Biology  by Bradford
IB Biology 2025 · Theme D · Continuity and change

D1.2 Protein synthesis. Practice questions with markscheme.

48 original IB-style questions on D1.2, written from the 2025 guide: 21 multiple-choice, 19 short-answer, 5 data-based, 2 extended-response part, 1 drawing. Below is a 20-mark standard-level practice paper built from them, ready to hand out as a class quiz or homework, or to sit yourself and mark against the scheme. Print it, project it, or build a fresh one on the same topic.

What the guide asks for

11 statements at SL and HL, 8 additional higher level.

  1. D1.2.1SL / HL Transcription as the synthesis of RNA using a DNA template
  2. D1.2.2SL / HL Role of hydrogen bonding and complementary base pairing in transcription
  3. D1.2.3SL / HL Stability of DNA templates
  4. D1.2.4SL / HL Transcription as a process required for the expression of genes
  5. D1.2.5SL / HL Translation as the synthesis of polypeptides from mRNA
  6. D1.2.6SL / HL Roles of mRNA, ribosomes and tRNA in translation
  7. D1.2.7SL / HL Complementary base pairing between tRNA and mRNA
  8. D1.2.8SL / HL Features of the genetic code
  9. D1.2.9SL / HL Using the genetic code expressed as a table of mRNA codons
  10. D1.2.10SL / HL Stepwise movement of the ribosome along mRNA and linkage of amino acids by peptide bonding to the growing polypeptide chain
  11. D1.2.11SL / HL Mutations that change protein structure
  12. D1.2.12HL Directionality of transcription and translation
  13. D1.2.13HL Initiation of transcription at the promoter
  14. D1.2.14HL Non-coding sequences in DNA do not code for polypeptides
  15. D1.2.15HL Post-transcriptional modification in eukaryotic cells
  16. D1.2.16HL Alternative splicing of exons to produce variants of a protein from a single gene
  17. D1.2.17HL Initiation of translation
  18. D1.2.18HL Modification of polypeptides into their functional state
  19. D1.2.19HL Recycling of amino acids by proteasomes

In the bank for D1.2

  • 21 multiple-choice
  • 19 short-answer
  • 5 data-based
  • 2 extended-response part
  • 1 drawing
  • 18 higher level only

Every question is original and tagged to a guide statement. See the whole bank →

Make your own

The practice paper

Take it on screen → Build a fresh paper Paper code BbB-EAAAAAAgABQAO8O_
Biology · topic quiz
Standard level · topic practice, not an exam format
30 minutes20 marks

Paper code: this paper was generated, so the code is its recipe. Enter it at biologybybradford.com/exam-maker to rebuild this exact paper and its markscheme.

Covers D1.2 Protein synthesis
Name:
1.

Explain how a single base substitution in a gene can change the structure and function of a protein, using sickle-cell haemoglobin as an example.

[3]
2.

The antibiotic chloramphenicol blocks the formation of peptide bonds by bacterial ribosomes. Predict, with reasons, its effect on protein synthesis in bacteria.

[3]
3.

Heat shock proteins help cells to survive high temperatures. Researchers grew cultures of baker's yeast (Saccharomyces cerevisiae) at 25 °C, then transferred samples to water baths at four temperatures for 30 minutes. In each sample they measured the relative amount of mRNA transcribed from the HSP70 gene and the rate of synthesis of the Hsp70 protein, using the incorporation of radioactively labelled methionine. In a second experiment, samples transferred to 37 °C were treated with actinomycin D, a chemical that binds to DNA and prevents RNA polymerase from moving along the template strand. The rate of synthesis of all proteins together (total protein) was also measured. Six cultures were tested for each treatment; values are means ± standard error (SE).

TreatmentRelative amount of HSP70 mRNA / arbitrary units (± SE)Rate of Hsp70 synthesis / counts min⁻¹ mg⁻¹ (± SE)Rate of total protein synthesis / counts min⁻¹ mg⁻¹ (± SE)
25 °C1.0 ± 0.2120 ± 152050 ± 140
30 °C1.4 ± 0.3160 ± 202150 ± 160
37 °C6.5 ± 0.6780 ± 602100 ± 150
42 °C7.1 ± 0.8850 ± 901650 ± 180
37 °C with actinomycin D0.8 ± 0.295 ± 121900 ± 170
(a)Describe the effect of temperature on the relative amount of HSP70 mRNA.[2]
(b)Calculate the percentage increase in the relative amount of HSP70 mRNA when the temperature was raised from 25 °C to 37 °C.[2]
(c)Deduce, with a reason, whether the difference in the amount of HSP70 mRNA between 37 °C and 42 °C is statistically significant.[2]
(d)Outline the relationship between the amount of HSP70 mRNA and the rate of synthesis of Hsp70 protein.[1]
(e)Explain the effect of actinomycin D on the rate of synthesis of Hsp70 at 37 °C.[2]
(f)Suggest why actinomycin D reduced the rate of total protein synthesis far less than the rate of Hsp70 synthesis.[2]
(g)The results show that transcription is a stage at which the expression of a gene can be switched on. Outline the role of RNA polymerase in transcription.[3]

