Leucine amino acid is:

What is the number of amino acids present in a single turn of an $\alpha$-helix of a protein?

Which of the following is not an amino acid?

The secondary structure of proteins is stabilized by which bond?

Which of the following molecules has the ability to form a zwitterion?

Among the $\alpha$-amino acids - threonine,tyrosine,methionine,arginine and tryptophan,those which contain an aromatic group in their side chain are