If one strand of a DNA molecule contains 22% adenine, what percentage of the whole molecule is guanine?
Correct answer: B. 28%
- A. 22%
- B. 28%
- C. 44%
- D. 56%
Explanation
Chargaff's rule applies to the double stranded molecule, so A equals T and G equals C. With A at 22%, T is also 22%, leaving 100 minus 44 which is 56% shared equally between G and C, giving 28% guanine. The common error is to stop at 56% and forget that it is split between two bases.
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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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