Question

each strand of a dna molecule contains nitrogenous bases that pair with other nitrogenous bases in very specific ways. a diagram of a section of dna is shown.
which dna strand is complementary to the one shown above?

Explanation:

Step1: Recall DNA base - pairing rules

In DNA, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). Also, the strands are anti - parallel. If one strand is \(5'\to3'\), the complementary strand is \(3'\to5'\).
The given strand is \(5' - TGTAGCTGCCGCGT - 3'\).

Step2: Find the complementary bases

For each base in the given strand:

• \(T\) (in \(5'\) - strand) pairs with \(A\)
• \(G\) pairs with \(C\)
• \(T\) pairs with \(A\)
• \(A\) pairs with \(T\)
• \(G\) pairs with \(C\)
• \(C\) pairs with \(G\)
• \(T\) pairs with \(A\)
• \(G\) pairs with \(C\)
• \(C\) pairs with \(G\)
• \(G\) pairs with \(C\)
• \(C\) pairs with \(G\)
• \(G\) pairs with \(C\)
• \(T\) pairs with \(A\)

The complementary strand (in \(3'\to5'\) direction) is \(ACATCGACGCGCA\). When written in \(5'\to3'\) direction (since DNA strands are usually represented in \(5'\to3'\) direction in such questions, and we reverse the order of the \(3'\to5'\) complementary sequence), we get \(5' - ACATCGACGCGCA - 3'\) which is equivalent to option \(H\) (\(5' - ACATCGACGCGCA - 3'\)) after re - checking base - pairing.

Answer:

H. \(5' - ACATCGACGCGCA - 3'\)