Nucleic acid structure: Chargaff rules: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

Try it

Biochemistry · Nucleic acid structure: Chargaff rules

Sample item

In a sample of double-stranded DNA, adenine makes up 22% of the bases. What is the percentage of guanine?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. 28%

Chargaff rules state that A = T and G = C in double-stranded DNA. If A is 22%, T is also 22%, so A + T is 44% and G + C is 56%. Guanine is half of that, which is 28%.

Option by option

  • A. 28% (correct)

    Correct. G = (100 - 44) / 2 = 28%.

  • B. 44%

    44% is the combined A + T.

  • C. 22%

    22% is the percentage of thymine, which equals adenine.

  • D. 56%

    56% is the combined G + C, not guanine alone.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is A, 28%. Chargaff rules state that A = T and G = C in double-stranded DNA.

Why is "44%" not the answer?

44% is the combined A + T.

Why is "22%" not the answer?

22% is the percentage of thymine, which equals adenine.

Why is "56%" not the answer?

56% is the combined G + C, not guanine alone.

What concept does this question test?

It tests Nucleic acid structure: Chargaff rules in Biochemistry. If A is 22%, T is also 22%, so A + T is 44% and G + C is 56%. Guanine is half of that, which is 28%.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Nucleic acid structure: Chargaff rules?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.