Research updates
2. New methods of contraception   p 5
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3. A contraceptive pill for men Link to the Medical Research Council web site
 
Another target for contraception in men
The gonadatrophic hormones that regulate sperm production are secreted by the pituitary gland. Secretion is stimulated by a releasing hormone, called gonadotrophin-releasing hormone (GnRH). This acts by attaching itself to specific receptor molecules (GnRH-R) in the cell membrane. Understanding how this interaction can trigger the release of the gonadotrophic hormones could help scientists searching for new approaches to contraception in men.
Figure 6. Click here to enlarge image in a new window.
At the MRC Human Reproductive Sciences Unit, a group directed by Dr Karin Eidne, a biochemist who at that time led the MRC research programme on the pituitary gland, established the structure of the GnRH-R receptor molecule in the 1990s.
The receptor molecule is a protein (with 327 amino acids units) which loops back and forth across the cell membrane (see Figure 6).
Professor Robert Millar has continued the research into the GnRH-R receptor. His group is investigating another approach to contraception in which gonadotrophin secretion is suppressed by introducing a substance which binds to the site on the receptor in place of the releasing hormone.
name abbrev'n nature
of chain
glycine gly G non-polar
alanine ala A non-polar
valine val V non-polar
leucine leu L non-polar
isoleucine lie I non-polar
proline pro P non-polar
tryptophan trp W non-polar
methionine met M non-polar
phenylalanine phe F non-polar
serine ser S polar
threonine thr T polar
cysteine cys C polar
asparagine asn N polar
glutamine gln Q polar
tyrosine tyr Y polar
histidine his H basic
arginine arg R basic
lysine lys K basic
aspartic acid asp D acidic
Table 1.

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Question 5

Use Figure 6 together with Table 1, which shows the one letter codes for amino acids. Click here to open a new window with an enlarged Figure 6.

a) Count the number of non-polar and polar amino acids in each of the separate sections of the protein which is within the lipid bilayer. Record your values in a suitable table and calculate the ratio of non-polar:polar amino acids.

lipid bi-layer
non-polar polar ratio

b) Repeat this process for each of the sections of the protein which lie outside the lipid bilayer.

inside cell
non-polar polar ratio

outside cell
non-polar polar ratio

c) How does the ratio of non-polar:polar amino acids differ between a) and b)? Explain why this might be the case.