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D1.2.4—Transcription for gene expression

Transcription controls gene expression by producing mRNA only from genes activated in particular cells, tissues, stages or environmental conditions within organisms.

Syllabus
First assessment 2025
Objective
D1.2.4
Level
HL

Exam analysis

Chance of appearing3%of analysed past papers
Latest appearanceMay 2019
Most common paperPaper2
Typical marks1–2

Common command terms

  • Determine
  • Outline
  • Compare
  • Deduce
  • Evaluate

Scoring notes

Common mistake
Treating a visible mRNA band as protein evidence rather than evidence of transcription.

Recent exam appearances

May 2019Paper2 ["HL"] · TZ21(d)[ 1 ]D1.2.4—Transcription for gene expression
May 2017Paper2 ["HL"] · TZ21(f)(iii)[ 2 ]D1.2.4—Transcription for gene expression
May 2017Paper2 ["HL"] · TZ21(f)(ii)[ 2 ]D1.2.4—Transcription for gene expression
May 2017Paper2 ["HL"] · TZ11(e)[ 2 ]D1.2.4—Transcription for gene expression
Practice this objective

Coverage 2017–2019 · Updated 16 Jul 2026

Transcription Turns Gene Information into a Message

Transcription is the first stage of gene expression and a key point at which expression can be switched on or off.

Cells contain many genes but do not express all of them at the same time. If a gene is not transcribed, its mRNA is unavailable for translation; starting transcription makes expression possible.

Regulatory state → transcription on/off → mRNA absent/present → translation possible/not possible. Different cell types express different subsets of the same genome.

A cell can switch on transcription of an enzyme gene when the enzyme is needed while other genes remain untranscribed.

Transcriptional control is a key switch, not the only possible control. More mRNA does not guarantee proportionally more protein if later steps are limiting.

Transcription for gene expression

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through structured response, commonly using Determine / Outline / Compare.

Command terms

Determine / Outline / Compare / Deduce / Evaluate

What earns marks

Build the answer around this relationship: mRNA presence indicates that a gene has been transcribed.

Watch for

Treating a visible mRNA band as protein evidence rather than evidence of transcription.

Representative question

Question 1

[Maximum number: 2]

The scientists concluded that auxin activates the transcription of the GH 3 gene. Using the information on the auxin concentration in the stem base in the graph on page 4 and the Northern blot, evaluate whether this conclusion is supported.

Core Protein Synthesis

  • Transcription: RNA polymerase builds complementary mRNA from the DNA template; A pairs with U and C with G.
  • Translation: ribosomes read mRNA codons 5′ to 3′ while tRNA anticodons deliver specific amino acids for peptide-bond formation.
  • Genetic code: codons are triplets; the code is degenerate and almost universal, with start and stop signals. Use mRNA—not DNA—when reading a code table.
  • Information flow: codon order determines amino-acid sequence, which determines protein folding and function.
  • Expression and variation: cells regulate which genes are transcribed. A mutation may change a codon, primary structure and phenotype, as in sickle-cell haemoglobin.

Concept essentials

  • mRNA presence indicates that a gene has been transcribed.
  • Different cells can express different genes from the same genome.
  • Gel bands and expression graphs can compare transcription across tissues or treatments.
  • Gene expression evidence must be linked to the named gene and condition.