Bio302 Biochemistry II,
Midterm Examination 1, March 27, 2002
Questions 1-10, each 5 points, Questions 11-18 each 10 points.
Answer only FIVE of the questions among 11-18.
Question 1.
Protein kinases
a) use Thr, Ser, or Tyr as the acceptor groups for phosphoryl transfer.
b) transfer the a (alqha) phosphorus atom of ATP.
c) are located on the external surface of cells.
d) transfer a phosphoryl group from one protein to another.
e) use AMP as substrate.
Question 2.
Protein kinase A
a) is activated by ATP
b) consists of two C (catalytic) and two R (regulatory) subunits in the absence of activator.
c) upon binding the activator dissociates into one C2 and two R subunits.
d) contains a pseudosubstrate sequence in the C subunits.
Question 3.
A. Describe the mechanism of activation for the zymogens below. Give also the names of their active forms and
where they are located:
a) Pepsinogen
b) Trypsinogen
c) Chymotrypsinogen
d) Proelastase
e) Procarboxypeptidase
B. How the active forms of the above zymogens are inactivated?
Question 4.
Which of the properties listed below are characteristics of a peripheral or an integral protein.
a) bind to the surface of membranes
b) have transmembrane domains
c) require detergents fo dissociation from the membrane
d) require mild salt or pH treatment for dissociation from the membrane
Question 5.
For the following structures below, write down
a) which are phosphoglycerides?
b) which is a glycolipid
c) which contain sphingosine?
d) which contain choline?
e) which contain glycerol
Question 6.
For a bacterium moving toward an increasing concentration of an attractant, which of the following statements are
correct?
a) tumbling will be more frequent
b) tumbling will be less frequent
c) The clockwise rotation of flagella will occur more frequently.
d) The counterclockwise rotation of flagella will occur more frequentlly.
Question 7.
The methyl-accepting chemotaxis proteins
a) may bind attractants or repellents directly
b) may interact with soluble, periplasmic chemosensors.
c) Are reversibly methylated in the periplasmic domain.
d) Are reversibly methylated in the cytosolic domain.
e) have common periplasmic domains in each of the four proteins in this family.
Question 8.
Which of the following are the second messengers that are produced by the phosphoinositide cascade?
a) Phosphatidyl inositol 4,5-bisphosphate.
b) Inositol 1,3,4-trisphosphate
c) Inositol 1,4,5-trisphosphate
d) Inositol 4-phosphate
e) Inositol 1,3,4,5-tetrakisphosphate
f) Diacylglycerol
Question 9.
True or false? Receptor tyrosine kinases
a) Are integral membrane enzymes.
b) Are often activated by ligand-induced dimerization
c) Can phosphorylate themselves on their cytoplasmic domains when activated by their ligands.
d) Are seven-helix transmembrane receptors.
e) Activate their targets via G proteins.
Question 10.
Why do membrane proteins not flip-flop across membranes?
Answer only the FIVE of the questions below. Each 10 points.
Question 11.
Describe how one could prepare a liposome for the purpose of transporting a water-soluble drug to specifically
targetted to a particular type of cells.
Question 12.
Distinguish between channels and pumps with respect to selectivity, energy requirement and speed. List the forms
of energy that can drive active transport.
Question 13.
Explain the ion selectivity of the acetylcholine receptor channel. Compare Na+, K+ and ClQuestion 14.
Draw a Schiff base. (Show an attaching group (show as R) is Schiff based to an amino acid side chain on a
protein.)
Question 15.
Describe the role of sodium-calcium exchanger. Compare its capacity to transport Ca2+ with the Ca2+-ATPase.
Question 16.
Describe how restoration of the dark state is achieved, following the light induced changes in retinal cell. (outline
the enzymatic cascade for adaptation to light)
Question 17.
What evidences might implicate that cAMP is a second messenger?
Question 18.
Define oncogene and relate oncogene function to G proteins. Give an example.
Bio302 Biochemistry II
Midterm Examination I , March 28th, 2003
Answer 8 of the questions among questions 1-9 (each 5 points).
Answer 6 of the questions amogn question 10-16 (each 10 points).
