α-helix
- 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.