tetramer, while a protein with non identical subunits is called a hetero dimer or hetero tetramer.

Difference between alpha helix and beta pleated sheets
Bonds that stabilize the structure of protein:
  • Hydrogen bond: It stabilizes the secondary structure.
  • Electrostatic or ionic bond: It involved in tertiary and quaternary structures.
  • Hydrophobic interactions or bonds: The tertiary structure of a peptide chain is stabilized mainly by hydrophobic interactions between non polar amino acid side chains of the same peptide chain.
  • Vander Walls force: Helps to stabilize the Alpha helix secondary structure as well as tertiary and quaternary.
  • Disulfide bond: Stabilizes secondary, tertiary and quaternary structure.


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