Download Biochemistry II, Test One

ANSWERS for Biochemistry II, Test One
(March 22, 2001)
Indicate whether each of the following statements about ATP is true of false.
(a) It contains a -N-glycosidic linkage. T
(b) It contains a furanose ring.
T
(c) It is the highest-energy compound in cells.
F
(d) It is used as a long-term storage form of energy in cells. F
(e) Its free energy of hydrolysis can be used to drive other reactions.
T
(f) It is synthesized from ADP and Pi in an exergonic reaction. F
(g) It contains three phosphoanhydride bonds.
F
(h) Repulsion between the negatively charged phosphoryl groups is reduced
when ATP is hydrolyzed.
T
(i) Its sugar moiety is glucose. F
(j) Its phosphoryl group transfer potential is higher than that of
phosphoenolpyruvate.
F
+
2. NAD : Answer: B
A. accepts 2 electrons and 2 hydrogen ions.
B. accepts 2 electrons and 1 hydrogen ion.
C. accepts 1 electron and 1 hydrogen ion.
D. transfers electrons in reductive biosynthesis.
E. in its oxidized form in NADH.
3. Consider the general reaction A B, where Go` = -60kJ/mol. Initially, 10
mM of A and 0 mM of B are present. After 24 hours, analysis reveals the
presence of 2 mM of B and 8 mM of A. What can you conclude from this
result? Answer: D
A. A and B have reached equilibrium concentrations.
B. Formation of B is thermodynamically unfavorable.
C. The result described is impossible, given the of the reaction.
D. Formation of B is kinetically slow; equilibrium has not been reached at
24
hours.
E. An enzyme has shifted the equilibrium toward formation of A.
4. Which statement is NOT true of phosphofructokinase-1? Answer: A
A. It is inhibited by fructose-2,6-bisphosphate.
B. It is activated by AMP.
C. It is inhibited by citrate.
D. It is inhibited by ATP.
E. ATP increases its K0.5 for fructose 6-phosphate.
5. All of the following statements describe glycolysis EXCEPT: Answer: B
A. It produces a net of 2 ATP molecules for each molecule of glucose.
B. Its rate is mainly regulated by hexokinase.
C. The glycolytic enzymes are found in the cytosol.
D. Two molecules of glyceraldehydes 3-phosphate are produced for each
glucose
molecule.
E. Its overall rate is regulated by the energy level of the cell.
Answers for Biochemistry II, Test Two (April 2, 2001)
(100 points total; 20 points for each question.)
Name:
; Student Number:
3. In order to examine the citric acid cycle you have obtained a pure
preparation of isolated, intact mitochondria. You add some succinyl-CoA to
the suspension of mitochondria. How many moles of ATP would you expect to
be generated in one turn of the citric acid cycle from each mole of
succinyl-CoA added to the test tube? Answer:
E (succinyl-CoA can not
enter the intact mitochondrion)
(a) 3
(b) 4
(c) 5
(d) 5.5
(e) No ATP would form under these conditions.
4. All of the following enzymes are linked to the reduction of NADH except:
Answer: C
A. Isocitrate dehydrogenase.
B. Lactate dehydrogenase.
C. Succinate dehydrogenase.
D. Pyruvate dehydrogenase.
E. -ketoglutarate drhydrogenase.
3. Indicate whether each of the following statements about the glyoxylate cycle is
true (T) or false (F).
F. It allows the products of fatty acid oxidation to be converted, eventually,
to
glucose. T
G. It provides intermediates for the citric acid cycle during periods when
amino acids are being synthesized. T
H. It depletes cellular stores of oxaloacetate. F
I. It occurs instead of the citric acid cycle in plants. F
4. Place the following steps in lipid oxidation in their proper sequence. (Note: this
is not a complete list of steps.) Answer: D, E, B, F, C,A
F. Thiolysis.
G. Reaction of fatty acyl-CoA with carnitine.
H. Oxidation requiring NAD+.
I. Hydrolysis of triacylglycerol by lipase.
J. Activation of fatty acid by joining to CoA.
K. Hydration.
5. How does the production of ketone bodies allow continued oxidation of fatty
acids? How does this affect the cytosolic coenzyme A concentration? (please write
the answer on the back of this page) Answer: The generation of ketone bodies
(which contain no CoA moiety) from acetyl-CoA frees up mitochondrial
coenzyme A for continued fatty acid oxidation. The separation of the coenzyme A
pools of the cytosol and the mitochondrial matrix is maintained by the
acyl-carnitine/carnitine transport system. Ketone body production therefore
does not affect the cell’s cytosolic CoA concentration.
