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3.8.2 Gene expression is controlled

AQA A-level Biology 3.8.2 practice on Gene expression is controlled, with free MCQs, clues and worked explanations drawn from the The control of gene expression section of specification 7402.

Specification route
3.8.2
Question bank
37 questions
Course stage
Year 13 / A-level only

Sample questions

QUESTION 1 · 3.8.2.1 · LEVEL 1

Which type of stem cell is found in the early mammalian embryo and has the ability to divide and form any type of body cell?

  • Totipotent cells
  • Pluripotent cells
  • Multipotent cells
  • Unipotent cells
Show clue

The prefix 'toti-' means whole or entire.

Show answer and explanation

Answer: Totipotent cells

Totipotent cells can divide and produce any type of body cell. They only occur for a limited time in early mammalian embryos.

QUESTION 2 · 3.8.2.1 · LEVEL 3

What are induced pluripotent stem cells (iPS cells) produced from?

  • Adult somatic (body) cells using appropriate protein transcription factors.
  • Unfertilised egg cells stimulated by an electrical current.
  • Bone marrow cells exposed to high levels of radiation.
  • Embryonic stem cells treated with specific viral vectors.
Show clue

They are 'induced' (forced) to revert from a specialized state back to a pluripotent state.

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Answer: Adult somatic (body) cells using appropriate protein transcription factors.

Induced pluripotent stem cells (iPS cells) can be produced from adult somatic cells using appropriate protein transcription factors to 'reprogram' them back to a state of pluripotency.

QUESTION 3 · 3.8.2.1 · LEVEL 2

During development, how do totipotent cells become specialised (differentiated)?

  • They translate only part of their DNA, meaning only specific genes are expressed to produce specific proteins.
  • They physically delete the genes they do not need from their genome.
  • They undergo targeted mutations to alter their proteome.
  • They absorb specific mRNAs from the surrounding environment.
Show clue

All cells contain the same DNA, but they don't read all of it.

Show answer and explanation

Answer: They translate only part of their DNA, meaning only specific genes are expressed to produce specific proteins.

During development, totipotent cells translate only part of their DNA, resulting in cell specialisation. Unused genes are switched off and not transcribed or translated.

QUESTION 4 · 3.8.2.2 · LEVEL 3

How do specific transcriptional factors stimulate the transcription of a target gene in eukaryotes?

  • They move from the cytoplasm into the nucleus and bind to a specific base sequence on the DNA, promoting the binding of RNA polymerase.
  • They bind to the mRNA in the cytoplasm to initiate translation at the ribosome.
  • They act as restriction endonucleases, cutting the DNA to expose the gene.
  • They methylate the DNA, physically uncoiling the chromosome.
Show clue

Transcription occurs in the nucleus and requires RNA polymerase.

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Answer: They move from the cytoplasm into the nucleus and bind to a specific base sequence on the DNA, promoting the binding of RNA polymerase.

In eukaryotes, transcription of target genes can be stimulated or inhibited when specific transcriptional factors move from the cytoplasm into the nucleus and bind to specific promoter regions on the DNA.

QUESTION 5 · 3.8.2.2 · LEVEL 4

How does the steroid hormone oestrogen initiate transcription?

  • It is lipid-soluble, diffuses across the cell membrane, and binds to a receptor on a transcriptional factor, changing its shape and causing it to bind to DNA.
  • It binds to a receptor on the cell-surface membrane, triggering a second messenger pathway involving cAMP.
  • It acts directly as RNA polymerase to transcribe the target gene.
  • It physically uncoils the histone proteins, exposing the target gene.
Show clue

Steroid hormones are lipids, allowing them to enter cells directly rather than using surface receptors.

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Answer: It is lipid-soluble, diffuses across the cell membrane, and binds to a receptor on a transcriptional factor, changing its shape and causing it to bind to DNA.

The role of the steroid hormone, oestrogen, in initiating transcription. Oestrogen passes through the cell membrane and binds to a transcriptional factor, altering its shape so it can enter the nucleus and bind to DNA to stimulate transcription.

QUESTION 6 · 3.8.2.2 · LEVEL 1

What is the definition of epigenetics?

  • Heritable changes in gene function, without changes to the base sequence of DNA.
  • Changes in the base sequence of DNA caused by environmental mutagens.
  • The transfer of plasmids between bacteria causing changes in phenotype.
  • The process of crossing over during meiosis that creates new allele combinations.
Show clue

The prefix 'epi-' means above or on top of. It's a layer of control on top of the genes.

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Answer: Heritable changes in gene function, without changes to the base sequence of DNA.

Epigenetics involves heritable changes in gene function, without changes to the base sequence of DNA.

QUESTION 7 · 3.8.2.2 · LEVEL 4

How does increased methylation of DNA inhibit transcription?

  • Methyl groups attach to the cytosine bases of DNA, preventing the binding of transcriptional factors and attracting proteins that condense the DNA-histone complex.
  • Methyl groups physically block the nuclear pores, preventing mRNA from leaving the nucleus.
  • Methyl groups bind to RNA polymerase, causing it to denature.
  • Methyl groups repel the histone proteins, causing the DNA to unravel uncontrollably.
Show clue

Adding methyl groups condenses the chromatin, making the genes inaccessible.

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Answer: Methyl groups attach to the cytosine bases of DNA, preventing the binding of transcriptional factors and attracting proteins that condense the DNA-histone complex.

Changes in the environment that inhibit transcription by: increased methylation of the DNA. Methylation typically occurs at CpG sites, preventing transcription factor binding and recruiting deacetylases that condense chromatin.

QUESTION 8 · 3.8.2.2 · LEVEL 4

What is the effect of decreased acetylation of associated histones on gene expression?

  • It increases the positive charge on histones, causing them to bind more tightly to the negatively charged DNA, preventing transcription.
  • It decreases the positive charge on histones, loosening the DNA and stimulating transcription.
  • It breaks down the histone proteins entirely, leaving the DNA exposed and increasing expression.
  • It causes the DNA to mutate rapidly, leading to the formation of oncogenes.
Show clue

Acetylation usually neutralises positive charges. Decreasing acetylation maintains a strong positive charge, leading to a strong attraction to negative DNA.

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Answer: It increases the positive charge on histones, causing them to bind more tightly to the negatively charged DNA, preventing transcription.

Decreased acetylation of associated histones increases their positive charge, increasing their attraction to the negatively charged phosphate groups of DNA. The chromatin becomes highly condensed (heterochromatin), inhibiting transcription.

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