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Transcript
Name_____________KEY__________________
Student No._________________________________
BCMB 3100 Fall 2013 Exam III
1. (10 pts.) (a.) Briefly describe the purpose of the glycerol dehydrogenase phosphate shuttle.
(b.) How many ATPs can be made when electrons enter the electron transport chain via this
shuttle? Explain your answer.
(a.) The purpose of the glycerol phosphate dehydrogenase shuttle is to pass electrons from
cytosolic NADH (produced by glycolysis) into the mitochondrial electron transport system.
This is done via FAD to FADH2 and from FADH2 to Q.
(b.) Since the electrons enter at Q and into complex III, by-passing complex I, there is a net
transfer of six protons across the membrane and since 4 protons are required to synthesize
and transport one ATP there would be 6/4 or 1.5 ATP molecules per NADH entering via
this shuttle.
2. (8 pts; 4 for part (a) and 4 for part (b)) Peter Mitchell formulated the chemiosmotic theory
based on an experiment in which he measured the consumption of oxygen by mitochondria in the
presence of NADH (substrate) and the addition of ADP, or 2,4-dinitrophenol; the results are
shown below. Briefly state (a.) the chemiosmotic theory, and (b.) how the results of this
experiment supports this theory.
(a.) The chemiosmotic theory proposed that the mitochondrial enzyme complex generates a
proton gradient across the membrane which provides energy for ADP phosphorylation.
(b.) First, the substrate (e.g. NADH) in the presence of mitochondria and with the addition of
ADP stimulate the consumption of O2 until the ADP is all utilized. However when
uncouplers, such as 2,4-dinitrophenol, are membrane-soluble compounds which allow
the unrestricted transfer of protons across the mitochondrial membrane, thereby
destroying the proton gradient. Thus, it was concluded that a proton gradient is required,
i.e. coupled, for the conversion of ADP to ATP.
Name_____________KEY__________________
Student No._________________________________
3. (10 pts.) If actively respiring mitochondria are exposed to an inhibitor of ATP synthase, the
electron transport chain ceases to operate. Why?
The proton gradient cannot be dissipated by flow through ATP synthase. It becomes large
enough that the energy released by the ETC is insufficient to pump protons across the
membrane and electron transport ceases.
4. (12 pts.; 8pts. for part “a” and 4 pts. for part “b”.) (a.) On the diagram below place the
following components of photosynthetic transport in their correct location.
A.
B.
C.
D.
E.
F.
G.
H.
Ferridoxin-NADP+ reductase
P700
OEC or Mn center
P700*
P680
Plastocyanin (Pc)
P680*
Cytochrome bf
D
G
Cyclic electron
transport
A
H
(b.) On the diagram show what
happens during cyclic electron
transport, and give the purpose
of cyclic electron transport.
F
B
C
E
Cyclic electron transport
occurs at high
NADPH/NADP+ ratios where there is insufficient NADP+ to accept the electrons.
5. (10 pts; 8 for (a) and 2 for (b)) (a.)
Calculate the E’o and Go’ for the reduction
of NADP+ by ferridoxin; i.e. for the reaction:
(Faraday’s Const. = 96.5 kJ/mol/V)
NADP+ + Fdred → NADPH + Fdox
Go’ = -zFE’o
E’o = -0.32 -(-0.43) = 0.11V
Go’ = -2(96.48kJ/mole/V)(0.11V) =
-21.2kJ/mole
(b.) Why does ferridoxin-NADP+
oxidoreductase have FAD as a co-factor?
FAD is necessary to accept electrons one at a
time from the oxidoreductase and deliver them
two at a time to NADP+ to give NADPH.
Name_____________KEY__________________
Student No._________________________________
6. (10 pts; 6 pts for (a.) and 4 pts for (b.)) (a.) Describe the stages of the Calvin cycle and the
purpose of each stage. (b.) Draw the reaction (structures of reactants and products) of the
RUBISCO reaction for the Calvin cycle.
(a.) Oxidation: Combines CO2 with ribulose-1,5-bisphosphate to make 3-phosphoglycerate.
Reduction: Conversion of 3-phosphglycerate to glyceraldehyde-3-phosphate which is used
for glucose synthesis and for synthesis of more ribulose-1,5-bisphosphate.
