C485 Exam III Fall ‘12
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. (12pts) The urea cycle is fairly intensive in its use of ATP. Diagram (structures and
equations) the steps of the cycle that use ATP. Make sure you show the fate of the ATP.
3. (6pts) What are the two major (multicarbon) degradation products of tyrosine?
(structure or name acceptable)
4. (6 pts) Which of the following are intermediates in the pathway for the biosyntheiss of
both phenylalanine and tryptophan? circle your answer(s)
(a) Indole
(b) chorismate
(c) dehydroquinate
(d) prephenate
5. (12 Pts) Unlike most organs, muscle uses three specific amino acids as energy sources.
What are these amino acids (structures)? Choose one and draw its degradation pathway.
6. (14 pts) The biosynthetic pathways for tryptophan and cystathionine utilize a betaelimination/beta addition process for their synthesis.
1- What is the amino acid that undergoes elimination in each case?
2- What is the component that adds in each case?
3- Pick one of these processes and draw the mechanism of elimination, starting from the
relevant PLP-adduct. You do not have to show cleavage of the final product from PLP.
7. (10 pts) By what two reactions is ammonia assimilated into amino acids? (Structures
and equations please).
8. (12 Pts) Draw the pathway used for the biosynthesis of valine. Show starting
molecule(s) and all stable intermediates. Note the participation of any cofactors in
specific steps. Show the mechanism (curly arrows and structures please) of the first step
of the pathway.
9. (10 Pts). Draw the structure of tryptophan and itemize the source of each heavy atom.
10. (10Pts) Match the amino acid with its breakdown product (breakdown may be used
more than once).
Threonine _____
A Acetyl CoA
Glycine________
B Pyruvate
Alanine_________
C alpha-keto glutarate
Histidine_________
D alpha-keto butyrate
Lysine___________
E N5,N10-methylene THF
11. (10 pts) The biosynthesis of cysteine employs a gamma-elimination from
cystathionine. Draw this reaction and draw the mechanism of all relevant steps starting
from the cytasthionine-pyridoxal adduct.
Point breakdown
Possible
actual
1)
8
________
2)
12
________
3)
6
________
4)
6
________
5)
12
________
6)
14
________
7)
10
________
8)
12
________
9)
10
________
10)
10
________
11)
10
________
TOTAL 110
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