IB Biology SL D1.2 Protein synthesis Questions

Practise IB Biology SL D1.2 by tracing DNA to mRNA and codons to amino-acid sequences at the ribosome, using strand orientation and the genetic code.

46 questions in this syllabus scope, with question parts counted together.

Syllabus
First assessment 2025
Course
Biology SL
Level
SL

Exam analysis

SL · 2010–2025
Papers with this topic42 / 141in the analysed sample
Latest appearanceNovember 2025
Tagged question parts52
Paper types5

Most tested objectives

  1. D1.2.8—Genetic code features9 papers
  2. D1.2.5—Translation7 papers
  3. D1.2.6—Roles in translation6 papers
  4. D1.2.11—Mutations changing protein structure6 papers
  5. D1.2.1—Transcription5 papers

Common question formats

  • Process explanation
  • Definition or recall
  • Calculation
  • Diagram interpretation
  • Data analysis
  • Comparison
  • Structured response

Recent exam appearances

November 2025Paper 2 SL · TZ1Q2(b), 2(c)[ 4 ]
November 2025Paper 1A SL · TZ1Q6[ 1 ]
May 2025Paper 2 SL · TZ3Q7(b)[ 4 ]

141 papers analysed · Tagging incomplete

Exam points

  • explain RNA polymerase transcription from a DNA template to complementary mRNA
  • derive mRNA from a DNA template using A–U/C–G pairing and check strand orientation
  • explain translation as ribosomes decoding mRNA codons into a growing polypeptide through tRNA and peptide bonds
  • identify mRNA, tRNA and ribosome roles, including anticodon pairing and tRNA charging
  • explain the triplet, degenerate and near-universal genetic code, including start and stop signals
  • convert template DNA to mRNA, then use a genetic-code table to derive the amino-acid sequence
  • trace a beta-haemoglobin base substitution to Glu→Val, altered protein structure and sickle-cell effects

Covered syllabus points

D1.2.1—TranscriptionD1.2.2—Hydrogen bonding in transcriptionD1.2.3—DNA template stabilityD1.2.4—Transcription for gene expressionD1.2.5—TranslationD1.2.6—Roles in translationD1.2.7—Complementary base pairingD1.2.8—Genetic code featuresD1.2.9—Using genetic code tableD1.2.10—Elongation of polypeptideD1.2.11—Mutations changing protein structure

Exam points

  • State that transcription produces mRNA as a mobile copy of gene information.
  • Describe how RNA polymerase makes an RNA strand complementary to the DNA template.

Question 1

[Maximum number: 1]

The antibiotic rifampicin is widely used to treat bacterial infections. It kills bacterial cells by interfering with transcription during protein synthesis. Which process would be directly prevented by rifampicin?

A

Base pairing between mRNA codons and tRNA anticodons

B

Bonding between amino acids

C

Movement of tRNA to the ribosome

D

Synthesis of mRNA from DNA

Exam points

  • Apply complementary base pairing during transcription, matching DNA adenine with RNA uracil and cytosine with guanine.

Question 1

[Maximum number: 1]

This is a sequence of nucleotides from a section of mRNA.
AUGAAACGCACGCAG
From which DNA sequence has it been transcribed?

A

ATGAAACGCACGCAG

B

UACUUUGCGUGCGAC

C

TACUUUGCGTGCGTC

D

TACTTTGCGTGCGTC

No public sample questions are available for this syllabus point yet.

Exam points

  • Identify which gene shows the greatest mRNA expression at a given time or under a given condition.
  • Compare mRNA expression across genes or varieties over time to describe how transcription changes with the condition.

Question 1

[Maximum number: 7]

Rice (Oryza sativa) is usually intolerant to sustained submergence under water, although it grows rapidly in height for a few days before dying. This is true for one variety, Oryza sativa japonica. The variety Oryza sativa indica is much more tolerant to submergence.

Three genetically modified forms of O. sativa japonica, GMFA, GMFB and GMFC, were made using different fragments of DNA taken from O. sativa indica.

The plants were then submerged for a period of 11 days. The heights of all the plants were measured at the beginning and at the end of the submergence period.

Figure for Question 1 — IB Biology SL
Figure for Question 1 — IB Biology SL

Question (a)

(a)

In the same experiment, the researchers hypothesized that the capacity to survive when submerged is related to the presence of three genes very close to each other on rice chromosome number 9; these genes were named Sub1A, Sub1B and Sub1C. The photograph below of part of a gel shows relative amounts of messenger RNA produced from these three genes by the submergence-intolerant variety, O. sativa japonica, and by the submergence-tolerant variety, O. sativa indica, at different times of a submergence period, followed by a recovery period out of water.

