Question

1) Which amino acid side chains that can act as an H-donor and acceptor at all pH values (0-14)?

2)Which amino acid is commonly found in a beta or reverse turn?

3) Which amino acid side chain could NOT form an ionic or electrostatic interaction at any pH value (0-14)?

Options: Cysteine, Isoleucine, Aspartate, Glutamine, Methionine

Pls explain why, thanks.

Answer 1

ans 1 .

• 3 amino acids (arginine, lysine and tryptophan) have hydrogen donor atoms in their side chains.
• 2 amino acids (aspartic acid, glutamic acid) have hydrogen acceptor atoms in their side chain.
• 6 amino acids (asparagine, glutamine, histidine, serine, threonine and tyrosine) have both hydrogen donor and acceptor atoms in their side chains.

ans 2

Proline and Glycine are frequently found in beta turns, proline because its cyclic structure is ideally suited for the beta turn, and glycine because, with the smallest side chain of all the amino acids, it is the most sterically flexible

ans 3. cysteine, isolucene ,methionine

These 9 amino acids (alanine, cysteine, glycine, isoleucine, leucine, methionine, phenylalanine, proline, valine) have no hydrogen donor or acceptor atoms in their side chains.Therefore , they cannot form ionic or electrostatic interactions.