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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. The herbicide 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. (8 pts) 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