Question

.What will be length of α-heical section of a polypeptide chain containing 15 amino acids ?​

Answer 1

A 20-amino-acid motif called a helix–turn–helix domain has been identified in several different DNA binding proteins. The structure of this protein domain is an 8-amino-acid α helix followed by a right “turn” consisting of 3 amino acids followed by another α helix of 9 amino acids. There are three positions in the helix–turn–highly conserved helix motif. An alanine is usually found at position 5 within the first α helix; a glycine is found at position 9, the first position of the turn; and either valine or isoleucine is usually found at position 15 within the second α helix. These critical positions are believed to be responsible for maintaining the structure of helix–turn–helix rather than specifying contacts with the DNA. Except for those conserved positions, there is a great deal of heterogeneity in the amino acid composition of other positions within this protein motif.