In a double helix, the base pairing rules are:

Question

BlackTom AI · Accepted Answer

Watson-Crick base pairing pairs adenine (A) with thymine (T) and guanine (G) with cytosine (C).

Relevant knowledge points: DNA is a double helix of two antiparallel strands held together by specific hydrogen bonds between nucleotide bases. Purines (A and G) are two-ring structures; pyrimidines (C and T) are single-ring. Chargaff’s rules state that in double-stranded DNA the amount of A equals T and the amount of G equals C.

Step-by-step reasoning:
1. Chemical complementarity: Adenine has hydrogen bond donor/acceptor groups positioned to form two hydrogen bonds with thymine; guanine and cytosine align to form three hydrogen bonds. These specific donor–acceptor geometries make A–T and G–C the only stable Watson-Crick pairs.
2. Structural constraint: Pairing a purine with a pyrimidine preserves the uniform width of the helix (~20 Å). A purine–purine pair (A–G) would be too wide; a pyrimidine–pyrimidine pair (C–T, etc.) would be too narrow, disrupting helix geometry.
3. Empirical evidence: Chargaff’s measured base composition shows equal A and T, equal G and C, confirming these pairings in double-stranded DNA.
4. Example: If one strand reads 5′-ATGC-3′, the complementary strand is 3′-TACG-5′, demonstrating A↔T and G↔C.

Why the correct answer is correct: A–T and G–C pairing satisfies hydrogen-bonding patterns, preserves helix dimensions, and matches experimental base ratios; G–C triple bonding also explains their higher thermal stability compared to A–T pairs.

Why other options are incorrect:
- "A to G, and T to C.": A–G is purine–purine (too wide) and hydrogen-bond geometry does not support stable Watson-Crick pairing.
- "A to A, G to G, T to T, and C to C": self-pairing would be chemically unfavorable and break helix uniformity.
- "A to C, and T to G.": These are mismatches with incompatible hydrogen-bond donors/acceptors (except occasional wobble in RNA), not canonical DNA base pairs.

Final confirmation: The correct base-pairing rule is "A to T, and G to C," which matches the provided answer.

In a double helix, the base pairing rules are:单项选择题

类似问题

From the DNA sequence 5' ATGGCGT 3', what is expected to be its complementary DNA sequence?

What is the complementary DNA strand of 3’….ATGGCTTGA….5’?

What single stranded DNA complements the sequence 5’TAG-ATG-TGG3’?

When forming hydrogen bonds, guanine will bond with?

What is the sequence of the complementary DNA strand of the sequence shown below. 5’….CCAGATTTCAGCG….3'?

The complementarity of DNA strand is based on

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单