Identify the correct options with respect to the salient features of DNA.
(A) The two polynucleotide chains are coiled in a left-handed fashion
(B) Adenine forms three hydrogen bonds with thymine
(C) The distance between a base pair in a DNA helix is approximately 0.34 nm
(D) The plane of one base pair stacks over the other in double helix
Choose the correct answer from the options given below :
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (C), (D)
(A) The two polynucleotide chains are coiled in a left-handed fashion — False. They are coiled in a right-handed fashion.
(B) Adenine forms three hydrogen bonds with thymine — False. Adenine forms two hydrogen bonds with thymine; G and C form three.
(C) The distance between a base pair in a DNA helix is approximately 0.34 nm — True.
(D) The plane of one base pair stacks over the other in double helix — True.
NCERT Extract:
Structure of Polynucleotide Chain – “… (iv) The two chains are coiled in a right-handed fashion. The pitch of the helix is 3.4 nm (a nanometre is one billionth of a metre, that is 10−9 m) and there are roughly 10 bp in each turn. Consequently, the distance between a bp in a helix is approximately 0.34 nm. (v) The plane of one base pair stacks over the other in double helix.”