Download 1 - VCOMcc

Medical Biochemistry and Molecular Basis of Medical Genetics
Examination 4
November 5, 2007
1. Carbamoyl phosphate synthetase I (CPS I) produces carbamoyl phosphate using what
source of nitrogen?
a. glutamine
b. NH4+
c. glutamate
d. alanine
2. Which of the following shows the single carbon groups arranged from most oxidized
(left) to most reduced (right)?
a. methyl, methylene, methenyl, formate
b. formate, methylene, methyl, methenyl
c. methylene, methenyl, formate, methyl
d. formate, methenyl, methylene, methyl
3. When a platelet cell comes in contact with a site of vascular endothelial cell damage,
a. it binds to the exposed subendothelial layer.
b. it releases thrombin first to start the activation sequence.
c. it lyses and releases a number of factors.
d. it shrinks to fit into the site of damage.
4. Which of the following pair of molecules is commonly interchanged by a transamination
reaction?
a. lactate and alanine
b. α-ketoglutarate and glutamate
c. glutamate and glutamine
d. all of the above
5. For Hartnup’s disease neutral amino acids such as phenylalanine cannot be imported into
intestinal epithelial cells. However, dipeptides that contain phenylalanine can be
imported normally. This suggests that patients with Hartup’s disease
a. have intestinal epithelial cells that lack amino acid transporters and therefore
cannot take up individual amino acids.
b. can still obtain phenylalanine from dietary sources.
c. can’t make tyrosine from phenylalanine.
d. must get phenylalanine from tyrosine degradation.
6. A medical student gets a bad headache while studying biochemistry and he takes aspirin
to relieve the pain. What effect will this have on his body’s ability to synthesize
prostaglandins? (Assume the aspirin affects 100% of its target protein(s))
a. Only arachadonic acid liberated by diacylglycerol lipase can be used.
b. Only arachadonic acid liberated by monoacylglycerol lipase can be used.
c. Only arachadonic acid liberated by phospholipase A2 can be used.
d. None of the above statements are true.
7. Which of the following amino acids is considered strictly ketogenic?
a. isoleucine
b. leucine
c. valine
d. glutamate
8. What is the source of the methyl group that vitamin B12 uses to convert homocysteine to
methionine?
a. methyl tetrahydrofolate
b. methylene tetrahydrofolate
c. cysteine
d. homocystine
9. The difference between a soft fibrin clot and a hard fibrin clot is
a. soft clots have more water embedded in the clot.
b. hard clots are formed on the extracellular matrix.
c. hard clots have extensive cross-linked fibrin.
d. soft clots have extensive cross-linked fibrin.
10. During purine and pyrimidine degradation, what is usually salvaged?
a. the free bases
b. PRPP
c. inosine
d. uracil
11. Ethanol can be converted to acetaldehyde by alcohol dehydrogenase (ADH) or by the
MEOS. Which of the following describes the difference in the reaction carried out by
these two systems?
a. ADH is in the cytoplasm whereas MEOS is in the mitochondria.
b. ADH is in the mitochondria whereas MEOS is in the cytoplasm.
c. ADH produces one NADH during this step whereas MEOS consumes one
NADPH during this step
d. ADH consumes one NADH during this step whereas MEOS produces one
NADPH during this step.
12. Classical phenylketonuria is caused by a deficiency of ___________ , whereas malignant
phenylketonuria is caused by a deficiency of ____________.
a. cystathionase, cystathionine synthase
b. dihydropteridine reductase, phenylalanine hydroxylase
c. phenylalanine hydroxylase, dihydropteridine reductase
d. phenylalanine in the diet, phenylalanine metabolism
13. The role of the second phase of the detoxification pathway is to
a. reduce free radicals formed during the first phase of detoxification.
b. convert toxin molecules to intermediates of metabolic pathways when possible.
c. conjugate polar molecules to the bioactivated toxin molecule.
d. bioactivate toxin molecules and increase their polarity.
14. A person consumes a large plate of French fries (fat and starch). Which of the following
enzymes most likely will NOT be active?
a. acetyl CoA carboxylase
b. HMG CoA reductase
c. lipoprotein lipase
d. pancreatic lipase
15. What two purine bases are synthesized using IMP as a starting material?
a. AMP and UMP
b. CMP and GMP
c. AMP and GMP
d. CMP and TMP
16. Methotrexate inhibits
a. dihydropteridine reductase
b. thymidylate synthase
c. phenylalanine hydroxylase
d. dihydrofolate reductase
17. Conjugated bilirubin that ends up in urine most likely comes from _________, whereas
conjugated bilirubin that ends up in the stool most likely comes from __________.
a. blood, bile
b. lymph, bile
c. blood, pancreas
d. bile, blood
18. Brain uses glutamine as a precursor for the synthesis of neurotransmitters. For this
purpose, brain cells import
a. glutamate.
b. ammonia.
c. branched chain amino acids.
d. branched chain amino acids and ammonia.
