Question

Which of these is a type of protein secondary structure?

• A. $\alpha$-helix
• B. $\beta$-pleated
• C. Collagen helix
• D. All the above

Answer 1

Answer: (D)

All the above

Alpha helix structure of the protein is one of the secondary structure forms of the protein. It is formed due to the formation of hydrogen bonds between backbone amide and carbonyl groups within a polypeptide chain. The hydrogen bonds are formed between N-H group of one amino residue with a C=O group of another amino acid which is placed in 4 residues earlier. Each turn of alpha helix contains 3.6 amino acid residues.

β-pleated secondary protein structure is formed by the parallel or anti-parallel polypeptide chains linked together by H- bonds. It is stabilized by the hydrogen bonds formed between NH and Co of the adjacent polypeptide chain. The distance between the adjacent amino acids is 3.5 A${}^o$.

Fibrous protein provides structural support to the cell. Alpha keratin and collagen are the two fibrous protein. Collagen has a singular secondary structure, helicoidal but more stretched or elongated than alpha helix and turning left instead of right-handed. So, the correct answer is option D.