Base Pairing Rules During DNA Synthesis When DNA polymerase encounters guanine (G) on the template (parental) strand, which nucleotide does it add to the growing daughter strand?

Introduction / Context:High-fidelity DNA replication relies on specific base pairing (Watson–Crick rules). Knowing which nucleotide is incorporated opposite each template base is fundamental to molecular genetics and PCR design.

Given Data / Assumptions:

• Template base is guanine (G).
• DNA polymerase synthesizes 5′→3′ by complementarity.
• Nucleotides are deoxyribonucleotides (no uracil in DNA).

Concept / Approach:According to base-pairing rules, G pairs with C via three hydrogen bonds in B-form DNA. Therefore, the correct incoming deoxyribonucleotide is dCTP, which becomes cytosine (C) in the daughter strand after incorporation and pyrophosphate release.

Step-by-Step Solution:

Verification / Alternative check:Melting temperature correlations show G≡C pairs (three H-bonds) contribute greater stability than A=T pairs (two H-bonds), aligning with the rule used here.

Why Other Options Are Wrong:

• Phosphate is not a nucleotide base.
• Uracil is in RNA, not DNA.
• Guanine opposite G would be mismatched.
• Adenine pairs with thymine, not guanine.

Common Pitfalls:Confusing RNA and DNA bases; forgetting that polymerase requires triphosphate forms (dNTPs) but incorporates the base + sugar + one phosphate into DNA.

Final Answer:Cytosine