Question 18

The DNA strand that complements ACTTGCA is TGAACGT.

The DNA strand that complements the segment ACTTGCA is TGAACGT, as it aligns perfectly with the base pairing rules of DNA.

A) TGAACGT

This option is correct because it is the complementary strand to ACTTGCA. According to the base pairing rules, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). Therefore, A complements T, C complements G, and the sequence reads TGAACGT when the original strand is ACTTGCA.

B) GACCATG

This option is incorrect because the sequence GACCATG does not match the required base pairing for the given strand. Specifically, the first base pair should be T (complementing A), but here it starts with G, which indicates a mismatch.

C) ACTTGCA

This option is incorrect as it simply repeats the original strand and does not provide a complementary sequence. Complementary strands consist of bases that pair with the original strand, and therefore ACTTGCA cannot complement itself.

D) None of the above

This option is incorrect because TGAACGT is indeed a valid complementary strand to ACTTGCA, thus negating the claim that none of the options fit.

Conclusion

The correct answer, TGAACGT, is definitively right as it follows the established base pairing rules for DNA. The other options either misrepresent the required complements or do not provide a valid pairing, demonstrating that only Option A fulfills the criteria set by the original DNA segment.