Question

1. the base sequence of a segment of dna is shown.

dna strand 1: 3 g c g t a c 5
dna strand 2: 5 ? ? ? ? ? ? 3
which base sequence correctly completes dna strand 2?

Explanation:

Step1: Recall base - pairing rules

In DNA, \(G\) (guanine) pairs with \(C\) (cytosine) and \(A\) (adenine) pairs with \(T\) (thymine). Also, the strands are anti - parallel. DNA Strand 1 is \(3'\text{GCGTAC}5'\).

Step2: Determine complementary bases

For the first base \(G\) in Strand 1 (\(3'\) end), the complementary base is \(C\). For the second \(C\), it is \(G\). For the third \(G\), it is \(C\). For the fourth \(T\), it is \(A\). For the fifth \(A\), it is \(T\). For the sixth \(C\), it is \(G\). And since Strand 1 is \(3'\to5'\), Strand 2 is \(5'\to3'\). So the sequence of Strand 2 is \(5'\text{CGCATG}3'\).

Answer:

C. \(CGCATG\)