Question 1. Fill in the blanks:
a)…………………………is a technique to measure conductance across a membrane.
b) Passages between contiguous cells are called… …………………
c) Molecules that can pass through membranes are … ……………………….
d) Membrane transporters that couple downhill flow of one species against the uphill flow of another
species
are called… …………………….
e) A channel that open in response to membrane depolarization are called… …………….
Question 2. Fill in the blanks:
a) Organisms that use energy of sunlight and convert it to chemical energy are called……………...
b) In aerobic respiration the ultimate acceptor of electrons is………………….
c) ……………………….is a carrier of two carbon acyl groups.
d) NADH is an electron carrier derived from the vitamin…………………...
e) Reaction pathways that require energy, often biosynthetic processes are called………………….
Question 3. The free energy change for hydrolysis of ATP to ADP is
a) - 2.2 kcal/mol.
b) - 33 kcal/mol.
c) –7.3 kcal/mol.
d) –14.6 kcal/mol.
e) 7.6 kcal/mol.
Question 4. Fats are a more efficient energy source than carbohydrates because they are more
A) oxidized. B) polarized. C) reduced. D) All of them. E) None of them.
Question 5. The reduced form of flavin adenine dinucleotide is
a) FADH.
b) FAD.
c) FADH++
d) FADH2.
E) none of them.
Question 6. How does the potassium channel maintain selectivity for potassium vs. sodium ions?
a) The ion size is the determining factor.
b) The size of the ion and associated waters relative to the pore size is the determining factor in channel
selectivity
c) Dehydration of the potassium ion is compansated energetically by interactions with oxygen atoms in the filter,
which is not possible with sodium ions.
d) All of the above
e) None of the above
Question 7. What is the function of the sarcoplasmic reticulum Ca+2 ATPase?
a)
b) to maintain a calcium ion concentration of 90 mM in the cytosol and 1.5 mM in the SR.
c)
SR.
d) to maintain an equivalent concentration during heavy cellular metabolic activity
e) none of the above.
Question 8. How can a molecule undergo both passive transport and facilitated diffusion simultaneously?
Question 9. What is the purpose of using toxins such as bungarotoxin or cobratoxin in membrane studies?
OBS! Answer only 6 of the questions below!
Question 10. How can site-directed mutagenesis be used to determine the mechanisms of ion channels?
Question 11. What is the advantage of having several different, but almost identical, subunits as opposed to
having multiple copies of the same subunit?
Question 12. An extract of Digitalis purpurea plant is used to treat heart failure. How does it function?
Question 13. How is metabolism controlled? If many compounds are common to both anabolic and catabolic
paths, how can metabolism be controlled? Explain.
Question 14. During cyclic-AMP mediated hormone activation, what are the three steps at which amplification
occurs?
Question 15. What secondary messenger molecules are produced by the phosphoinositide cascade? What are their
major target enzymes?
Question 16. Explain how a Ca+2 ionophore could mimic the effects of a hormone?
Bio 302 Biochemistry II
Midterm Examination I, March 31st, 2004
Questions 1-10 each 5 points, questions 11-15 each 10 points.
Question 1. Match the four cofactors in the left column with the appropriate structural features and properties
from the right column.
a) ATP
1) nicotinamide ring
b) FAD
2) adenine group
c) NAD+
3) isoalloxazine ring
d) CoA
4) acyl group transfer
5) electron transfer
6) phosphate transfer
Question 2. Which of the following statements about G proteins are correct?
a) G proteins are activated by twelve-membrane receptors only
b) G proteins make up a large family of proteins that are involved in regulating enzymes, chemotaxis, visual
excitation, and ion channels.
c) G proteins cycle between a GTP form and an GDP form by means of a self-catalyzed exchange reaction.
d) Activated seven-helix proteins switch them on by causing the exchange of GTP for GDP.
e) Certain G protein can participate in a reaction with NAD+ that leads to their covalent modification, for
example, reactions catalyzed by cholera and pertussis toxins.
Question 3. Which of the following are the second messengers that are produced by the phosphoinositide
cascade?
a) Diacylglyerol (DAG).
b) Inositol 4-phosphate.
c) Inositol 1,3,4,5-tetrakisphosphate.
d) Phosphatidyl inositol 4,5-bisphosphate (PIP2).
f) Inositol 1,4,5-trisphosphate (IP3)
Question 4. Which of the following statements about cyclicAMP are correct?
a) ATP is converted to cyclicAMP by the enzyme adenylate cyclase in one step.
b) Cyclic AMP is converted to 5’-AMP by a phosphodiesterase-catalayzed reaction with H2O.
c) Cyclic AMP binds the catalytic subunits of protein kinase A and activates the enzyme allosterically.
d) Cyclic AMP interacts with a hormone-receptor complexş to dissociate the hormone.
e) The hormone receptor complex enters the cell and affects the activities of target enzymes.
