<prompt> Which amino acid induces bends in a helix?GlycineValineLeucineIsoleucine  <response>: Ans. is a i.e., Glycine Two amino acids are involved in producing folds in collagen : proline and glycine. In order to form a triple-helix a polypeptide chain a-chain must contain glycine as every third residue in the sequence. This is because only the glycine is small enough to be accommodated in the limited space available down the central core of the triple helix. Each turn of polypeptide chain a-chain contains three amino acid residues, and glycine Gly is present at every third position. Thus glycine constitutes 33 of the total amino acid residues. The repeating amino acid residues, represented as Gly-X-Yn, is an absolute requirement for formation of triple helix. X and Y can be any amino acids, but most of the time X is proline 10 of the total amino acid residues and most of the time Y is hydroxyproline. Other important amino acids found in collagen are lysine and hydroxylysine. Two amino acids helps in formation of triple-helixi. Proline: Introduces sharp bends in the polypeptide chains a-chainsii Glycine: It plays an indirect role in permitting extremely tight interwinding of the a-chains. The winding is so compact that there is little space available towards the interior, only the smallest amino acid i.e. glycine can be accomodated at this place. 