Which of the following pairs of base sequences could form a short stretch of a normal double helix of DNA? a. 5′-AGCT-3′ with 5′-TCGA-3′ b. 5′-GCGC-3′ with 5′-TATA-3′ c. 5′-ATGC-3′ with 5′-GCAT-3′ d. All of these pairs are correct.

Video transcript

So here we have a problem that gives us a short D. N. A sequence and asks us to identify its complementary strand. So this is a pretty straightforward problem. First, we want to think about the fact that the complementary strand will bind in an anti parallel direction, so it will go in the direction three prime to five prime. And knowing that allows us to eliminate right away two of the choices over here, A and B. Since they are not in the correct direction, then we'll go ahead and look at the base pairs, knowing that C will be complementary to G. And then these two A's complementary to D. We don't even have to finish the strand. We can look over here and check and right away. We see that we can eliminate D. Since it doesn't have the correct bases. And therefore by elimination, we know the correct answer is C.