Human prolactin (hPRL) is a globular protein. It is a single polypeptide composed of 199 amino acids. The protein is transported in the bloodstream and has an effect only on cells that have a cell surface membrane protein known as PRLR. One effect of hPRL is to stimulate cells in the mammary glands to produce breast milk. Cells that have been stimulated by hPRL need more glucose and therefore the passive uptake of glucose increases.

1. (a)State one reason why the cells in the mammary glands that have been stimulated by hPRL need more glucose.[1]
2. (b)An experiment was carried out to investigate the movement of glucose and hPRL across Visking tubing membrane. • A short section of Visking tubing, tied at both ends and containing distilled water, was placed into a beaker containing a solution of glucose and hPRL. • After 20 minutes, separate samples of the solution in the Visking tubing and the solution in the beaker were each tested for the presence of protein and reducing sugar. A summary of the methods used, the experimental results and the deductions made are shown in Table 5.1. [Table 5.1] method used sample colour obtained after testing deduction solution in Visking tubing biuret solution added to sample protein absent from solution in Visking tubing solution in beaker protein present in solution in beaker solution in Visking tubing Benedict's solution added to sample and mixture heated in a water-bath reducing sugar present in solution in Visking tubing solution in beaker reducing sugar present in solution in beaker
3. (b)(i)Complete the column in Table 5.1 headed colour obtained after testing.[2]
4. (b)(ii)With reference to the deductions made in Table 5.1, explain the movement of hPRL and reducing sugar across Visking tubing membrane.[2]
5. (c)Outline how glucose crosses the cell surface membranes of the cells of the mammary glands.[2]
6. (d)The production of milk by the cells of the mammary glands involves the action of several different enzymes. The cell surface membranes of these cells contain the membrane protein PRLR. Fig. 5.1 shows an outline summary of hPRL involvement in the production of breast milk. [Figure 5.1] Explain why the production of breast milk can be described as an example of a cell signalling process.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.