Chem. 454/96

75 PTS.

NAME .

1. For birds, arginine is an essential dietary amino acid. For humans (except infants) it is not. What does this tell you about the metabolism of birds and why are they this way (metabolic logic)? Be specific.(8)

2. Turnover of proteins is well regulated and different proteins have distinct average life spans. Describe two mechanisms by which the life span of proteins is regulated.(8)

3. Give the structures or names of the aminotransferase products (transaminations) for the following (only where possible!):(15)

a. alanine

b. oxaloacetate

c.

(Give two different possibilities)

d. proline

e.

4. Glutamate can be used to synthesize arginine with the help of the urea cycle. Insert the following metabolic intermediates in their logical places. Insert the names of the most likely additional cofactors and metabolites (e.g. NAD+, NADH, Acetyl CoA, H₂O, ATP, etc) where blanks are present. You do not need to speculate on the enzyme cofactors necessary such as , e.g., pyridoxal phosphate (PLP), biotin, biopterin, vit. B₁₂, etc. (10)

5. Below is the synthetic pathway of phenylalanine and tyrosine from the point of chorismate. Chorismate is also a precursor of tryptophan. Using arrows and X's show a plausible regulatory scheme for this pathway. Then in words describe the reason for the scheme chosen.(10)

6. Leucine is considered a ketogenic amino acid and asparagine is considered glucogenic. Using these amino acids as examples, describe what these terms mean. What are the biochemical implications for a person on a low carbohydrate diet who eats protein rich in one or the other of these amino acids? That is, if one had to live on either on of these amino acids, which would be best and why.(8)

7. Propose a mechanism for the condensation of ornithine with carbamoyl phosphate to obtain citrulline (the first step in the urea cycle). Suggest (show) possible amino acid side chains at the active site which would help catalyze this reaction.(8)

8. Propose a plausible pathway from the enzyme phenylalanine to the important neurotransmitter DOPAMINE. Include all cofactors and reactants including enzyme prosthetic groups like, e.g. O₂, PLP, biotin, FAD, methylene-THF, etc., etc.(8)

BONUS:(2pts) Draw the structure of heme.