19. Which of the following amino acids is NOT synthesized from an intermediate of
glycolysis or the TCA cycle?
a. serine
b. aspartate
c. leucine
d. glutamate
20. Fibrinolysis is the process of
a. clot formation via thrombin.
b. converting fibrinogen to fibrin.
c. degrading fibrin clots.
d. activating C-protein.
21. Ethanol metabolism can interfere with fatty acid oxidation and glycolysis because
a. ATP from ethanol metabolism down regulates these other catabolic pathways.
b. ethanol metabolism increases the cellular NADH level.
c. NADH from ethanol metabolism blocks the malate-asparte shuttle system.
d. all of the above.
22. Adipose cells build new triglycerides for storage using which of the following
metabolites?
a. glycerol 3-phosphate
b. glycerol
c. pyruvate
d. all of the above
23. Gout is most likely caused by inadequate excretion of what pyrimidine breakdown
product?
a. hypoxanthine
b. xanthine
c. uric acid
d. inosine
24. A three year old child exhibits signs that her enzymes δ-ALA dehydratase and
ferrochelatase are inhibited. What does this suggest?
a. lead poisoning
b. iron deficiency
c. hemosiderin deficiency
d. insufficient bilirubin conjugation
25. A patient has a deficiency in bile salt re-adsorption in the gut. Because of this deficiency,
the patient most likely will
a. have increased cholesterol synthesis in her liver cells.
b. not be able to digest dietary fat.
c. exhibit steatorrhea (fatty stools).
d. be unable to form chylomicrons.
26. How is the microsomal ethanol oxidizing system (MEOS) similar to a detoxification
pathway?
a. It is a cytochrome P450 mixed oxidase
b. It is induced by high levels of ethanol
c. It can produce free radicals.
d. All of the above.
27. Which of the following stimulate(s) the urea cycle?
a. insulin.
b. glucagon.
c. insulin and cortisol.
d. epinephrine and cortisol.
28. The redox cofactor required for fatty acid synthesis is
a. NADH.
b. NADPH.
c. NAD+.
d. NADP+.
29. One primary difference between consuming a meal containing carbohydrates and protein
versus a protein-only meal is
a. insulin increases the absorption of amino acids by intestinal epithelial cells.
b. the presence of glucagon increases the absorption of amino acids by muscle cells.
c. intestinal epithelial cells can use amino acids for energy.
d. in the presence of insulin, ingested amino acids will be used for protein synthesis.
30. Proper red blood cell production by hematopoesis requires tetrahydrofolate (FH4) because
a. FH4 is required to produce dTMP for DNA synthesis in these cells.
b. FH4 is required to produce dUMP for RNA synthesis in these cells.
c. Vitamin B12 must pick up methyl groups from FH4 for neuronal development.
d. 5-fluoruracil can inhibit thymidylate synthase.
31. When HDL particles pick up cholesterol from cellular membranes, it most likely will be
a. transferred to VLDLs and chylomicrons.
b. esterified to increase its hydrophobicity.
c. carried to other cells to be transferred to its cellular membranes.
d. none of the above are true.
32. During the hypercatabolic state, a patient is in a negative nitrogen balance because
a. the kidneys eliminate glutamine rapidly since they can’t process the nitrogen they
are receiving.
b. proteins are being degraded to provide amino acids for energy, leading to excess
nitrogen that is eliminated.
c. dietary amino acids are becoming incorporated into proteins that are newly
synthesized.
d. their body is not gaining nitrogen as fast as they would under normal metabolic
conditions.
33. Homogentisate accumulation in a patient suggests the patient may have
a. alcaptonuria.
b. an error in tyrosine metabolism.
c. a defect in homogentisate oxidase.
d. all of the above.
JEM Note: this was included to make up for the problems on Exam1…
BONUS Questions 34-37 refer to the cell cycle figure on the right. In the figure, the letters
correspond to distinct phases of the cell cycle. For each statement below, select the letter
corresponding to the most appropriate cell cycle phase. Letter choices may be used more than
once, if necessary.
34. Phase where cells divide.
35. The DNA replication phase.
D
B
36. The final growth phase prior to mitosis.
37. After a temporary resting period, liver cells
re-enter the cell cycle at this phase when they
have been stimulated to divide.
