Gene control by transcription factorsEdexcel A-Level Biology A: Subtopic test

1. 1
   A researcher compares a liver cell and a skeletal muscle cell taken from the same person. Both cells contain exactly the same genome, but the two cells make very different sets of proteins.

   (a)

   Which statement best explains why the liver cell and muscle cell make different proteins?

   [1 mark]

   • AThey contain different DNA base sequences
   • BDifferent genes are transcribed because different transcription factors are active
   • CThe liver cell has lost the genes for muscle proteins
   • DTheir ribosomes read the same mRNA in different ways

   (b)

   Where on a gene do many transcription factors bind to affect the rate of transcription?

   [1 mark]

   • AThe promoter region of the DNA
   • BThe anticodon of tRNA
   • CThe codons of the mRNA
   • DThe large subunit of the ribosome

   (c)

   Explain how a transcription factor can switch on a gene.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Oestrogen is a steroid hormone that stimulates cells lining the uterus to make particular proteins. Oestrogen is lipid-soluble and acts by entering its target cells.

   (a)

   Why can oestrogen pass directly into its target cells?

   [1 mark]

   • AIt is a protein and is taken in by endocytosis
   • BIt binds to a channel protein in the membrane
   • CIt is a large polar molecule that diffuses between phospholipids
   • DIt is lipid-soluble, so it diffuses through the phospholipid bilayer

   (b)

   What happens after oestrogen has entered a target cell?

   [1 mark]

   • AIt binds to a cell-surface receptor and starts a signalling cascade
   • BIt binds to ribosomes and speeds up translation
   • CIt binds to a receptor and the complex acts as a transcription factor that binds to DNA
   • DIt is broken down by enzymes in the cytoplasm so it can enter the nucleus

   (c)

   Explain why oestrogen affects only certain cells in the body.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A scientist grows human cells in culture and measures the amount of mRNA made from gene X, in arbitrary units, after 6 hours. Cells with no oestrogen contained 4 units. Cells given oestrogen contained 52 units. Cells given oestrogen together with a drug that blocks the oestrogen receptor contained 5 units.

   (a)

   Calculate the percentage increase in mRNA from gene X caused by oestrogen alone.

   [3 marks]

   (b)

   Explain these results.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A sports scientist is investigating how the steroid hormone testosterone increases the production of muscle proteins in skeletal muscle cells. Some athletes take synthetic anabolic steroids, which have a similar structure to testosterone, to gain a performance advantage.

   (a)

   Explain how testosterone can bring about an increase in the production of muscle proteins in a skeletal muscle cell.

   [6 marks]

   (b)

   Explain why a cell does not express all of its genes and how transcription factors can both switch genes on and switch genes off. Suggest why anabolic steroids can affect tissues other than muscle.

   [6 marks]

   Total for question 4: 12 marks

End of questions