Figure for Question (a) — IB Biology SL
[ 5 ]

Question (i)

(i)

Determine which gene produced the most mRNA on the first day of the submergence period for variety O. sativa japonica.

[ 1 ]

Question (ii)

(ii)

Outline the difference in mRNA production for the three genes during the submergence period for variety O. sativa indica.

[ 2 ]

Question (iii)

(iii)

Compare the mRNA production for the three genes during the submergence period between the two varieties.

[ 2 ]

Question (b)

(b)

Deduce, using all the data, which gene was used to modify GMFC.

[ 2 ]

Exam points

  • Explain how ribosomes decode mRNA codons to synthesize a polypeptide.
  • Relate each mRNA codon to an amino acid to explain how codon order sets polypeptide sequence.

Question 1

[Maximum number: 1]

What occurs during translation?

I. Polypeptides synthesised on ribosomes
II. RNA polymerase catalyses polypeptide synthesis
III. Complementary base pairing between codons and anticodons

A

I and II only

B

I and III only

C

II and III only

D

I, II and III

Exam points

  • Explain that mRNA provides codons while tRNA carries activated amino acids with complementary anticodons.
  • Explain how ribosomes hold mRNA and tRNAs in position so peptide bonds can form.

Question 1

[Maximum number: 7]

Nucleic acids store and transmit genetic information from one generation to the next and regulate the process of protein synthesis.

Explain the role of RNA in translation, resulting in the formation of polypeptide chains.

Exam points

  • Use complementary pairing to match a tRNA anticodon with its mRNA codon.
  • Explain how specific amino acids are attached to their corresponding tRNAs, helping ensure the correct amino acid is added.

Question 1

[Maximum number: 1]

A DNA triplet on the strand that is transcribed has the bases TAG. Which anticodon on tRNA is used in translation?

A

AUC

B

UAG

C

TAG

D

ATC

Exam points

  • Read nucleotide sequences in triplets and relate each mRNA codon to an amino acid or a start/stop signal.
  • Explain degeneracy by identifying different codons for the same amino acid and recognizing why some base changes leave the amino-acid sequence unchanged.
  • Recognize that the genetic code is almost universal and interpret rare exceptions.

Question 1

[Maximum number: 1]

The table shows information on the genetic code of four different mRNA sequences. Which sequence demonstrates degeneracy in the genetic code?

mRNA sequence

Amino acids

UUU UUA UCU

Phe Leu Ser

CUU CCU CUU

Leu Pro Leu

AUG ACG AAG

Met Thr Lys

GUU GGU GUG

Val Gly Val

Exam points

  • Convert a template-DNA sequence to its complementary mRNA sequence before consulting the genetic code table.
  • Read mRNA codons in the 5′→3′ direction and use the genetic code table to identify the corresponding amino acids.
  • Check a complete DNA→mRNA→polypeptide representation and justify the resulting amino-acid sequence.

Question 1

[Maximum number: 1]

The table shows the genetic code.

2nd base in codon

2nd base in codon

Which mRNA could code for the sequence Ser-Leu-Arg-Phe?

A

UCA UCG UGG UUU

B

UCC ACC AGA UUC

C

UCU CCC AGA UUU

D

UCG CUG AGG UUC

Exam points

  • Explain how ribosome movement along mRNA adds amino acids one by one, so ribosomes at different stages carry polypeptides of different lengths.

Question 1

[Maximum number: 2]

Six polypeptides are shown in the diagram. Explain the different lengths of these polypeptides.

Exam points

  • Identify a base substitution and the resulting change in a DNA triplet or mRNA codon for beta-haemoglobin.
  • Relate the altered codon to replacement of glutamic acid by valine and a changed haemoglobin primary structure.
  • Explain how altered haemoglobin structure changes red-cell shape and oxygen transport in sickle-cell anaemia.

Question 1

[Maximum number: 1]

Hemoglobin is a protein made up of two alpha and two beta polypeptide chains. In sickle cell anemia, a mutation causes one glutamic acid in each beta chain to be replaced by valine, as shown in the image.

Normal beta chain

Normal beta chain

Sickle beta chain

Sickle beta chain

How does this mutation in hemoglobin cause sickle cell anemia?

A

It prevents the beta chains from forming a protein.

B

It replaces an amino acid with a fatty acid in the beta chain.

C

It changes the three-dimensional conformation of hemoglobin.

D

The polypeptide produced in sickle hemoglobin is shorter than in normal hemoglobin.