Genetic code: wobble hypothesis: 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 · Genetic code: wobble hypothesis

Sample item

A tRNA for alanine has inosine in the first position of its anticodon. According to the wobble hypothesis, which alanine codons can this single tRNA read?

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

The answer and the reasoning

C. GCU, GCC and GCA

The first anticodon base pairs with the third codon base, where pairing is relaxed. Inosine can pair with U, C and A, so one tRNA reads three of the four alanine codons. G at the same position reads U and C, and U reads A and G. A different tRNA is needed for GCG.

Option by option

  • A. GCU, GCC, GCA and GCG

    Inosine does not pair efficiently with G, so GCG needs another tRNA.

  • B. GCU only

    This underestimates wobble; inosine is not specific for U only.

  • C. GCU, GCC and GCA (correct)

    Correct. Inosine pairs with U, C and A at the wobble position.

  • D. GCC and GCG only

    Inosine does not pair preferentially with C and G only.

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 C, GCU, GCC and GCA. The first anticodon base pairs with the third codon base, where pairing is relaxed.

Why is "GCU, GCC, GCA and GCG" not the answer?

Inosine does not pair efficiently with G, so GCG needs another tRNA.

Why is "GCU only" not the answer?

This underestimates wobble; inosine is not specific for U only.

Why is "GCC and GCG only" not the answer?

Inosine does not pair preferentially with C and G only.

What concept does this question test?

It tests Genetic code: wobble hypothesis in Biochemistry. Inosine can pair with U, C and A, so one tRNA reads three of the four alanine codons. G at the same position reads U and C, and U reads A and G. A different tRNA is needed for GCG.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Genetic code: wobble hypothesis?

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.