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 ____________
b. Uses two pyruvates and an acetyl CoA for its biosynthesis ____________
c. Derives a methyl group via a B-12 mediated transformation _______________
d. The herbicide roundup (glyphosate) targets this enzyme _______________
(or show substrates)
e. Derives one of its carbons from ATP ______________
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).
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.
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.
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.
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.
7. (8 pts)How are the biosyntheses of arginine and proline related?
8. (12 pts) How is the degradative pathway of tryptophan related to the degradative
pathway of lysine?
.
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.)
10. (8 pts) Outline the degradation of phenylalanine (structures please).
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.
Point breakdown
Possible
actual
1)
10
________
2)
12
________
3)
10
________
4)
12
________
5)
6
________
6)
10
________
7)
8
________
8)
12
________
9)
14
________
10)
8
________
11)
8
________
TOTAL 110
________