A
C
G0
38. The conversion of nascent chylomicrons to mature chylomicrons requires
a. ApoE.
b. ApoB48.
c. ApoCII.
d. HDL.
39. A bright medical student wanted to develop a way to increases a person’s blood HDL
level. He figured he would manufacture capsules containing predominantly HDL
particles that a person could ingest, resulting in higher blood HDL levels. Assuming he
could produce such a capsule, would the ingested HDL particles make it into a person’s
blood stream?
a. Yes: these complex particles are difficult for the body to make, so the digestive
system will absorb them intact.
b. Yes: these particles will be broken down into constituent parts first, absorbed,
then reassembled for delivery to the lymph system then the blood.
c. No: intestinal cells don’t contain receptors for HDL particles, so the cells won’t
recognize that the particles are present in the gut.
d. No: digestive enzymes in the gut will break the particles down to constituent parts
which will be absorbed by the intestinal cells and passed to the lymph / blood.
40. Following a 24 hour fast, a patient consumes a carbohydrate meal. Within an hour after
the meal,
a. the patient’s hormone sensitive lipase is inactive.
b. the patient’s lipoprotein lipase is inactive.
c. the patient’s fatty acid synthesis pathway is inactive.
d. all the above statements are true.
41. A patient with classical phenylketonuria will be able to synthesize L-dopamine provided
they have a dietary source of
a. tetrahydrofolate.
b. tetrahydrobiopterin.
c. L-tyrosine.
d. L-tryptophan.
42. Humans can’t synthesize the essential amino acids. Which of the following essential
amino acids can humans degrade? (Assume no disease states or deficiencies).
a. isoleucine
b. tryptophan
c. histidine
d. humans can degrade all amino acids
43. Type III hyperlipidemia is caused by a deficiency of apoprotein E. Analysis of the blood
of patients with this disorder would most likely exhibit
a. above normal levels of VLDL after eating.
b. normal triglyceride levels.
c. above normal triglyceride levels.
d. below normal triglyceride levels.
44. A patient has an extremely low blood LDL level. How would this most likely affect the
LDL receptors in his cells?
a. His receptors would have higher than normal affinity for LDL.
b. His receptors would have lower than normal affinity for LDL.
c. His cells would produce elevated levels of LDL receptors.
d. His cells would stop producing LDL receptors.
45. Along with Ca2+ ions, phospholipids can activate many factors in the blood coagulation
cascade. Where are the phospholipids that activate these factors?
a. blood lipoproteins
b. the subendothelial layer
c. the platelet cell membrane
d. in the liver
46. A patient is receiving drug therapy to decrease cholesterol synthesis in her cells. The
drug binds to the HMG-CoA reductase. Which of the following would most likely NOT
occur as a result of this drug therapy?
a. Her cells would increase production of LDL receptors.
b. Her cells would decrease synthesis of fatty acids.
c. Her blood level of LDL would be lower than before the drug therapy.
d. SREBP activation of the Sterol Response Element would be increased in her cells.
47. When amino acids are absorbed by intestinal epithelial cells they
a. are immediately deaminated and exported to the blood.
b. are used exclusively by these cells to meet their amino acid requirements.
c. pass into the blood then enter cellular pools to be used for a variety of purposes.
d. mostly enter the cell by a simple diffusion mechanism.
48. Most tissues export glutamine as a way to eliminate excess nitrogen, whereas the kidney
actively takes up glutamine. Kidney uses glutamine
a. as a nitrogen source for the urea cycle.
b. as a nitrogen source for regulating urine pH.
c. in a transamination pair for aspartate.
d. as a nitrogen source to synthesize neurotransmitters for export to the brain.
49. Human desaturase enzymes can place double bonds in fatty acids only at carbons
between the carbonyl carbon and
a. carbon 10.
b. carbon 9.
c. carbon 8.
d. the ω carbon.
50. A patient has an Apoprotein E (ApoE) deficiency. Compared to patients without an
ApoE deficiency, this patient most likely will have
a. more VLDL / IDL remnants in his blood.
b. less chylomicron remnants in his blood.
c. more chylomicron and VLDL / IDL remnants in his blood.
d. more chylomicron remnants but less VLDL / IDL remnants in his blood.
51. The lipoprotein lipase that has the highest affinity for VLDL triglyceride is found in
a. muscle.
b. adipose.
c. liver.
d. all tissues have a lipoprotein lipase enzyme with equivalent affinity.
52. The difference between 2-monoacylglycerol and lysophospholipid is
a. they are both produced by a lipase-type enzyme.
b. one is a triglyceride and one is a glycerophospholipid.
c. one is produced from a triglyceride and the other from a glycerophospholipid.
d. they are powerful detergent-like molecules that aid in the ingestion of fat.
