Protein Biochemistry | BSc & MSc . – 2


  • Pauling and Corey in 1951 identified that polypeptide chain with planar peptide bond would form a right handed helical structure
  • by twisting about α carbon to nitrogen (C-N) or    α-carbon to the carboxyl carbon (C-C) bond.
  • Such helical form is called α helix.
  • Contains H – Bonding (Intra molecular ).
  • Helix can be right handed or left handed.
  • Is stable conformation of secondary structure of protein with lowest amount of energy.
  • The small and unchanged amino acids like (alanine, leucine and phenyl alanine )are present in α-helix .
  • Proline is not found in α-helix
  • The protein of hair, nail, skin contains keratin which is very rich in α-helix structure.

 β-pleated sheet

  • Pauling and Corey in 1953 identified second type of structure of protein having minimum energy and stable conformation called β-pleated sheet.
  • The name given was second because it was second structure and for first they named α structure.
  • There occurs intermolecular H – bonding.
  • The pleated sheet structure is formed by parallel alignment of number of polypeptide chain in a plane forming hydrogen bond between C – H and NH group of adjacent chain.
  • The structure is pleated due to the angles of bonds.

The tertiary structure of the protein

  • Protein tertiary structure is the three dimensional shape of a protein.
  •  The tertiary structure will have a single polypeptide chain “backbone” with one or more protein secondary structures, the protein domains.
  • Amino acid side chains may interact and bond in a number of ways.
  • Tertiary structure of protein is resulted by steric relationship between amino acids located very far but brought close by folding.
  • The tertiary structure of protein are mainly found in globular protein.
  • X – ray crystallographic studies identified tertiary structure of protein.

Quaternary structure

  • Protein – protein interaction or multi chain association.
  • The quaternary structure refers to the number and arrangement of the protein subunits with respect to one another.
  •  Examples of proteins with quaternary structure include hemoglobin, DNA polymerase, and ion channels.

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