a-helix of protein is ?

Ans. is 'b' i.e., Secondary structure a-helix It is a spiral structure consisting of a polypeptide chain that is coiled around a longitudinal axis in a helical fashion.It is the most common secondary structure and a vast variety of proteins contain the a-helical structure.The a-helix is produced by formation of hydrogen bonds between peptide linkages three amino acid residue apa. That means hydrogen bonds are formed between the first and the fouh peptide linkages, between the second and fifth peptide linkage and so on.Each peptide linkage in the polypeptide chain paicipates in hydrogen bonding and hydrogen bonds are formed between peptide linkages of same peptide chain.There are 3.6 amino acids residues in each turn of the helix.The pitch (veical distance per turn) of the helix is 5.4 Adeg.Each hydrogen bond has nitrogen to oxygen distance (N-0) 2.8Adeg.All hydrogen bonds are paralled, i.e., in the same direction.The helix may be right-handed (coils turn in a clockwise fashion around the axis) or left handed (coils turn in anti-clock wise fashion).Right-handed helix are more stable.Right handed a-helix is the commonest secondary structure found in proteins.