Question

Types of coiling in DNA is

• A. Right handed
• B. Left handed
• C. Zig-zag
• D. Opposite

Answer 1

Answer: (A), (B)

The correct options are
A Right handed
B Left handed

DNA molecule is made up of two helical DNA chains that are wound around the same axis. DNA can occur in different dimensional structures which are namely B-DNA, A-DNA and Z-DNA. The A-DNA and B-DNA are arranged in a right-handed double helix, while Z-DNA is arranged in a left-handed double helix. To counteract the topological difficulties as faced during DNA unwinding, B DNA occur with alternating right and left handed segments in a repeat of 10bp. Thus, DNA occur in both right and left handed helix. Zigzag appearance of phosphate backbone is found in Z-DNA; it is not a type of coiling. Two successive nucleotides of DNA are joined by phosphodiester linkage. The same orientation of all phosphodiester linkages along the chain imparts each linear nucleic acid strand a specific polarity and distinct 5’ and 3’ ends. The two DNA strands are antiparallel and have opposite polarity means that 5’ end of one strand faces 3’ end of other strand and vice versa; it does not indicate coiling. Thus, the correct answers are A and B.