Question 5. Which of the following answer complete the sentence correctly?
The reactions catalyzed by phosphofructokinase and by pyruvate kinase are similar in that
a) both involve a "high-energy" sugar derivative
b) both are essentially irreversible
c) both generate ATP
d) both involve three-carbon compounds
e) neither of the above
Question 6. When blood glucose levels are low, glucagon is secreted. Which of the following are the effects of
increased glucaogon levels on glycolysis and related reactions in liver?
a) Phosphofructokinase is activated.
b) Phosphofructokinase in inhibited.
c) Fructose bisphospatase 2 is activated.
d) Fructose bisphosphatase 2 is inhibited.
e) Glycolysis is accelerated.
f) Glycolysis is slowed down.
Question 7. Which of the following answer complete the sentence correctly?
The reactions catalyzed by phosphofructokinase and by pyruvate kinase are similar in that
a) both involve a "high-energy" sugar derivative
b) both are essentially irreversible
c) both generate ATP
d) both involve three-carbon compounds
e) neither of the above
Question 8. Lactase deficiency is characterized by the inability to hydrolize
a) -1,4 glucosidic bonds.
b) -1,6 glucosidic bonds.
c) -1,4 glucosidic bonds.
d) -1,6 glucosidic bonds.
e) -1,4 galactosidic bonds.
Question 9. Which of the following statements about glucose transporters are true?
a) They are transmembrane proteins
b) They accomplish the movement of glucose across animal cell plasma membranes
c) Their tissue distribution and concentration can depend on the tissue type and metabolic state of the
organism
d) They constitute a protein family of five isoforms.
Question 10. State whether true or false.
a) Receptor tyrosine kinases activate their targets via the G protein cascade.
b) Receptor tyrosine kinases can phosphorylate themselves on their cytoplasmic domains when activated.
c) Receptor tyrosine kinases that have been activated by hormone binding are recognized by target proteins
having SH2 (scr protein homology region 2) sequences.
d) Some oncogenes encode tyrosine kinases.
e) Epidermal growth factor (EGF) is a protein kinase that phosphorylates tyrosine residues.
o
Question 11.
’=–7.3 kcal/mol.
rolysis of ATP to ADP +Pi is approximately –12 kcal/mol. Use this
information to calculate the approximate ratio of [ATP] to [ADP][Pi] found in cells at 37oC. (Gas constant,R=
1.987 cal/mol.oK)
Question 12.
An uncharged molecule is transported from side 1 to side 2 of a membrane. It’s concentration is 10-1 M on side 1
and 10-4 M on side 2. Will the transport be an active or a passive process? Explain your answer.
(Gas constant,R= 1.987 cal/mol.oK)
Question 13.
The potassium channel is over 100 times more permeable to potassium than to sodium. Explain the molecular
mechanism for this selectivity.
Question 14.
Explain how the action of a single hormone molecule can be “amplified”. Give an example.
Question 15.
Explain how calmodulin serves as a calcium sensor in most eukaryotic cells.
Bio302 Biochemistry II
Midterm Examination I, March 31st, 2005
Answer all the questions from 1-8 (each 5 points)
But answer only 6 of the 7 questions among questions 9-15 (each 10 points)
Question 1 (5 points) Which of the following are the second messengers that are produced by the
phosphoinositide cascade?
a) Phosphatidyl inositol 4,5-bisphosphate
b) Inositol 1,3,4-trisphosphate
c) Inositol 1,4,5-trisphosphate
d) Inositol 4-phosphaıte
e) Inositol 1,3,4,5-tetraksphosphate
f) Diacylglycerol
Question 2. (5 points) True or false? Receptor tyrosine kinases
a) integral membrane enzymes.
b) are often activated by ligand-induced dimerization
c) can phosphorylate themselves on their cytoplasmic domains when activated by their ligands
d) are seven-helix transmembrane receptors.
e) activate their targets via G proteins.