Original practice questions © Biology by Bradford · CC BY-NC-SA 4.0 · Not affiliated with or endorsed by the International Baccalaureate Organization.
Rebuild or edit this exact paper (and its markscheme): biologybybradford.com/exam-maker?code=BbB-EAAAAAAgABQAO8O_

Show the markscheme

Markscheme BbB-EAAAAAAgABQAO8O_

One mark per point; / separates alternative wording within a point, OR separates alternative answers, words in brackets are not required, underlined words are essential. OWTTE = or words to that effect.

1. D1.2.11 [3 max]
  • the substitution changes one codon, so a different amino acid is placed in the polypeptide (glutamic acid → valine in the β-chain of haemoglobin);
  • the amino acid sequence (primary structure) determines how the polypeptide folds / its three-dimensional shape (R-group interactions);
  • (so) the protein's shape/(surface) properties change, altering its function;
  • (in sickle-cell anaemia) the mutant haemoglobin (HbS) is less soluble and polymerizes into fibres at low oxygen concentration, distorting red blood cells into sickle shapes (causing anaemia/blocked capillaries), OWTTE;
2. D1.2.10 [3]
  • amino acids can no longer be linked (by condensation) to the growing polypeptide chain;
  • (so) the chain cannot grow / no (complete, functional) polypeptides are made, even though mRNA and tRNAs can still bind to the ribosome;
  • (so) bacterial protein synthesis stops, halting growth of/killing the bacteria, OWTTE;
3. D1.2.1, D1.2.4
  • (a) [2 max]
    • little change / only a small increase between 25 °C and 30 °C (1.0 to 1.4);
    • a large increase between 30 °C and 37 °C (1.4 to 6.5 / more than four-fold);
    • only a small further increase from 37 °C to 42 °C (6.5 to 7.1) / the amount levels off;
    • overall, the amount of HSP70 mRNA increases with temperature, OWTTE;

    At least one figure from the table is required for [2].

  • (b) [2]
    • (6.5 − 1.0) ÷ 1.0 × 100;
    • 550 %;

    Award [2] for 550 % with or without working. Accept 545–555 %. Award [1] for 650 % (the value at 37 °C as a percentage of the value at 25 °C, rather than the increase) or for correct working with an arithmetic slip.

  • (c) [2 max]
    • not significant / the difference cannot be shown to be significant;
    • the ranges given by the standard errors overlap / 6.5 ± 0.6 extends up to 7.1 and 7.1 ± 0.8 extends down to 6.3;
    • (so) the difference could be due to chance / sampling variation, OWTTE;

    Do not award the first point without a reason based on the standard errors.

  • (d) [1 max]
    • positive correlation / the more HSP70 mRNA present, the faster Hsp70 is synthesized;
    • the rate of synthesis is (approximately) directly proportional to the amount of mRNA / about 120 counts min⁻¹ mg⁻¹ per unit of mRNA at every temperature;
  • (e) [2 max]
    • actinomycin D prevents transcription of the HSP70 gene, because RNA polymerase cannot move along the template strand;
    • (so) little or no new HSP70 mRNA is produced / mRNA stays at the low level present before the heat shock (0.8 compared with 6.5);
    • (so) there is very little mRNA for ribosomes to translate, and Hsp70 synthesis falls (from 780 to 95 / by about 88 %);
  • (f) [2 max]
    • mRNA for most other proteins was already present in the cells / was transcribed before actinomycin D was added;
    • actinomycin D does not affect translation (ribosomes, tRNA), so these existing mRNA molecules continue to be translated;
    • mRNA persists for some time before it is broken down, so protein synthesis continues during the 30 minutes;
    • (whereas) HSP70 mRNA was scarce before the heat shock, so Hsp70 could only be made if the gene was newly transcribed, OWTTE;
  • (g) [3 max]
    • RNA polymerase binds to (the promoter / start of) the gene on the DNA;
    • it unwinds / separates the two DNA strands (breaking hydrogen bonds) to expose the template strand;
    • it moves along the template strand, adding free RNA nucleotides that pair with the template bases by complementary base pairing (A with U, T with A, C with G, G with C);
    • it forms (covalent / phosphodiester) bonds between adjacent RNA nucleotides, building the RNA strand in the 5′ to 3′ direction;
    • it releases the RNA transcript (and detaches from the DNA) at the end of the gene, and the DNA double helix re-forms;

    Content pivot. Accept any three.

More in Theme D · Continuity and change

All 40 IB Biology subtopics →  ·  AP Biology units →  ·  Open the exam maker →