Question

Serotonin is synthesized from the amino acid tryptophan (normal cells can synthesize serotonin when they are given tryptophan). You have identified two populations of mutant cells that cannot synthesize serotonin. Each population has a mutation that has caused one gene to stop functioning. Population 1 cannot synthesize serotonin at all, even if you provide it additional nutrients. Population 2 can synthesize serotonin, but only if you give it a nutrient called 5-HTP.

a. Based on this information, draw a biochemical pathway starting with tryptophan and ending with serotonin. How does 5-HTP fit into this pathway? Be sure to indicate the location of any enzymes.

b. Describe the mutation you expect to see in each population based on your biochemical pathway

Answer 1

1) The production of serotonin from tryptophan:

The enzyme tryptophan hydroxylase reacts to produce 5-HTP from tryptophan and is functional in pineal glands, gut and bones, Raphe nucleus in midbrain. The enzyme L-amino acid decarboxylase converts the 5-HTP to serotonin is found in the trans-Golgi region and the secretory vescicles.

2) The first population of cells cannot produce serotonin at all even in presence of nutrients. This means that the mutation lies in the enzymes that initiate the production. The mutation lies in the L-tryptophan-5-monooxygenase tryptophan hydroxylase enzyme as well as the aromatic amino acid decarboxylase enzyme that takes part in the production of the serotonin by converting the tryptophan to 5-HTP. The second population of cells has a mutation that allows production of the serotonin only if 5-HTP is provided to the medium. This shows that the mutation lies in the specific functional group of the first enzyme but not in the second enzyme. Thus the first step is not applicable but introducing 5-HTP will trigger the second enzyme and there will be serotonin production.