Question

5 cgctaa 3
which of the following nucleotide base sequences complements the section of dna modeled above?
a. 5 utcgca 3
b. 3 aatcgc 5
c. 5 ttucgc 3
d. 3 gcgatt 5

Explanation:

Step1: Recall DNA base - pairing rules

In DNA, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). Also, the complementary strand has an antiparallel orientation (if one strand is \(5'\to3'\), the complementary strand is \(3'\to5'\)).

Step2: Analyze each option

• Option A: DNA does not contain uracil (U). Uracil is found in RNA. So, this option is incorrect.
• Option B: Let's pair the bases. The given strand is \(5'\text{CGCTAA}3'\). If we consider the complementary strand \(3'\text{AATCGC}5'\), for the first base \(C\) (in \(5'\text{CGCTAA}3'\)), the complementary base should be \(G\) (not \(A\) as in \(3'\text{AATCGC}5'\)). So, this option is incorrect.
• Option C: DNA does not contain uracil (U). Uracil is found in RNA. So, this option is incorrect.
• Option D: For the strand \(5'\text{CGCTAA}3'\), the complementary bases (with antiparallel orientation) are:

\(C - G\), \(G - C\), \(C - G\), \(T - A\), \(A - T\), \(A - T\). The complementary strand is \(3'\text{GCGATT}5'\)

Answer:

D. \(3'\text{GCGATT}5'\)