Biochemistry II, Test Three (April 16, 2001)
4. Which of the following is a characteristic of many aminotransferase reactions?
Answer: b
(b) They have a large, negative G`o.
(c) The amino group is transferred to an -keto acid (such as
-ketoglutarate) to form the corresponding amino acid.
(d) The amino group is transferred from an ammonia molecule.
(e) They are catalyzed by the same enzyme.
(f) They require the cofactor S-adenosylmethionine.
5. Early in its life, a tadpole lives in an aqueous environment and excretes much
of its excess nitrogen as ammonia. Once it matures into an adult, the frog
spends more time on dry land and becomes ureotelic. Which of the following
enzyme activities would be most likely to increase drastically in the adult
frog?
Answer:
A
A. Carbamoyl phosphate synthetase I.
B. Glutamine synthetase.
C. glutaminase.
D. carboxypeptidase.
E. -ketoglutarate dehydrogenase.
3. Indicate whether each of the following statements about the mitochondrial
electron transfer chain and oxidative phosphorylation is true (T) or false (F).
J. NADH dehydrogenase complex, cytochrome bc1 complex, and
cytochrome oxidase all are transmembrane proteins. T
K. Synthesized ATP must be transported into the intermembrane space
before it can enter the cytosol. T
C. Cytochrome c and the F1 part of ATPase are peripheral membrane
protein.
Answer:
T
C. Complexes I, II, III, and IV all are proton pumps. F
D. Ubiquinone is a hydrophilic molecule.
F
E. Ubiquinone and the Fo part of ATP synthase are both peripheral
membrane proteins.
F
F. The final electron acceptor is H2O. F
4.Which of the following statements about photosystem II is correct.
Answer:
C
L. It is located in the inner mitochondrial membrane.
M. It contains the electron carrier with the most negative E`o in the entire
photosynthetic system..
N. It contains an Mn-containing complex that splits water.
O. Its final electron acceptor is NADP+.
P. H2O is the only electron donor capable of regenerating P680 from P680*..
Biochemistry II, Test Four (April 30, 2001)
5. Which of the following correctly matches the glycolytic reaction with the
gluconeogenic enzyme used in the corresponding bypass reaction?
Answer: a
(b) Glucose
glucose 6-phosphate; glucose 6-phosphatase.
(c) Fructose
6-phosphate
fructose
1,6-bisphosphate;
phosphofructokinase-2.
(d) Fructose 1,6-bisphosphate
dihydroxyacetone phosphate +
glyceraldehydes
3-phosphate;
glyceraldehyde
3-phosphate
dehydrogenase.
(e) 2-phosphoglycerate
phosphoenolpyruvate: phosphoglycerate kinase.
(f) Phosphoenolpyruvate
pyruvate; pyruvate kinase.
6. Carbon fixation involves a condensation reaction between CO2 and:
Answer: C
A. 3-phosphoglycerate.
B. Phosphoglycolate.
C. Ribulose 1,5-bisphosphate.
D. Fructose 6-phosphate.
E. Ribose 5-phosphate.
7. A sample of malonyl-CoA synthesized from radioactive (14C-labeled) HCO3and unlabeled acetyl-CoA is used in fatty acid synthesis. In which carbon(s)
will the final fatty acid be labeled? (Recall that the carboxyl carbon of the
fatty acid is C-1)
Answer:
E
L. Every carbon.
M. Every odd-numbered carbon.
C. Every even-numbered carbon.
G. Only the carbon farthest from C-1.
H. No part of the molecule will be labeled.
4.Which of the following statements about cholesterol synthesis is not true?
Answer:
E
Q. Reduction of HMG-CoA to mevalonate catalyzed by HMG-CoA
reductase is the committed step.
R. Acetyl-CoA is the ultimate source of all 27 carbon atoms of cholesterol.
S. It is inhibited by elevated levels of intracellular cholesterol.
T. It is hormonally inactivated by glucagons and activated by insulin.
U. It occurs in the mitochondrial matrix.
Biochemistry II, Test Five (May 28, 2001)
8. Which of the following is not true of nitrogen fixation by the nitrogenase
complex? Answer: c
(a) This enzyme complex is inactivated by exposure to oxygen.
(b) ATP binding causes a change in the conformation of the reductase
moiety.
(c) The primary role of ATP is to drive nitrogen fixation through the
hydrolysis of PPi.
(d) Nitrogen fixation occurs only in prokaryotes.
(e) The final electron acceptor in this process in N2.
9. In nucleotide metabolism, all of the following are true except: Answer: D
A. The committed step in purine biosynthesis is the transfer of an amino
group to PRPP.
