Haemoglobin: structure and mutations: 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.

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Biochemistry · Haemoglobin: structure and mutations

Sample item

In sickle cell disease the substitution of valine for glutamate at position 6 of the beta chain promotes polymerisation of deoxyhaemoglobin. What type of mutation is this?

ASplice-site mutationBNonsense mutationCMissense point mutationDFrameshift deletion

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

The answer and the reasoning

C. Missense point mutation

A single nucleotide change (GAG to GTG) replaces glutamate with valine, which is a missense mutation. The hydrophobic valine forms a sticky patch that binds the beta chain of another haemoglobin molecule in the deoxy state.

Option by option

A. Splice-site mutation
Splice-site mutations alter RNA processing, as in some beta thalassaemias.
B. Nonsense mutation
A nonsense mutation creates a stop codon, as in some beta thalassaemias.
C. Missense point mutation (correct)
Correct. One codon is changed to code for a different amino acid.
D. Frameshift deletion
Frameshift mutations alter the reading frame through insertions or deletions.

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.

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Missense point mutation. A single nucleotide change (GAG to GTG) replaces glutamate with valine, which is a missense mutation.

Why is "Splice-site mutation" not the answer?

Splice-site mutations alter RNA processing, as in some beta thalassaemias.

Why is "Nonsense mutation" not the answer?

A nonsense mutation creates a stop codon, as in some beta thalassaemias.

Why is "Frameshift deletion" not the answer?

Frameshift mutations alter the reading frame through insertions or deletions.

What concept does this question test?

It tests Haemoglobin: structure and mutations in Biochemistry. The hydrophobic valine forms a sticky patch that binds the beta chain of another haemoglobin molecule in the deoxy state.

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 Haemoglobin: structure and mutations?

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.