Refer to the given figure.
Formation of structures A and B could be due to

Answer: BSolution: The folding of a linear polypeptide chain into a specific coiled structure is referred to as the secondary structure of the protein. Such coiling or folding is produced by hydrogen bonds. The importance of such folding lies in the fact that amino acid residues which may lie far apart in their primary sequence are brought together in close proximity by secondary folding. There are three types of secondary structures $-\alpha$-helic $\beta -$ pleated sheets and collagen helix.
In $\alpha$-helix, hydrogen bonds between oxygen of carboxylic group of one amino acid residue and NH group of next amino acid residue In $\beta$-plated secondary structure, two or more polypeptide chains get interconnected by hydrogen bonds. Adjacent strands pf polypeptides may rum in the same direction (parallel $\beta$-sheet, e.g., $\beta$-keratin) or in opposite directions (antiparallel $\beta$-sheet, e.g., ibroin of silk).