C483 Fall 2015
Exam 3
Name ______________________________________________
1. 20 pts Fill in the blanks (2 points each)
A. Hexokinase locks glucose into the cell by transforming it into _________________________.
B. ____________________________________ is the most potent allosteric effector of
phsophofrucotkinase.
C. The transformation of pyruvate to oxaloacetate requires the cofactor ____________________.
D. The heavily regulated enzyme responsible for glycogen breakdown is called
_______________________________________.
E. When glucose-6-phophate is run through the oxidative stage of the pentose phosphate
pathway, two molecules of ________________ are produced, as well as a five carbon sugar.
F. A negative change in standard reduction potential means that a compound will
________________________ (spontaneously/not spontaneously) accept electrons under standard
conditions.
G. Complex I catalyzes transfer of high energy electrons from _____________ to ____________
through a series of redox centers.
H. The binding change mechanism of ATP synthase is based on conformational changes of
subunits from open to _____________ to _______________.
I. The main regulation point of fatty acid synthesis is at the enzyme ______________________,
which is _____________________(inhibited/activated) by citrate.
J. High levels of acetyl CoA in the matrix lead to formation of __________________, which are
water-soluble fuels that can be used by the brain in starvation.
2. 10 points True or false (1 point each)
A. ______________ Aldolase catalyzes a reaction with a large positive standard free energy, making the
reaction unfavorable under physiological conditions.
B. ______________ The transformation of pyruvate to phosphoenolpyruvate requires the hydrolysis of 2
ATP equivalents.
C. ______________ Incorporation of a molecule of glucose into glycogen costs two ATP equivalents.
D. ______________ The non-oxidative phase of the pentose phosphate pathway is a reversible
transformation of 5-carbon sugars into 3- and 6-carbon sugars, and vice versa.
E. ______________ The pyruvate dehydrogenase complex requires 5 cofactors to transform acetyl CoA
into pyruvate.
F. ______________ Complex II of the electron transport chain, also called succinate
dehydrogenase, forms QH2 but does not transport any protons.
G. _______________ Uncouplers are respiratory poisons because they inhibit the flow of electrons
through the electron transport chain.
H. _______________ Q differs from NAD+ as a redox reagent because it can donate/accept one electron
at a time.
I. ________________ Fatty acid synthesis and degradation differ in their required cofactors; degradation
requires both Q and NAD+, but synthesis requires only NADH.
J. ________________ The carbon source for the biosynthesis of cholesterol is acetyl CoA.
3. (20pts) Short answer (5 points each)
A. The reactions below are part of the pentose phosphate pathway. Fill in the table with the type
of enzyme is needed to catalyze each reaction: dehydrogenase, epimerase, isomerase,
transaldolase, or transketalase. If a cofactor is required, write the name of the cofactor, or write
“none.”
Reaction
enzyme
cofactor
B
F
H
B. Write the net equation (ignoring water and protons) for gluconeogenesis starting from
pyruvate.
C. Starting with one molecule of pyruvate, how many ATP could be obtained by catabolism
through the citric acid cycle under aerobic conditions? Show work.
D. Use the data provided at the end of the exam to calculate the standard free energy change for the
reaction catalyzed by phosphoglycerate kinase. (The starting material for this reaction is 1,3bisphosphoglycerate.)
Problems (10pts each)
4. A. The reaction for the activation of fatty acids to fatty acyl-CoA, with concommittal hydrolysis of
ATP to AMP and pyrophosphate has a standard free energy change of about zero, but it is driven by a
subsequent hydrolysis of pyrophosphate. Write the equation for the coupled reaction, and calculate the
standard free energy of the reaction using data on the last page.
B. Would you expect the concentration of reactants or products to be greater once this reaction reaches
equilibrium at 298 K? Calculate the equilibrium constant for the coupled reaction.
5. A. Provide a full, enzyme-catalyzed arrow mechanism of glyceraldehyde-3-P dehydrogenase,
including the role of the active site cysteine residue. The structure of NAD+ is provided.
B. Arsenate is a phosphate analog and can replace phosphate in the GAPDH reaction. The
product is unstable and spontaneously hydrolyzes. What is the effect of arsenate on cells
undergoing glycolysis under anaerobic conditions?
6. Draw the structures of the 8 intermediates of the citric acid cycle. Which reactions produce
carbon dioxide? Which produce reduced cofactors? Which produce substrate level high energy
bonds?
Write the overall reaction equation of the citric acid cycle.
7. Draw a simple schematic of ATP synthase in terms of its F0 and F1 components, including
orientation in the membrane. What is the main function of each component?
Mammalian ATP synthase has 8 c subunits, but a bacterial ATP synthase has 10 c subunits.
What is the theoretical P/O ratio for a bacterial ATP synthase utilizing NADH as an electron
donor? (Assume that the electron transport chain resembles the mammalian electron transport
chain in terms of protons pumped.)
Is bacterial ATP synthase more or less efficient than mammalian ATP synthase?
8. Draw the intermediates and products of the -oxidation of this five carbon acylCoA molecule.
This 5-carbon acyl CoA is said to be glucogenic because it can be used to make net glucose. Give an
outline of the pathway through which net glucose can be made from this compound.
Explain why a 4-carbon acylCoA could not be used to make net glucose.
9. (10pts Case study) Rainbow trout are a good model system for examining muscle metabolism because
it is easy to separate their white muscle, which depends on glycolysis for energy needs, from their red
muscle, which are high in mitochondria and operate oxidatively. In this study, rainbow trout were forced
to swim at 30%, 60%, and 90% of their maximal speed, then their red muscle was tested for pyruvate
dehydrogenase activity and lactate concentrations at 2 minutes, 15 minutes, and 45 minutes for the 90%
speed fish and at 2 minutes, 45 minutes, and 240 minutes in the 30% and 60% speed fish. Graphs for
lactate concentration and PDH activity are shown below. Answer the questions on the next page based on
these data.
Figure 3b
Figure 5
9. A. Figure 5 shows a spike and fall in the activity of PDH in 30% activity fish. Use this data and others
data from the figures to describe the exercise metabolism of 30% activity fish, with reference to aerobic
vs. anaerobic conditions, fuel sources, and metabolic changes over the time course. Explain with specific
references to Figures 3B and 5.
B. Figure 5 shows a spike, but no fall, in the activity of PDH in 90% activity fish. Use this data and others
data from the figures to describe the exercise metabolism of 90% activity fish, with reference to aerobic
vs. anaerobic conditions, fuel sources, and metabolic changes over the time course. Explain with specific
references to Figures 3B and 5.
[𝑋]𝑓𝑖𝑛𝑎𝑙
G = RT ln[𝑋]𝑖𝑛𝑖𝑡𝑖𝑎𝑙 + ZF
R = 8.314 J/ mol . K
F = 96,485 J/V . mol
Go’ = -RT ln Keq
Go’ = -nFEo’