Question

In a structural gene, the template DNA strand has nucleotide sequences: 3’ ATGCATGCATGCATGC 5’. Find the correct and complementary nucleotide sequence on the coding strand.

• A. 5’ ATGCATGCATGCATGC 3’
• B. 3’ GCATGCATGCATGCAT 5’
• C. 5’ TACGTACGTACGTACG 3’
• D. 3’ TACGTACGTACGTACG 5’

Hint:

DNA strands complement each other to maintain genetic fidelity.

Answer 1

The Correct Option is C

DNA strand complementarity:

Given template strand: 3'-ATGCATGCATGCATGC-5'

(A) 5'-ATGCATGCATGCATGC-3' - Incorrect: This is identical to the template strand, not complementary.

(B) 3'-GCATGCATGCATGCAT-5' - Incorrect: This is a shifted sequence with wrong polarity.

(C) 5'-TACGTACGTACGTACG-3' - Correct: This shows proper complementarity (A-T, G-C) and antiparallel orientation to the template strand.

(D) 3'-TACGTACGTACGTACG-5' - Incorrect: While the sequence is complementary, the polarity is wrong (should be 5'→3').

The correct answer is (C), demonstrating perfect Watson-Crick base pairing and proper 5'→3' orientation for the coding strand.

Answer 2

To find the complementary sequence on the coding strand:

1. The template strand is given as: 3′-ATG CAT GAT GCG ATG C-5′ .
2. The coding strand is complementary to the template strand and runs in the opposite direction (5′ to 3′).
3. To find the complementary sequence:
   • Replace each base with its complement: A ↔ T, T ↔ A, C ↔ G, G ↔ C.
   • Reverse the sequence to match the 5′ to 3′ orientation.

Starting with the template strand:
3′-ATG CAT GAT GCG ATG C-5′
Complement:
5′-TAC GTA CAT CGC TAC G-3′

Thus, the correct complementary sequence on the coding strand is:
5′-TAC GTA CAT CGC TAC G-3′

Final Answer:
(C) 5′-TAC GTA CAT CGC TAC G-3′