Question 3. (5 points) Which of the following enzymes have impaired activity in vitamin B1 deficiency?
a) succinate dehydrogenase
b) pyruvate dehydrogenase
c) isocitrate dehydrogenase
d) a-ketoglutarate dehydrogenase
e) dihydrolipoyl trasacetylase
Question 4. (5 points) Conversion of citrate to isocitrate is a type of ............. reaction.
a) oxidation
b) isomerization
c) condensation
d) ligation
e) none of the above
Question 5. (5 points) Beri-beri is caused by a deficiency of.................................
a) riboflavin
b) pantothenic acid
c) thiamine
d) all of the above
e) none of the above
Question 6. (5 points) Metabolite required to convert 3-phosphoglycerate to 2-phosphoglycerate is
a) 1-phophogycerate
b) diacylglycerol
c) NADH
d) 2,3-bisphosphogycerate
e) 1,3-bisphospogycerate
Question 7. (5 points). What is the structural feature common to ATP, FAD, NAD+ and coenzymeA?
Question 8. (5 points). Since lactate is a “dead-end” product of metabolism in the sense that its sole fate is to be
re-converted into pyruvate, what is the purpose of its formation?
OBS! Chose 6 of the 7 questions below!!!!!!
Question 9. (10 points) What evidences might implicate that cAMP is a second messenger?
Question 10. (10 points) Explain how the action of a single hormone molecule can be “amplified”. Give an
example.
Question 11. (10 points) Explain how calmodulin serves as a calcium sensor in most eukaryotic cells. Describe
how calmodulin activates target proteins. Give an example.
Question 12. (10 points) What is the effect of increasing the concentration of each of the following metabolites on
the net rate of glycolysis. Briefly explain each answer.
a) glucose 6-phosphate:
b) fructose 1,6-bisphosphate:
c) fructose 2,6-bisphosphate:
d) citrate
Question 13. (10 points) What are the two metabolic products formed from pyruvate in yeast which turns grape
juice into champagne? Name the two enzymes involved in this reaction.
Question 14. (10 points) What is the purpose of hexokinase variants in different mammalian cells? Liver has a
variant of hexokinase, known also as glucokinase (or hexokinase IV) a monomeric protein which shows sigmoidal
kinetics in contrast to other hexokinases which obey Michaelis-Menten kinetics. Explain the purpose of this
variation.
Question 15
poximately -12
kcal/mol (standard free energy change for this reaction is
o
’= -7.3 kcal/mol). Calculate the expected ratio of [ATP] to [ADP+Pi] found in cells at 37oC. (Gas constant
R= 1.987 cal.M-1K-1, K=oC+273.15)
Bio301, Biochemistry II, Midterm Examination 1, March 26, 2007
Fill in the blanks:
1. The specific transport of a species down its concentration gradient is referred to as_...............................
2. Membrane pums are energy ……………………………..
3. In ……………………………………………. a phosphoryl group is transferred from ATP to a specific
aspartate residue.
4. Cardiac steroids such as digitoxigenin inhibit the………………………………
5. The lactose permease transports lactose into the cell along with a …………………………
6. The acetylcholine receptor is an example of a……………………………-gated channel.
7. ………………………………………………… is a primary messenger that is released by the adrenal gland.
8.………………………………… is another name for the seven-transmembrane helix receptors.
9. The
d to the cell membrane by being covalently
linked to this molecule (……………………………………….).
10. This enzyme (…………………………….) becomes active when bound to Ca2+ and diacylglycerol.
11. This protein (…………………………………….) binds to calcium ions and serves as a Ca2+ sensor in
eukaryotic cells.
12………………………………………………..is a secondary messenger and is abbreviated IP3
13…………………………………………is the membrane protein that catalyzes the conversion of ATP to camp
14. The cytosolic side, or β subunit, of the insulin receptor is a ……………………………kinase.
15. The binding of IP3 to the IP3 receptor results in the release of ……………………………from the endoplasmic
reticulum.
16………………………………………………… binds to β-andrenergic receptors
17. The Acetyl group is attached to Coenzyme A by a ……………………………………….bond.
18…………………………… reactions form new bonds by using free energy from ATP cleavage.
19. Activated carriers……………………..and…................................... and…………………. contain adenosine
diphosphate units.
