Question

Why are CpG sites considered palindromic in the context of DNA sequences?

A) They always have the sequence CGGC.
B) They exhibit the same string of nucleotides on both forward and reverse strands when read in the 5' → 3' direction.
C) They contain equal proportions of cytosine (C) and guanine (G).
D) They form a mirror image structure within the DNA helix.

Answer 1

CpG sites are palindromic because they read the same in the 5' → 3' direction on both strands of the DNA helix due to complementary base pairing.

Step-by-step explanation:

CpG sites are considered palindromic in the context of DNA sequences because they exhibit the same string of nucleotides on both forward and reverse strands when read in the 5’ → 3’ direction. This characteristic is due to the complementary base pairing inherent in DNA's double helix structure, where cytosine (C) pairs with guanine (G) across the two antiparallel strands. The correct choice is B, they exhibit the same string of nucleotides on both forward and reverse strands when read in the 5' → 3' direction. This complementarity allows for the sequences to be read the same way in both directions, much like a palindrome in language, which reads the same forwards and backwards.