B. Both purine and pyrimidine biosynthesis are regulated by
end-product inhibition.
C. Nucleotide can be synthesized in a single reaction via salvage
pathways.
D. De novo pyrimidine synthesis begins with a molecule of PRPP.
E. Orotidylate is the common precursor in the biosynthesis of
pyrimidines, and inosinate is the common precursor in the
biosynthesis of the purines ATP and GTP.
10. In the laboratory, some E. coli cells have been grown with transcription
inhibitors so that only replication could occur. You break open the cells;
gently purify the DNA, separating it from the rest of the cell contents; then
treat the intact DNA with radioactively-labeled antibodies to DNA ligase and
DNA polymerase I. Where do you expect to find the highest concentration of
these enzyme antibodies? Answer:
D
N. On the leading strand, in one direction from the point of origin.
B. On the leading strand, in both directions from the point of origin.
I. On the lagging strand, in one direction from the point of origin.
J. On the lagging strand, in both directions from the point of origin.
K. On all parts of the DNA molecule equally.
4. Both homologous recombination and transposon-type recombination: Answer:
D
V. Occur between homologous regions on chromosomes.
W. Are important in the repair of damaged DNA.
X. Involve RecA protein.
Y. Generate genetic diversity.
Z. The two types of recombination have nothing in common.
考试课程
Biochemistry II
1. If the G` of the reaction A
2001
年
6 月 11 日
B is –12 kJ/mol, which of the
following statements are correct? (Note the prime symbol means that a
thermodynamic parameter is measured at pH.7.0) (2 points)
A.
B.
C.
D.
The reaction will proceed spontaneously from left to right at the given conditions.
The reaction will proceed spontaneously from right to left at standard conditions.
The equilibrium constant favors the formation of B over the formation of A.
The equilibrium constant could be calculated if the initial concentrations of A and B
were known.
E. The value of G`o is also negative.
Answer(s): A, D
2. Which of the following statements about ATP and its roles in cells are true? (2 points)
A. The ATP molecule is kinetically unstable and is thus consumed within about one
minute following its formation in cells.
B. ATP provides free energy to a thermodynamically unfavorable reactions by group
transfer, always donating a Pi to form a covalent intermediate.
C. ATP can be regenerated by coupling with a reaction that releases more free energy
than does ATP hydrolysis.
D. A transmembrane proton-motive force can drive ATP synthesis.
E. The active form of ATP is usually in a complex with Mg2+.
Answer(s): C, D, E
3. A common moiety for NADP, NAD, FMN, FAD, and coenzyme A is: (2 points)
A. A pyrimidine ring;
B. A three ring structure;
C. An ADP;
D. A pyranose ring;
E. A triphosphate group.
Answer(s): C
4. If the C-1 carbon of glucose were labeled with 14C, which of the carbon atoms in pyruvate
would be labeled after glycolysis? (2 points)
A. The carboxylate carbon;
B. The carbonyl carbon;
C. The methyl carbon.
Answer(s): C
5. Which of the following are metabolic products of pyruvate in higher organisms? (2 points)
A. Glycerol
B. Lactic acid
C. Acetone
D. Acetyl-CoA
E. Ethanol
Answer(s): B, D
6. Indicate whether each of the following statements about the pentose phosphate pathway is
true (T) or false (F). (5 points)
A. It generates NADH for reductive biosyntheses. F
B. The reactions occur in the cytosol. T
C. Transketolase and transaldolase link this pathway to gluconeogenesis. F
D. It is more active in muscle cells than in fat-storage cells. F
E. It interconverts trioses, tetroses, pentoses, hexoses, and heptoses. T
7. Which of the following statements are correct? The citric acid cycle (2 points)
A. does not exist as such in plants and bacteria, because its functions are performed
by the glyoxylate cycle.
B. oxidizes acetyl CoA derived from fatty acid degradation.
C. produces most of the CO2 in anaerobic organisms.
D. provides succinyl CoA for the synthesis of carbohydrates.
E. provides precursors for the synthesis of glutamic and aspartic acids.
Answer(s): B, E
8. Match the cofactors of the pyruvate dehydrogenase complex with their corresponding
enzyme components and with their roles in the enzymatic steps that are listed. (5 points)
A. Coenzyme A: 3,7
B. NAD+: 2, 9
C. Thiamine pyrophosphate (TPP): 1, 5
D. FAD: 2, 6
E. Lipoamide: 3, 4,8
(1). Pyruvate dehydrogenase component
(2). Dihydrolipoyl dehydrogenase
(3). Dihydrolipoyl transacetylase
(4). Oxidizes the hydroxylethyl group
(5). Decarboxylates pyruvate
(6). Oxidizes dihydrolipoamide
(7). Accepts the acetyl group from acetyllipoamide
(8). Provides a long, flexible arm that coveys intermediates to different enzyme component.