20. G proteins are converted from the GTP bound form to the GDP bound form by nucleotide……………………
they are converted from the GDP bound form to the GTP bound form by………………………………… .
21. How does the potassium channel maintain selectivity for potassium versus sodium
ions?
A) The ion size is the determining factor.
B) The size of the ion and associated waters relative to the pore size is the
determining factor in channel selectivity.
C) Dehydration of the potassium ion is compensated energetically by interactions
with oxygen atoms in the selectivity filter, which is not possible with sodium ions.
D) All of the above.
E) None of the above.
22. When a molecule moves from a concentration of 10 M to 10 M, is the process
spontaneous, at equilibrium, or does it require an input of energy?
A) at equilibrium
D) All of the above.
B) input of energy required
E) None of the above.
C) spontaneous
23. What are the two messenger products formed by cleavage of PIP2?
A) diacylglyercol and inositol 1,4,5-triphosphate
B) diacylglyercol and inositol 1,3,5-triphosphate
C) diacylglyercol and inositol 1,3-diphosphate
D) diacylglyercol phosphate and inositol 1,4,5-trisphosphate
E) None of the above.
24 How is calmodulin activated?
A) by binding of both calcium and potassium
B) by binding Ca2+ when the cytosolic concentration is greater than 500 nM
C) by binding to a positively charged helix on another protein
D) All of the above.
E) None of the above.
25 How does the potassium channel maintain selectivity for potassium versus sodium ions?
A) The ion size is the determining factor.
B) The size of the ion and associated waters relative to the pore size is the
determining factor in channel selectivity.
C) Dehydration of the potassium ion is compensated energetically by interactions
with oxygen atoms in the selectivity filter, which is not possible with sodium ions.
D) All of the above.
E) None of the above.
26. (10 points) Define action potential, and explain its mechanism in terms of the transient changes in Na and K
permeability of the plasma membrane of a neuron.
27. (15 points) Show (by calculation!) that the hydrolysis of a single ATP molecule provide sufficient energy for
the process of transporting 3 molecules of Na+ out and two molecules of K+ into the cell under cellular conditions
in which Na+ is present 143 mM outside and 14 mM inside the cell, and K+ is present 4 mM outside and 157
mM inside the cell at a membrane potential is -60 mV (inside negative) at 37oC.
(Faraday constant is 23.1 kcal.V-1mol-1, and Gas constant is 1.987 cal.mol-1.K-1)
Bio302 Biochemistry II
Second Midterm Examination, April 27, 2007
Multiple choice questions have one correct answer, each 4 points.
Question 1. (10 points) Fill in the blanks
a) The is another name for glycolysis:……………………..
b) This is the process by which noncarbohydrate precursor molecules are converted into
glucose:……………………..
c) This substance must be regenerated for glycolysis to proceed:………………….
d) This intermediate is necessary for the conversion of galactose to glucose:…………
e) This molecule is an allosteric inhibitor of phosphofructokinase:………………
f) This essential nutrient is required for the carboxylation of pyruvate in humans:
g) This is an allosteric activator of glycolysis:……………………..
h) The key enzyme that regulates the pace of glycolysis is……………………….
i) The common structural domain of NAD binding dehydrogenases is often called
a………………………………………..after the scientist who first recognized it.
j) In alcoholic fermentation, the decarboxylation of pyruvate requires a coenzyme that contains the
vitamin………………………
Question 2. What is the purpose of phosphorylating glucose in cytosol?
a) to trap glucose in the cell
b) to destabilize glucose and facilitate the next series of metabolic steps
c) to convert it to a more soluble form
d) all of the above
e) a and b
Question 3. What reaction is catalyzed by aldolase?
a) isomerization of DHAP to GAP
b) ligation of GAP and DHAP
c) reversible cleavage of F-1,6-BP to DHAP and GAP
d) cleavage of DHAP to GAP
e) irreversible aldol condensation of DHAP and GAP
Quastion 4. How are the glycolytic enzymes regulated?
a) transcriptional control
b) reversible phosphorylation
c) allosteric control
d) all of the above
e) none of the above
Question 5. (5 points) Why is it more sensible for phosphofructokinase to be an important control step rather than
hexokinase?
Question 6. (5 points) How are gluconeogenesis and glycolysis regulated reciprocally?
