Hormones and gene expressionEdexcel International A Level Biology: Subtopic test

1. 1
   A student compares how two hormones affect their target cells. Insulin is a peptide hormone released by the pancreas, and oestrogen is a steroid hormone released by the ovaries. Both hormones travel in the blood to all parts of the body.

   (a)

   Why can oestrogen enter its target cells directly, while insulin cannot?

   [1 mark]

   • AOestrogen is a protein, so it enters through channel proteins
   • BInsulin is lipid-soluble and is too large to enter
   • COestrogen is hydrophilic, so it enters through aquaporins
   • DOestrogen is lipid-soluble, so it diffuses through the phospholipid bilayer

   (b)

   Where is the receptor for oestrogen located in a target cell?

   [1 mark]

   • AIn the cell-surface membrane
   • BInside the cell, in the cytoplasm or nucleus
   • COn the outer surface of ribosomes only
   • DIn the cell wall

   (c)

   Explain why only certain cells respond to insulin, even though every cell in the body is exposed to it.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In liver cells, a gene codes for an enzyme that is only made when the cell is exposed to a particular hormone. Researchers find that the gene is switched on only when a transcription factor is bound to a specific region of DNA next to the gene.

   (a)

   Where does a transcription factor bind to switch on a gene?

   [1 mark]

   • ATo the promoter region of the DNA next to the gene
   • BTo the ribosome that will translate the gene
   • CTo the mRNA after it has been made
   • DTo the active site of the enzyme the gene codes for

   (b)

   What does the binding of an activating transcription factor allow to happen?

   [1 mark]

   • ADNA to be replicated before the cell divides
   • BRibosomes to read the DNA directly
   • CRNA polymerase to bind and transcribe the gene
   • DThe gene to be deleted from the DNA

   (c)

   Explain how the binding of the transcription factor can result in the liver cell making more of the enzyme.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Researchers add radioactively labelled hormones to isolated liver cells. After a few minutes, labelled glucagon (a peptide hormone) is found only on the cell-surface membrane. Labelled cortisol (a steroid hormone) is found inside the nucleus. When the cells are also given a chemical that inhibits RNA polymerase, cortisol no longer causes the cells to make a new enzyme, but glucagon still causes the cells to release glucose within seconds.

   (a)

   Explain why labelled glucagon is found only on the cell-surface membrane but labelled cortisol is found in the nucleus.

   [3 marks]

   (b)

   Suggest why the inhibitor of RNA polymerase stops the effect of cortisol but not the effect of glucagon.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A company tests two new drugs on cultured cells. Drug A is a peptide hormone analogue and drug B is a steroid hormone analogue. Drug A causes a response within seconds without any new protein being made. Drug B switches on the gene for protein P after several hours. Drug B has an effect on liver cells but none on muscle cells, although both cell types contain identical DNA.

   (a)

   Explain the differences in the way that drug A and drug B act on the cells.

   [6 marks]

   (b)

   Explain how drug B can switch on the gene for protein P in liver cells but have no effect in muscle cells, even though both cell types contain identical DNA.

   [6 marks]

   Total for question 4: 12 marks

End of questions