C483 Exam 3 2014 answers
1) 10 pts What are the main purposes of the citrate/pyruvate shuttle? Please draw
the reactions of this shuttle.
AcCoA is not membrane permeable. To bring AcCoA to the cytosol for FA synthesis,
it must be piggy-backed on citrate. The ensuing reactions also convert NADH to
NADPH, which is required because the pentose phosphate pathway generates
insufficient NADPH for fatty acid synthesis (about half what is needed).
Citrate + ATP + CoASH converted to OAA + AcCoA + ADP + Pi
OAA + NADH +H+ coverted to malate + NAD
Malate + NADP+ converted to pyruvate + carbon dioxide + NADPH
(you should know these structures!)
2) 20pts total Starting with butanoic acid (C-4) diagram the reactions of its
breakdown via beta-oxidation (structures please). How many ATP’s may be
generated by complete conversion of this molecule to carbon dioxide (details
please)? Consider pentanoic acid. After one cycle of oxidation, there is a remnant
that is converted into a Krebs cycle intermediate. Please diagram this conversion
(structures please) and draw the mechanism of both reactions involved.
22 ATP generated. 10 for each AcCoA through the Krebs cycle. Four from the NADH
(2.5) and QH2 (1.5). Subtract two for activation.
The remnant is propionyl CoA. This is converted in two steps into succinyl CoA by
propionyl CoA carboxylase (Biotin-dependent carboxylase) and methylmalonyl CoA
mutase ( Adenosyl cobalamin-dependent radical rearrangement). You should have
the mechanisms for both in your notes.
3) 6 pts What are the major differences between fatty acid oxidation and synthesis?
Synthesis in cytosol, degradation in mitochondria
Synthesis uses malonyl CoA (C-3) where degradation yields AcCoA
Synthesis uses NADPH
All intermediates covalently bound in synthesis
Synthesis enzyme has all functions in one polypeptide
Synthesis specifically makes a C16 fatty acid. Degradation uses fatty acids of all
sizes.
4) 8 pts Draw the mechanism for the transaldolase reaction in the pentose
phosphate pathway.
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http://en.wikipedia.org/wiki/File:Transaldolasemech.jpg you didn’t need to specify
the nature of enzyme acids and bases
5) 8 pts Draw the mechanism for a transketolase reaction in the pentose phosphate
pathway.
http://en.wikipedia.org/wiki/Transketolase you didn’t need to specify the nature of
enzyme acids and bases
6) 8 pts What is meant by reciprocal regulation? Give an example of this from
glycolysis and gluconeogenesis and from glycogen breakdown and synthesis.
When a molecule, hormone, or enzyme regulates the activity of opposing pathways
by activating one and inhibiting the other.
Glycol vs. gluconeog: fructose 2,6-bisphosphate and AMP both inhib gluconeog,
while activating glycolysis
PKA (as well as hormone glucagon and epinephrine) activate glycogen breakdown
and inhibit glycogen synthesis
7) 4 pts Gluconeogenesis requires four enzymes that are not enzymes of the
glycolytic pathway. These four enzymes are: (If you don’t know the enzymes, just
draw the complete reactions using structures.)
Pyrouvate carboxylase
PEP carboxykinase
Fructose 1,6-bisphosphatase
glucose 6- phosphatase
8) (2 pts each, 12 pts total) Answer the following short answer questions
(acronyms okay)
a) The protein attached to the glycogen primer required for glycogen synthesis is
calledglycogenin
b) In mammals, the hormone epinephrine activates glycogen degradation in the
muscles while insulinactivates glycogen synthesis.
c) The oxidation of succinate uses the enzyme-bound conenzyme flavin adenine
dinucleotide hydride (reduced flavin) due to the need for a stronger oxidizing agent
than NAD+
d) Certain citric acid cycle intermediates serve as bioxynthetic precursors of other
materials. Two such intermediates are oxaloacetate and alpha-ketoglutarate
e) The two mobile electron carriers in oxidative phosphorylation are ubiquinol and
cytochrome C
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f) In the biosphere, the two major sources of nitrogen ultimately used for amino acid
synthesis are: nitrogen and nitrate
9. (2 pts each, 10 pts total) True or false
a) ___f___Each of the 20 common amino acids can be described as being either
glucogenic or ketogenic.
b) ___t_____Saturated fats yield more calories per gram than glucose.
c) ___f_____ Synthesis of fatty acids occurs by addition of 3 carbons per cycle to the
growing fatty acyl group since all three carbons of malonyl CoA are added.
d) ___t_____ The carbon atoms of the ring structure of cholesterol are all derived from
acetyl CoA.
e) ____f_____Protons are pumped across the inner mitochondrial membrane by
complexes I, II and IV during electron transport.
10. (2pts each, 10 pts total) Fill in the blank (acronyms okay)
a) A transaminase enzyme would convert alanine to pyruvate___ while converting
alphaKG to glutamate
b) One of the nitrogen atoms and the carbon atom of urea enter the urea cycle as a
single molecule, namely carbamoyl phosphate (or draw structure)
c) The molecules known as ketone bodies areacetone, acetoacetate, beta-hydroxy
butyrate (or draw structures)
d) The key regulatory enzyme of fatty acid synthesis isAcetyl CoA carboxylase.
Phosphorylation of this enzyme causes inactivation of the enzyme.
e) Phosphatidic acid is activated for conversion to a phospholipid by reaction with
CTP
11. 6 pts Draw the mechanism of succinyl CoA synthetase (fig 13.12 in your book).
See figure 13.12, or your discussion section questions
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12. 5 pts Outline how the Q cycle works. Show the stoichiometry of proton
pumping. The two cycles are shown in figure 14.16. You did not have to show the
intermediate electron carriers.
Extra credit 15 pts. Each error costs 3 pts.
State whether these reactions are oxidations, reductions, or neither. State how
many electrons are involved.
a) 3pts 8 e reduction
b)3 pts 8 electron oxidation
c)3pts 6 electron oxidation
d)3 pts 4 electron oxidation
e) 8 electron reduction
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Points
Possible
earned
1)10
________
2)20
________
3)6
________
4)8
________
5)8
________
6)8
________
7)4
________
8)12
________
9)10
________
10)10
________
11)6
________
12) 5
________
EC15
________
Total 122
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