Question 7. (5 points) What is a substrate cycle. What two functions are attributed to substrate cycles?
Question 8. Which of the following vitamins are precursors to cofactors necessary for the formation of acetyl
CoA?
a) thiamine, riboflavin, niacin, lipoic acid, and pantothenic acid
b) thiamine, riboflavin, niacin, lipoic acid, pantothenic acid, and biotin
c) thiamine, ribobflavin, niacin, and biotin
d) thiamine, riboflavin, and lipoic acid
e) none of the above
Question 9. Formation of citrate is a(n) ……………………………..reaction.
a) oxidation
b) reduction
c) condensation
d) ligation
e) hydrolysis
Question 10. (5 points) Fill in the blanks
a) The location of succinate dhydrogenase is………………………
b) This substance is toxic, because it reacts qith the neighboring sulfhydry groups of dihydrolipoyl groups and
blocks its reoxidation to lipoamide:…………………..
c) This is the name applied to metabolic reactions that replenish citric acid cycle intermediates that are
depleted because they were used for biosynthesis:………………..
d) These proteins are tightly associated with FAD or FMN:……………..
e) This is the site at which citric acid reactions takes place.:………………………..
Question 11. Which of the following functions as a “flexible swinging arm* when it transfers the reaction
intermediate from one active site to the next?
a) FAD
b) NAD+
c) Lipoamide
d) Thiamine pyrophosphate
e) Coenzyme
Question 12. Which of the following conditions will activate pyruvate dehydrogenase kinase which catalyzes the
phosphorylation and inactivation of E1 in the pyruvate dehydrogenase complex?
a) elevated concentrations of NADTH and ATP
b) elevated concentrations of NAD+ and ADP
c) Ca++
d) Insulin
e) Elevated concentrations of acetyl-CoA
Question 13. (5 points) Explain why a GTP is energetically equivalent to an ATP in metabolism.
Question 14. (5 points) What is the energy source that drives the condensation of oxaloacetate and acetylCoA to
produce citrate by citrate synthase? Explain.
Question 15. (5 points) Fill in the blanks.
a) This electron carrier is a derivative of quinone and has an isoprenoid tail:………………….
b) This enzyme catalyzes the reduction of oxygen:………………….
c) A strong oxidizing agent has a strong tendency to…………………..(accept/donate) electron(s).
d) The transfer of a single electron to O2 forms the reactive………………………ion.
e) Cytocrome…………….is the only water soluble cytochrome of the electron transport chain.
Question 16. In prokaryotes the site of ATP synthesizing machinery is
a) the mitochondrial matrix
b) the outer cell wall
c) the cytoplasmic membrane
d) the nucleolus
e) none of the above
Question 17. Which of the following does not pump protons?
a) Complex I
b) Complex II
c) Complex III
d) Complex IV
e) All o the above
Question 18. In the Rieske center, the iron sulfur center is coordinated to the amino acids
a) His
b) Cys
c) His and Cys
d) Cys and Met
e) None of them
Question 19. (5 points) Explain why less ATP is made from the reoxidation of FADH2 as compared to NADH.
Question 20. (5 points) What is the actual function of the protons in the synthesis of ATP by FoF1 ATP synthase?
Question 21. How is light used in photosynthesis?
a) The light is necessary to make the chlorophyll green, so the pigment can transmit electrons.
b) The light is used to generate high energy electrons with great reducing potential
c) The light provides heat energy for the chloroplasts.
d) The light is absorbed by oxygen which is converted into water
e) None of the above
Question 22. (5 points)Why are chlorophylls good candidates or photoreceptors?
BIO302 Biochemistry II
Final Examination, June 6, 2003
Question
a) The major energy storage compound of animals is fats (except in muscles). Why would this be advantageous?
b) Why don’t plants use fats/oils as their major energy storage compound?
Answer: for mobile organisms weight can be a critical actor, and packing the most energy into the least weight is
decidedly advantageous. B) for immobile plants, weight is not a critical factor, and it costs more energy to make
fat/oil than starch.
Question
In fatty acid synthesis malonyl-CoA is used as a “condensing group” rather than acetyl-CoA. Suggest a reson for
this.
