Question

In $\beta$-pleated secondary structure

• A. Polypeptides show alternate reverse helix
• B. Two or more polypeptides form sheet and run parallel
• C. Two or more polypeptides form sheet but the polypeptides run anti-parallel
• D. Both B and C

Answer 1

Answer: (D)

Both B and C

A few types of secondary structures are particularly stable and occur widely in proteins. The term secondary structure refers to the local conformation of some part of the polypeptide. The most prominent secondary structures are the alpha helix and the beta conformations. The beta conformation is a more extended conformation of polypeptide chains as compared to the alpha helix. In the beta conformation, the backbone of the polypeptide chain is extended into a zigzag rather than a helical structure which is seen in alpha helix. The zigzag polypeptide chains are arranged side by side form a structure identical to a series of pleats, hence the name beta (pleated) confirmation or beta sheet. In this, the hydrogen bonds are formed between adjacent segments of polypeptide chains. The adjacent polypeptide chains in a beta sheet can either be parallel (having the same amino-to-carboxyl orientation) or antiparallel (having opposite amino-to-carboxyl orientation). Hence the correct answer is option D.