Regeneration: The regeneration of ribulose-1,5-bisphosphate from glyceraldehyde-3phosphate.
(b.)
CH 2OPO3
-2
CH 2OPO3
O
H
OH
H
OH
CH 2OPO3
+
CO 2
H
-2
OH
COOH
-2
7. (10 pts.) Use the following molecules to draw the structure of a phospholipid: Glycerol,
serine, tetradecanoic acid, and C18:111 (place tetradecanonic acid at C1 and C18:111 at C2
of the phospholipid).
8. (10 pts.) Match the following with regard to transport and signal transduction mechanisms:
A.
B.
C.
D.
E.
F.
G.
H.
I.
Active Transport
cAMP
Uniport
Symport
Vesicle
Protein kinase
Antiport
Passive transport
G-protein
J. Adenylate cyclase
__H____down a concentration gradient
__D____two molecules in samedirection
__I____transducer
__C____one molecule in one direction
__A____saturable and requires energy
__E____endocytosis
__B____second messenger
__J____effector enzyme
__G____two molecules in opposite
directions
__F___cytoplasmic factor
Name_____________KEY__________________
Student No._________________________________
9. (8 pts.) Place the following list of reactions or relevant locations in the b oxidation of fatty
acids in the proper order. (Problem Chapter 27)
(a) Reaction with carnitine.
(b) Fatty acid in the cytoplasm.
(c) Activation of fatty acid by joining to CoA.
(d) Hydration.
(e) NAD+-linked oxidation.
(f) Thiolysis.
(g) Acyl CoA in mitochondrion.
(h) FAD-linked oxidation.
b, c, a, g, h, d, e, f
10. (12 pts; 7 for part (a.) and 5 for
part (b.) (a.) Match the following
with regard to the synthesis of fatty
acids.
A.
B.
C.
D.
E.
F.
G.
Enoyl reductase
Malonyl transacylase
-Ketoacyl synthase
Acetyl carboxylase
3-Hydroxy dehydratase
Acetyl transacylase
-Ketoacyl reductase
(b.). Briefly describe how fatty
acid synthesis is regulated by
AMP-dependent protein kinase
(AMPK).
AMPK is activated by AMP. AMPK phosphorylates and inactivates acetyl
carboxylase, the first enzyme in fatty acid synthesis, thereby inhibiting fatty acid
synthesis.
Name_____________KEY__________________
Student No._________________________________
EXTRA CREDIT POINTs (15 pts.)
TRUE/FALSE. Write “T” if the statement is true and “F” if the statement is false.
__T___ 1) Lipids derived from cholesterol aid digestion and absorption of other lipids such as
triacylglycerols.
__T___ 2) Vitamins A, E and K are all isoprenoids.
__F___ 3) Transport of ions and small molecules through a bacterial membrane pore requires energy from an
ATP to ADP conversion.
__T___ 4) The principle advantage of a cascade mechanism in signal transduction is that one molecule of a
ligand can affect many intracellular proteins without crossing the plasma membrane.
__T___ 5) A biotin-dependent enzyme is responsible for catalyzing the carboxylation of acetyl CoA.
__F___ 6) In mammals the oxidation of fatty acids produces a two-carbon product and the synthesis of fatty
acids begins with a two-carbon substrate.
__T___ 7) During starvation ketone bodies can take the place of glucose as a fuel for brain cells.
__T___ 8) Snake venom can cause the lysis of red blood cells due to the presence of phospholipase A2.
__T___ 9) Most of the free energy needed to drive ATP formation in the mitochondria is the result of an
electrical contribution from a charge gradient across the inner mitochondrial membrane.
__T___ 10) Complex II participates in both the electron transport chain and the citric acid cycle.
__T___ 11) Mitochondrial electron transport and ATP formation are interdependent.
__F___ 12) The light reactions of photosynthesis form carbohydrates from ATP, NADPH, H+ and CO2.
__T___ 13) Rubisco often makes up to 50% of the soluble protein in plant leaves.
__F___ 14) Most plants contain a rubisco enzyme that catalyzes only a carboxylation reaction in the fixation of
carbon dioxide.
__F___ 15) The CAM pathway and the Calvin cycle generally occur simultaneously in plants during the
daytime.