(9). Oxidizes FADH2.
9. Matching the role in fatty acid oxidation and/or mobilization to the appropriate
component listed below. (5 points)
A. Bile salt: 2
B. Serum albumin:5
C. ApoC-II:4
D. Apolipoprotein:3
E. Carnitine:1
(1). Acts as a “carrier” of fatty acids across the inner mitochondrial membrane.
(2). Acts as a biological detergent, disrupting fat globules into small mixed micelles.
(3). Binds and transports triacylglycerols, phospholipids, and cholesterol between organs.
(4). Activates lipoprotein lipase, which cleaves triacylglycerols into their components.
(5). Binds some fatty acids molibized from adipocytes and transports them in the blood to
heart and skeletal muscle.
10. Which of the following answers complete the sentence correctly? Surplus dietary amino
acids may be converted into (2 points)
A. proteins.
B. Fats.
C. ketone bodies.
D. glucose.
E. a variety of biomolecules for which they are precursors.
Answer(s): A, B, C, D,E
11. Which of the following compounds serves as an acceptor for the amino groups of many
amino acids during metabolism? (2 points)
A. Glutamine
B. Asparagine.
C. -ketoglutarate.
D. Oxaloacetate
E. Glutamate
Answer(s):C
12. Match the functions for the coenzymes that are involved in amino acid metabolism. (4
points)
A. Pyridoxal phosphate: (3)
B. Coenzyme B12: (2)
C. Tetrahydrobiopterin: (1)
D. NAD+: (1)
E. Biotin (4)
(1). Carries electrons
(2). Provides free radicals
(3). Carries amino groups
(4). Carries CO2.
13. Which of the following experimental observations would not support the chemiosmotic
model of oxidative phosphorylation? (3 points)
A. If mitochondrial membranes are ruptured, oxidative phosphorylation cannot
occur.
B. Raising the pH of the fluid in the intermembrane space results in ATP synthesis in
the matrix.
C. Transfer of electrons through the respiratory chain results in formation of a
proton gradient across the inner mitochondrial membrane.
D. The orientation of the enzyme complexes of the electron transfer chain results in a
unidirectional flow of H+.
E. Radioactively labeled inorganic phosphate is incorporated into cytosolic ATP only
in the presence of an H+ gradient across the inner mitochondrial membrane.
Answer(s): B
14. Some photosynthetic prokaryotes use H2S, hydrogen sulfide, instead of water as their
photosynthetic hydrogen donor. How does this change the ultimate products of
photosynthesis? (2 points)
A. Carbohydrate (CH2O) is not produced.
B. H2O is not produced.
C. Oxygen is not produced.
D. ATP is not produced.
E. The products do not change.
Answer(s): C
15. Which of the following are constituents of chlorophylls? (2 points)
A. Substituted tetrapyrrole.
B. Plastoquinone.
C. Mg2+.
D. Fe2+.
E. Phytol.
F. Iron porphyrin.
Answer(s): A, C, E
16. The observation that the incubation of photosynthetic algae with 14CO2 in the light for a
very brief time (5s) led to the formation of 14C-labeled 3-phosphoglycerate suggested that the
14CO was condensing with some two-carbon acceptor. That acceptor was in fact which of
2
the following? (2 points)
A. Acetate
B. Acetyl CoA
C. Acetyl phosphate
D. Acetaldehdyde
E. Glycerol phosphate
F. None of the above
Answer(s): F
17. Which of the following are common features of the syntheses of mevalonate (an
intermediate of cholesterol biosynthesis) and ketone bodies? (2 points)
A. Both involve 3-hydroxyl-3-methylglutaryl CoA (HMG-CoA).
B. Both require NADPH.
C. Both require the HMG-CoA cleavage enzyme.
D. Both occur in the mitochondria.
E. Both occur in liver cells.
Answer(s): A
18. S-adenosylmethionine is involved directly in which of the following reactions. (3 points)
A. Methyl transfer to phosphatidyl ethanolamine.
B. Synthesis of glycine from serine.
C. Synthesis of polyamines.
D. Conversion of homocysteine to methionine.
E. Generation of the 5` cap of the eukaryotic mRNAs.
Answer(s): A, C, E
19.Which of the following does not provide a carbon skeleton for the synthesis of amino
acids? (2 points)
A. succinate.
B. -ketoglutarate
C. Pyruvate.
D. Oxaloacetate.
E. Ribose-5-phosphate.
Answer(s): A
20. Which of the following compounds directly provide atoms to form the purine ring? (3
points)
A. Aspartate.
B. Carbamoyl phosphate.
C. Glutamine.
D. Glycine.
E. CO2.
F. N5,N10-methylenetetrahydrofolate.
G. N10-formyltetrahydrofolate.
H. NH4+.
Answer(s): A, C, D, E, G
21. Which of the following statements about ribonucleotide reductase are true? (2 points)
A. It converts ribonucleoside diphosphates into 2`-deoxyribonucleoside diphosphates
in humans.
