IB Biology SL D1.2 Protein synthesis questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

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Question 1

Multiple choiceEasy1 mark

A particular gene is inactive in a non-dividing somatic cell. Which description is consistent with the gene having been switched off at the first stage of gene expression?

Show answer and explanation

Answer: A. The first stage of gene expression is transcription. When transcription is switched off, no new RNA is transcribed from the gene; using DNA as a template does not change its base sequence.

B: assumes that switching off transcription alters the DNA sequence.
C: confuses switching off transcription with continued transcription while a later stage is inactive.
D: assumes the DNA template is consumed or destroyed rather than used without changing its sequence.

Remember: transcription changes gene expression, not the DNA base sequence.

Question 2

Paper 2Medium4 marks

Figure 1 shows a stage in the elongation of a polypeptide during protein synthesis.

ribosome5′3′AUGGCUUUUCAAgrowing polypeptide chain3′-CGA-5′
(a)

State the next mRNA codon to be translated as elongation continues.

[1]
(b)

Explain how the ribosome adds the next amino acid and continues elongation from the stage shown in Figure 1.

[3]

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