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Biochem 462
Second Exam
Multiple choice: each question has only one answer (45%)
The carbon dioxide that we breath out comes mostly from:
a) The conversion of glucose to pyruvate during glycolysis
b) The catabolism of pyruvate through the TCA cycle
c) Oxidative Phosphorylation
d) Electron transport through complex IV
Which of the cofactors involved in the mechanism of the pyruvate dehydrogenase
reaction (conversion of pyruvate to acetyl CoA) actually performs the net oxidation of
pyruvate directly?
b) FADH2
c) TPP
d) Lipoic Acid
Which of the following compounds inhibit the citrate synthase reaction (formation of
citrate from acetyl CoA and oxaloacetic acid):
a) ATP
c) Succinyl CoA
d) All of the above
Half reactions are not real chemical reactions, and yet we assign them an actual
voltage. This is done by
a) Measuring the voltage at just one of the electrodes in an electrochemical cell.
b) Determining the voltage for a standard state in which all components are at 1 M
and the current is at 1 Amp.
c) Measuring the voltage relative to the standard hydrogen electrode.
d) Measuring the voltage by using a mediator to react with electrons that are
produced in the half reaction.
The primary source of reductive potential that is used to power oxidative
phosphorylation is
b) ATP
c) NAD+
d) ADP
A protein that extended through the membrane and was exposed on either side would
be called
a) An integral membrane protein.
b) A peripheral membrane protein.
c) A glycoprotein
d) A lipoprotein
The free energy for moving glucose across a membrane depends on:
a) The relative concentration of glucose on the inside and the outside
b) The membrane potential (the voltage across the membrane)
c) Both the concentration gradient and the membrane voltage
d) The concentration gradient, the membrane voltage and the concentration of ions
on each side of the membrane.
The main thing that distinguishes active diffusion from passive or facilitated diffusion
a) Active diffusion involves movement of molecules across membranes rather than
laterally along the membrane surface.
b) Active diffusion requires the direct consumption of energy during the process of
transporting molecules across the membrane.
c) Active diffusion involves specific recognition of the molecule to be transported
by a receptor protein.
d) Active diffusion requires a transmembrane gradient in order to function.
Most of the ATP generated during the catabolism of glucose to carbon dioxide and
water occurs by
a) Substrate level phosphorylation in glycolysis
b) Substrate level phosphorylation in the TCA cycle
c) Substrate level phosphorylation during the electron transport chain of the
d) Oxidative phosphorylation
The electrons from NADH enter the respiratory electron transport chain at
a) Complex I
b) Complex II
c) Complex III
d) Complex IV
The redox energy stored in NADH is used to drive ATP synthesis during oxidative
phosphorylation. This process can be best characterized by which statement?
a) ATP is generated by electron transfer from quinones to ADP which then reacts
with a phosphate molecule
b) The membrane potential generated during electron transport in the mitochondria
increases the chemical potential of the highly charged phosphate ion which then
reacts with ADP to form ATP
c) The proton gradient formed during electron transport in the mitochondria powers
a molecular turbine whose mechanical energy is used to form ATP from ADP
d) The concentration of protons on one side of the membrane due to proton transfer
during mitochondrial electron transport is large enough to drive the
phophorylation reaction of ADP to ATP (this reaction consumes protons)
Electrons from Complex I are transferred to Complex III by
a) A cytochrome molecule that travels in the lipid membrane interior.
b) A quinone molecule that travels in the lipid membrane interior.
c) A cytochrome molecule that travels through the aqueous environment near the
d) A quinone molecule that travels through the aqueous environment near the
Short Answer (45%)
Draw the intermediate between isocitrate and alpha-ketoglutarate. Also add any
cofactors involved and make sure the reaction is balanced.
While investigating the metabolism of an new species of bacterium you discovered,
you found the following as the beginning and end points of a metabolic chain.
Suggest what intermediates you would likely find between these compounds based on
your understanding of the TCA cycle. Show all cofactors involved and balance the
What is the overall free energy change per mole for pumping sodium ions (Na+) from
the inside to the outside of cells assuming that the concentration of sodium inside the
cell is 20 mM and that outside is 200 mM and that the membrane potential is 150 mV
more positive on the outside of the cells? No other ions can cross the membrane and
the Na+ concentrations and the membrane potential remain constant the whole time.
G = RT ln(out/in) + zF
R = 8.31 J/(K mole), F = 96500 J/(V mole)
Write a balanced equation describing the reaction carried out by complex III in the
mitochondiral respiratory electron transfer chain.
Draw a picture showing how quinones can be used to couple electron transfer to
proton transfer in a membrane. It does not need to be a complicated scheme (you do
not have to reproduce the Q-cycle, for example). I just want you to demonstrate that
you understand how sequential reduction and oxidation of a quinone can resulting in
proton pumping.
Explain in a couple of sentences what determines the number of protons that must
pass through the ATP synthase complex per ATP molecule made.
Quantitative Extension (10%)
a) Assuming that 32 ATP are made by oxidation of glucose, write total, balanced, net
reaction that shows the oxidation of glucose during respiration and formation of ATP.
b) Assuming that the free energy change for generating a mole of ATP from ADP and
phosphate is 50 kJ/mole and that the total free energy change for the complete oxidation of a
mole of glucose by oxygen is about –3000 kJ/mole, calculate the overall free energy for the
reaction in a)