Question

If one strand of a DNA molecule has the sequence of bases 5' ATTGCA 3', the other complementary strand would have the sequence (pay attention to the direction of the strands):

1) 5' UAACGU 3'
2) 5' TGCAAT 3'
3) 3' UAACGU 5'
4) 5' TAACGT 3'

Answer 1

The complementary strand to 5' ATTGCA 3' would be the sequence that follows base pairing rules and is antiparallel to the given sequence, meaning the correct direction is from 3' to 5'.

Step-by-step explanation:

If one strand of a DNA molecule has the sequence of bases 5' ATTGCA 3', the sequence of the complementary strand going in the opposite direction, that is, the antiparallel direction, would be identified following the base pairing rules where adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G). So for the given sequence, the complementary strand would read 3' TAACGT 5', which reflects the antiparallel nature of DNA and correct base pairing.

This means that option 4, which presents the sequence 5' TAACGT 3', is incorrect because it does not consider the reverse direction of the complementary strand (it should be 3' to 5', not 5' to 3'). Instead, the correct complements would be A with T, T with A, T with A, G with C, C with G, and A with T, considering the antiparallel orientation.