In a palindromic DNA sequence:
AThe sequence reads the same forward and backward on the same strand
BOnly A and T bases occur
CThe sequence has no specific pattern
DThe sequence reads the same in the 5′→3′ direction on both complementary strands (e.g., 5′-GAATTC-3′ on top strand has 5′-GAATTC-3′ on bottom strand)
Answer & Solution
Correct answer: D. The sequence reads the same in the 5′→3′ direction on both complementary strands (e.g., 5′-GAATTC-3′ on top strand has 5′-GAATTC-3′ on bottom strand)
**DNA palindrome** = sequence reads the **same 5′→3′ on both strands** (not 'same forward and backward' on one strand, like a word palindrome). Necessary for restriction-enzyme recognition because the enzyme is a homodimer with two-fold rotational symmetry.
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