In a double stranded DNA molecule, adenine pairs with thymine through
Correct answer: B. two hydrogen bonds
- A. one hydrogen bond
- B. two hydrogen bonds
- C. three hydrogen bonds
- D. a covalent bond
Explanation
Adenine and thymine are held together by two hydrogen bonds, while guanine and cytosine are held by three. That difference is why a DNA region rich in G and C needs a higher temperature to separate the strands, a fact used directly when designing PCR conditions. The covalent bonds in DNA run along each backbone, not across the strands.
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About Structure of DNA
DNA structure includes nucleotides made of deoxyribose, phosphate and nitrogenous bases, arranged in two antiparallel polynucleotide strands. Questions cover the double helix, phosphodiester and hydrogen bonds, complementary base pairing between adenine and thymine and between guanine and cytosine, and the significance of major and minor grooves.
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