27. Which DNA strand would complement this segment: ACTTGCA?
Answer: A
The DNA strand that complements ACTTGCA is TGAACGT.
The complementary DNA strand for the segment ACTTGCA is TGAACGT, as adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G).
A) TGAACGT
This option correctly represents the complementary DNA sequence to ACTTGCA. Each base is matched appropriately: A pairs with T, C with G, T with A, G with C, and so on, resulting in the correct complement.
B) GACCATG
This option is incorrect as it does not match the expected pairing sequence. The bases do not align with the original strand ACTTGCA according to the base pairing rules of DNA.
C) ACTTGCA
This option is incorrect because it is the identical sequence rather than the complementary strand. Complementary strands must consist of paired bases, not the same sequence.
D) None of the above
This option is incorrect since there is a valid complementary strand provided. The existence of TGAACGT as a correct option means that "None of the above" does not apply.
Conclusion
The correct answer, TGAACGT, is definitively the complementary strand to ACTTGCA based on standard DNA base pairing rules. Options B, C, and D fail to provide a valid complementary sequence, reinforcing the correctness of option A.