Answer: Energy is needed to condense an acetyl group to the growing fatty acid. In theory, such could be done
with acetyl;CoA, using ATP. In practice, the ATP is used to convert acetyl-CoA to malonyl-CoA, the
condensation of the acetyl moiety of malonyl-CoA is driven in part of the accompanying decarboxylation and
requires no additional energy. Another possible reason is to avoid a metabolic confusing of pathways particularly
in uncompartmented prokaryotes. Malonyl-CoA says “synthesis”, acetyl-CoA says “degradation”.
Question
Match hexokinase and glucokinase with the descriptions from the right column that are appropriate
a) hexokinase
1) is found in the liver
b) glucokinase
2) requires ATP for reaction
3) is specific for glucose
4) has a broad specificity for hexoses
5) has a high KM value for glucose
6) is inhibited by glucose 6-phosphate
b) glucokinase shows sigmoidal kinetics in contrast to other hexoses which obeys Michaelis-Menten kinetics. Is
this an advantage?
Answer:
1 a, b, 2 a, b, 3 b, 4 a, 5 b, 6 a
Question
Which of the following conversions take place in a metabolic situation that requires much more NADPH than
ribose 5-phosphate, as well as complete oxidation of glucose 6-phosphate to CO2?
a) glucose 6-phosphate  ribulose 5-phosphate
b) ribose 5-phosphate  fructose 6-phosphate  glyceraldehyde 3-phosphate
c) fructose 6-phosphate  glucose 6-phosphate
d) fructose 6-phosphate  glyceraldehyde 3-phosphate  ribose 5-phosphate
e) glyceraldehyde 3-phosphate  pyruvate
Answer: a, b, c
Question
Liver synthesizes fatty acids and lipids for export to other tissues. Would you expect the pentose phosphate
pathway to have a low or a high activity in this organ.? Explain your answer.
Answer: NADPH is required for reductive biosynthesis. Therefore pentose phosphate pathway is high in the liver.
Question
Which of the following statements about the hormonal regulation of glycogen synthesis and degradation are
correct?
a) Insulin increases the capacity of the liver to synthesize glycogen.
b) Insulin is secreted in response to low levels of bood glucose.
c) Glucagon and epinephrine have opposing effects on glycogen metabolism.
d) Glucagon stimulates the breakdown of glycogen, particularly in the liver.
e) The effects of all three of the regulating hormones are mediated by cyclic AMP.
Answer: a, d
Wnite down the open chemical formula for oleic acid (C18:1 cis- 9).
Answer: CH3(CH2)7CH=CH(CH2)7CO2H
Explain thermogenesis. (How heat is generated to maintain body temperature).
Bio302 Biochemistry II
Final Examination June 4, 2004
Question 1. (10 points)
Compare ATP, NADH and NADPH with respect to their functions in metabolism.
Question 2. (20 points)
A (10 points) Name the seven-transmembrane helix proteins that you know. Can you make any suggestions for
relations between these proteins? What are the common features for this group?
B (10 points). Some oncogenes are variants of G-proteins (like v-ras). Describe what could make a regulatory Gprotein an oncogene.
Question 3. (5 points)
Fill in the blanks:
Phosphofructokinase is the most important control enzyme in glycolytic pathway of mammals. It is stimulated by
............................................which .........................its affinity for fructose 6-phosphate. One other regulator of
phosphofructokinase is ................................................ . Increasing concentration of
......................................................... inhibits phosphofructokinase.
Question 4. (5 points)
You are interested in studying citric acid cycle enzymes. You are given a calf liver as the starting tissue. Which
subcellular fractions would you separate to purify your enzymes?
a) cell membrane
b) nucleus
c) endoplasmic reticulum
d) mitochondria
e) cytoplasma
Question 5. (10 points).
Under anaerobic conditions gluconeogenesis is unlikely to occur. Why? Discuss briefly.
Question 6. (10 points)
A. (5 points)What are the two metabolic products formed from pyruvate in yeast which turns grape juice into
champagne?
B. (5 points) Name the two enzymes involved in this reaction.
Question 7. (10 points)
What is the purpose of hexokinase variants in different cells?
Liver has a variant of hexokinase, known also as glucokinase (or hexokinase IV), which shows sigmoidal kinetics
in contrast to other hexokinases which obey Michaelis-Menten kinetics. Explain the purpose of this variation.
In fact, glucokinase is a monomeric protein which shows cooperative behaviour. Suggest how this cooperativity
can be achieved.
