C485 Exam III Fall ‘15
Name______
Legible please!
Do not use acronyms unless instructed to do so. Use structures whenever they are asked for, or appropriate. Your explanations should be brief. Overly lengthy answers with irrelevant or erroneous material will receive deductions. Use the back of the page if you need room. GOOD LUCK
1.(10Pts) Fill in the blank.
a. Uses pyruvate and aspartate for its biosynthesis lysine
b. Uses two pyruvates and an acetyl CoA for its biosynthesis leucine
c. Derives a methyl group via a B-12 mediated transformation methionine
d. Theherbicide roundup (glyphosate) targets this enzyme EPSP synthase
e. Derives one of its carbons from ATP histidine
2. (12 pts) Starting with chorismate, outline the biosynthetic pathway for tryptophan (structures). Make sure to show all products and reactants. Draw the mechanism by which the indole ring is first generated (penultimate step).See last page
3. (10Pts) List the amino acids whose carbon skeletons are derived completely from intermediates in glycolysis (including pyruvate). There are five. Incorrect answers will result in point deduction.
Serine, glycine, alanine, cysteine, valine
4. (12 pts) Outline the full biosynthetic pathway for isoleucine. YOU MUST USE STRUCTURES. Show all products and reactants for each step. Draw the mechanism of the first step. There is also a rearrangement step. Draw the mechanism for that step as well.see last page
5. (6 Pts). Draw and number the structure of histidine. Using your labeling system, draw the precursor molecule(s) for its biosynthesis and show where the heavy atoms of this amino acid are derived from.See last page
6. (10 pts) Tetrahydrobiopterin is a cofactor used for the hydroxylation of aromatic rings. Where is this reaction utilized. Draw the structure of THB and show the mechanism by which it catalyzes such a transformation.See last page
7. (8 pts)How are the biosyntheses of arginine and proline related?
Arginine and proline are synthesized from the same starting source- glutatmate (or -keto glutatrate). Glu is converted in two steps into glutamate semialdehyde, which is an intermediate in both the synthesis of pro and arg. Transamination of this aldehyde yields ornithine, which is converted to arginine via the urea cycle. Cyclization and reduction of this material yields pro. Thus the carbon skeletons of the two amino acids are derived identically.
8. (12 pts) How is the degradative pathway of tryptophan related to the degradative pathway of lysine?Both of these amino acids have a degradation pathway that intersects at-keto adipic acid. From that point, the degradation pathway for both is identical. Oxidative decarboxylation followed by insertion of a double bond and decarboxylation gives a four carbon intermediate that is identical to that found in fatty acid degradation. (must use structures for full credit)
9. (14 pts) Outline the biosynthetic pathway (structures and reagents) for cysteine, starting with two proteinacious amino acids. PLP is involved in a number of these transformations. For each PLP-dependent process, state the nature of the transformation that is being effected (e.g. transamination, or retroaldol, etc.) (Proteinacious amino acids are amino acids normally found in proteins.)see last page
10. (8 pts) Outline the degradation of phenylalanine (structures please).
See last page
11. (8pts) extra credit The shikimate pathway converts carbohydrates into carbocycles and then into aromatic rings. Show the step in the shikimate pathway that produces a carbocyclic ring. Suggest a mechanism for this transformation, considering that the enzyme contains a bound NAD+, yet does not catalyze any overall redox chemistry.
See last page