B. It contains coenzyme B12, which generates free radicals needed for the catalysis.
C. It accepts electrons directly from FADH2.
D. It receives electrons directly from either thioredoxin or glutaredoxin.
E. It contains two kinds of allosteric regulatory sites: one for controlling the overall
activity and the other for controlling the substrate specificity.
Answer(s): A, D, E
22. Biosynthetic pathways that require NADPH include which of the following? (2 points)
A. Gluconeogenesis.
B. Fatty acid biosynthesis.
C. Ketone body formation.
D. Cholesterol biosynthesis.
E. Tyrosine biosynthesis.
Answer(s): B,D,E
23. Homologous recombination in E. coli is likely to require which of the following? (3
points)
A. DnaB protein.
B. RecA protein.
C. RecBCD complex.
D. ATP.
E. NAD+.
F. Single-strand DNA binding protein.
G. DNA-dependent RNA polymerase.
H. DNA polymerase I.
I. DNA ligase.
J. dATP.
Answer(s): B, C, D, E, F, H, I, J
24. Which of the following statements about E. coli promoters are correct? (2 points)
A. They may exhibit different transcription efficiencies.
B. For most genes they include variants of consensus sequences.
C. They specify the start sites for transcription on the DNA template.
D. They have identical and defining sequences.
E. They are activated when C or G residues are substituted into their –10 regions by
mutation.
F. Those that have sequences that correspond closely to the consensus sequences and
are separated by 17 base pairs are very efficient.
Answer(s): A, B, C, F
25. The AAUAAA sequence on a RNA molecule marks (2 points)
A. The site where ribosomes bind to initiate polypeptide synthesis.
B. The site where transcription stops.
C. The site near which the primary transcript is cleaved and a poly (A) sequence is
added.
D. The site where the release factor will bind to end polypeptide synthesis.
E. The site where polyribonucleotide phosphorylase will add a stretch of random
sequences.
Answer(s): C
26. The 70 subunit of the E. coli RNA polymerase: (2 points)
A. acts as the catalytic site for polymerization.
B. Recognize promoters.
C. Has a proofreading function.
D. Increases the processivity of the enzyme.
E. Recognizes termination signals.
Answer(s): B
27. The discontinuity of eukaryotic genes were first revealed by: (2 points)
A. Using footprinting techniques.
B. DNA sequence comparison.
C. RNA sequence analysis.
D. Electron microscopic analysis of RNA-DNA hybrid molecules.
E. Plant genetic studies.
Answer(s): D
28. Which of the following mRNA codons can be recognized by the tRNA anticodon ICG. (2
points)
A. UGC.
B. CGA.
C. UGA.
D. CGU.
E. CGC.
Answer(s): B, D, E
29. A new compound, vivekine, was recently discovered by a clever undergraduate student.
It was isolated from bacteria found in deep sea-dwelling organisms. Vivekine inhibits protein
synthesis in eukaryotes: Protein synthesis can initiate, but only dipeptides are formed and
these remain bound to the ribosome. This toxin affects eukaryotic protein synthesis by
blocking the: (2 points)
A. binding of formylmethionyl-tRNA to ribosomes.
B. activity of elongation factors.
C. activation of amino acids.
D. recognition of stop signals.
E. formation of peptide bonds.
Answer(s): B
30. Indicate whether each of the following statements about prokaryotic
translation is true (T) or false (F). (7 points)
A. An aminoacyl-tRNA synthetase catalyzes formation of an ester bond. ( T )
B. An mRNA molecule cannot be used to direct protein synthesis until it has been
completely transcribed. ( F )
C. The positioning of fMet-tRNA on the A site defines the reading frame. ( F )
D. Incoming aminoacyl-tRNA are first bound to the A site. ( T )
E. Formation of the 70S initiation complex requires an input of energy. ( T )
F. The carboxyl group of the amino acid on the aminoacyl-tRNA is transferred to the
amino group of a peptidyl-tRNA.( F )
G. Release factors cause the peptidyl transferase activity of the ribosome to use H2O as
a substrate. ( T )