In a DNA double helix, what is the sequence of the complementary strand (written 5′→3′) to the strand 5′-AGTC-3′?

• A. 5′-GACT-3′
• B. 5′-TCAG-3′
• C. 5′-CAGT-3′
• D. 5′-AGTC-3′

Answer: (A)

Verified step by step guidance

1. Identify the given DNA strand sequence and note its direction: 5′-AGTC-3′.
2. Recall that DNA strands are antiparallel, meaning the complementary strand runs in the opposite direction (3′ to 5′) relative to the original strand.
3. Determine the complementary bases using base pairing rules: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C).
4. Write the complementary bases in the 3′ to 5′ direction opposite to the original strand, which will be 3′-TCAG-5′.
5. Reverse the complementary strand to write it in the 5′ to 3′ direction, resulting in 5′-GACT-3′.