Question

1. a dna sequence is shown.

5atcggctag3
which strand represents the complementary dna sequence?
5tacggatc3
5atcggctag3
3tagcgatc5
3gatcggcta5
clear all

Explanation:

In DNA, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). Also, the complementary strand runs in the opposite direction (antiparallel). The original strand is \(5'\text{ATCGGCTAG}3'\).

• For each base: A→T, T→A, C→G, G→C.
• The direction of the complementary strand will be \(3'\) to \(5'\).

Let's check each option:

• Option \(5'\text{TACGGATC}3'\): Incorrect direction (should be \(3'\) to \(5'\)) and incorrect base - pairing in some positions.
• Option \(5'\text{ATCGGCTAG}3'\): This is the same as the original strand, not complementary.
• Option \(3'\text{TAGCGATC}5'\): Incorrect base - pairing (e.g., in the original strand, the first base is A, which should pair with T, but here the first base is T which would pair with A if it were in the correct orientation, but also the length and some middle base - pairings are wrong).
• Option \(3'\text{GATCGGCTA}5'\):
• \(5'\text{A}\) in the original strand pairs with \(3'\text{T}\) in the complementary strand.
• \(5'\text{T}\) pairs with \(3'\text{A}\).
• \(5'\text{C}\) pairs with \(3'\text{G}\).
• \(5'\text{G}\) pairs with \(3'\text{C}\).
• \(5'\text{G}\) pairs with \(3'\text{C}\).
• \(5'\text{C}\) pairs with \(3'\text{G}\).
• \(5'\text{T}\) pairs with \(3'\text{A}\).
• \(5'\text{A}\) pairs with \(3'\text{T}\).
• \(5'\text{G}\) pairs with \(3'\text{C}\). And it has the correct \(3'\) to \(5'\) direction.

Answer:

\(3'\text{GATCGGCTA}5'\) (assuming this is the correct - paired and oriented option among the given choices based on base - pairing rules (A - T, C - G) and antiparallel orientation)