C485 Exam III Fall ‘14
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. (8 Pts) What are the requirements for biological nitrogen fixation in terms of
electrons/nitrogen molecule and ATP consumed /nitrogen molecule fixed. Does the
reaction require the same amount of electrons as chemical fixation? If not, how do these
numbers differ and why are they different?
2. (12 pts) List the 20 amino acids under the correct heading (name or structure).
Glucogenic
Ketogenic
Both
3. (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.
4. (16 pts) Outline the full biosynthetic pathway for leucine. 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. (12 pts) Outline the biosynthesis of methionine showing all products and reactants.
YOU MUST USE STRUCTURES. What cofactors/cosubstrates are required for the
transfer of the methyl group onto methionine? Be specific. Draw the mechanism for the
penultimate (next to last) step of the pathway.
6. (12 pts) Outline the degradation pathways for proline and histidine.
.
7. (12 pts) There are two different pathways (one step vs three steps) that may be used
for the synthesis of glu in the liver. Please show them. (Do not use transamination.)
What are the energetic requirements of these reactions? Why are there two pathways?
Normally, which direction do you think the shorter pathway runs in in the liver? What
about in bacteria?
8. (12 pts) Phenylketonuria is an enzymopathy that makes it impossible for people to
degrade phenylalanine. What enzymatic step is affected? Draw the mechanism of this
reaction. Outline the rest of the degradative pathway.
9. (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.
10. (10 pts) extra credit The shikimate pathway converts carbohydrates into carbocycles
and then into aromatic rings. Outline 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.
11. (8 pts) extra credit Outline glycine degradation. Please draw the mechanism(s) for
this transformation, showing all required cofactors and their recycling.
Point breakdown
Possible
actual
1)
8
________
2)
12
________
3)
12
________
4)
16
________
5)
12
________
6)
12
________
7)
12
________
8)
12
________
9)
6
________
10)
10
________
11)
8
________
TOTAL 120
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