Question 8 (10 points).
Why is the pentose phosphate pathway more active in cells that are dividing than in cells that are not?
Question 9 (10 points)
What is phosphorolysis? Explain briefly why it would be the preferred reaction in glycogen breakdown?
Question 10 (10 points)
Outline the effects of insulin on glycogen synthase . How does this effect achived?
Bio302 Biochemistry II
Final Examination, June 7, 2005
Please answer all the questions, each 10 points. Good luck!
Question 1: When O2 is aded to an anaerobic suspension of cells consuming glucose at a high rate, the rate of
glucose cosumption declines dramatically as the O2 is used up, and accumulation of lactate ceases. This effect
(called Pasteur effect) is characteristic of most cells capable of both aerobic ad unaerobic glucose catabolism.
Answer the questions below and relate to the action of the specific enzymes involved in this process.
a) Why does the presence of O2 decrease the rate of glucose consumption?
b) Why does the accumulation of lactate cease after O2 is added?
Question 2: Acetyl-CoA carboxylase is the principal regulation point in the biosynthesis of fatty acids. The
enzyme exists in two interconvertible forms that differ markedly in their activities: an inactive protomer to an
active filamentous polymer. Citrate and isocitrate bind to the filamentous form, and palmitoyl-CoA binds
preferentially to the protomer. Explain how this property is consistent with the regulatory role of acetyl-coA
carboxylase in the biosynthesis of fatty acids.
Question 3: Glycogen phosphorylase is the key enzyme in glycogen breakdown. The figure below shows different
forms of this enzyme.
A: Using the figure explain and discuss the two primary control mechanisms which acts to control tightly the
activity of this enzyme in muscle.
B: Which are the active forms of muscle phosphorylase? Which form requires high leves of AMP to be regulated?
Which convrsions antagonize by ATP ad glucose-6-phosphate?
Question 4: What are the similarities between fatty acid synthesis and degredation? Discuss. What are the
similarities of fatty acid synthesis and protein synthesis?
Question 5. How is pyrophosphate formation is important in chemistry? Give two examples.
Question 6: Explain the terms or processes given below:
a)Thermogenesis; b) Homolytic cleavage; c) Chemiosmotic hypothesis;
d)Fermentation;
e) Anaplerotic reactions;
Question 7: What ratio of NADPH to NADP+ is required to sustain [GST]= 10 mM and [GSSG]= 1 mM (reduced
gluthathione and oxidized gluthathione, respectively) at 25oC? (Use the redox potentials given in Table 1. At this
temperature RxT=1.36 kcal/mol).
Bio302 Biochemistry II.
Final Examination. May 30, 2007
Please answer only 10 of the questions below (each 10 points).
Question 1. How is pyrophosphate formation important in chemistry? Explain and give at least three
examples.
Question 2. What is the purpose of hexokinase variants in different cells?
Question 3. Describe how blood glucose level is regulated in the liver. (Describe the sequence of events in
muscle and in brain) which is responsible for glucose increase in blood.
Question 4. Individuals with thiamine deficiency display a number of characteristic neurological signs:
loss of reflexes, anxiety, and mental confusion. Why might thiamine deficiency be manifested by changes in brain
function?
Question 5. Describe respiratory control and relate it to energy charge.
Question 6. Explain thermogenesis.
Question 7. Why is the pentose phosphate pathway more active in cells that are dividing than in cells that
are not?
Question 8. Can animals convert fatty acids to glucose? How? Or Why not?
Question 9. Which reaction is catalyzed by RUBISCO? Describe the C4 pathway of RUBISCO and its
adaptive value to tropical plants
Question 10. What is gluthathione? Describe its function. Why it is important for blood cells?
Question 11. A sample of glycogen from a patient with liver disease is incubated with Pi (inorganic
phosphate), normal glycogen phosphorylase, and normal debranching enzyme. It was found that the ratio of
glucose-1-phosphate to glucose formed in this reaction mixture is 100. What is the patient’s most likely enzymatic
deficiency? What is the probable structure of the patient’s glycogen? Explain.
Question 12. Show (by drawing) a homolytic cleavage of a C-H bond. Name and describe the role of the
vitamin that play a role in homolytic cleavage.
Question 13.What are ketone bodies? Under what conditions they form?