53. Which of the following would most likely be in the greatest abundance in the blood
during a time of fasting?
a. chylomicrons
b. VLDLs
c. LDLs
d. HDLs
54. Intermediate density lipoproteins (IDLs) are often formed from
a. HDLs that have given off their protein constituents.
b. HDLs that have picked up significant amounts of cholesterol.
c. VLDLs that have more triglyceride than normal.
d. VLDLs that have depleted levels of triglyceride.
55. Which cofactor is required for the transamination reactions of amino acid synthesis and
degradation?
a. PLP
b. NADH
c. thioredoxin
d. tetrahydrofolate
56. Which of the following is NOT a typical use for cholesterol?
a. component of cell plasma membranes.
b. precursor for bile salts.
c. precursor for glycerophospholipid headgroups.
d. precursor for steroid hormones.
57. Which of the following is NOT an enzyme involved in digestion of proteins?
a. pepsin
b. amylase
c. carboxypeptidase
d. amino peptidase
58. Muscle eliminates excess nitrogen by exporting which of the following molecules?
a. NH4+
b. alanine
c. glutamine
d. alanine and glutamine
59. Glucagon signaling results in the activation of many cellular proteins, which changes the
metabolic state of the cell. Which of the following enzymes most likely would be
activated due to glucagon signaling?
a. pyruvate kinase
b. glycogen synthase
c. pyruvate dehydrogenase
d. protein kinase A
Questions 60-63 refer to the diagram below. Choose the letter that corresponds to molecule that
best fits the description.
60. Formed by a lipoxygenase enzyme.
61. Formed from PGH2.
62. Most common starting material for eicosanoid synthesis in humans.
63. Immediate precursor for thromboxane synthesis.
64. The fate(s) of newly synthesized fatty acids / triglycerides in the liver is (are)
a. incorporation into VLDLs for export to the blood.
b. export to adipose tissue via VLDL.
c. export to muscle via VLDL to be used as energy.
d. all the above.
65. Maple syrup urine disease is caused by a defect in
a. branched chain amino acid absorption.
b. transamination of the branched chain amino acids in cells.
c. oxidative decarboxylation of branched chain α-keto acids during branched chain
amino acid degradation.
d. conversion of malonyl CoA to propionyl CoA during branched chain amino acid
degradation.
66. Which phospholipase enzyme can remove IP3 from the phospholipid PIP2?
a. phospholipase A1
b. phospholipase A2
c. phospholipase C
d. phospholipase D
67. Creatine phosphate helps maintain a high energy charge in muscle cells by
a. donating inorganic phosphate to ADP to regenerate ATP.
b. producing ADP that can be used by the ATP synthase to make more ATP.
c. promoting creatinine excretion to keep creatine levels normal.
d. none of the above.
68. Body organs exchange amino acids and their metabolites in order to
a. provide a source of energy for the different tissues.
b. provide a means to safely move waste nitrogen around the body.
c. provide starting material for protein synthesis and the synthesis of nitrogencontaining compounds.
d. all of the above.
69. What is the most likely mechanism by which ethanol enters liver cells?
a. ethanol transporter
b. passive diffusion
c. aquaporin
d. MEOS
70. During the fed state, when the insulin to glucagon ratio is high, ATP levels are generally
low because
a. most cells are using glucose as an energy source rather than fatty acids.
b. NAD+ and NADP+ levels are also low.
c. a large amount of ATP is being used for anabolic pathways.
d. catabolic pathways are shut down so ATP is not produced.
71. Proteinase enzymes used in digestion are
a. synthesized as inactive precursors.
b. activated in the digestive tract.
c. degraded as they progress through the digestive system.
d. all the above.
72. A newborn infant with a potentially fatal hyperammonemia (excess ammonia in the
blood) was found to have no N-acetylgluatamate synthase activity in the liver, and so this
infant could not produce N-acetylgluatamate (NAG). Direct administration of NAG
restored the ammonia blood level to normal levels. The enzyme stimulated by NAG was
a. carbamoyl phosphate synthetase I.
b. ornithine transcarbamoylase.
c. argininosuccinate synthetase.
d. arginase.
73. Which of the following does NOT regulate the activity of the acetyl CoA carboxylase
(ACC) enzyme?
a. insulin / glucagon ratio
b. cytoplasmic acetyl CoA
c. palmitoyl CoA
d. citrate
74. Which of the following contribute atoms for both purine and pyrimidine ring synthesis?
a. CO2 and acetyl CoA
b. glutamine and aspartate
c. glycine and 10-formyl-tetrahydrofolate
d. HCO3- and glutamine