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Medical Biochemistry and Molecular Basis of Medical Genetics
Examination 7
October 16, 2006
1. Which of the following statements is TRUE of de novo pyrimidine synthesis but not of
de novo purine synthesis?
a. The base is synthesized onto a ribose-5-phosphate.
b. One-carbon fragments are donated by folic acid derivatives.
c. Carbamoyl phosphate donates an amide group.
d. An entire glycine molecule is incorporated into a precursor of the base.
2. Which of the following statements about bilirubin is TRUE?
a. It is made more soluble in the liver by attachment of residues of glucose.
b. It is produced by the degradation of heme.
c. It is excreted mainly in the urine.
d. It contains iron in the Fe2+ state.
3. Which of the following statements about nitrogen metabolism is NOT correct?
a. Glutamate is produced by the addition of ammonia to α-ketoglutarate via
glutamate dehydrogenase or by transamination.
b. Histidine is degraded to glutamate then to α-ketoglutarate.
c. Alanine can be formed from lactate by alanine transaminase.
d. Vitamin B12 transfers a methyl group from tetrahydrofolate to homocysteine.
4. Fibrinolysis serves to
a. turn off clot formation.
b. amplify the antithrombic effects of thrombin.
c. prevent clot formation at areas of the vascular endothelium that are not damaged.
d. all of the above.
5. A patient has begun excreting larger than normal amounts of uric acid in her urine. The
most likely source of the increased uric acid is an increased degradation of
a. AMP and CMP
b. GMP and TMP
c. AMP and GMP
d. AMP, GMP and TMP
6. Cells salvage free purine bases because
a. these bases can’t leave the cell.
b. these bases are toxic to the cell.
c. they are high energy phosphate molecules.
d. it takes less ATP to salvage these bases than to synthesize these bases de novo.
7. Which of the following cannot be synthesized by a patient with phenylketonuria?
a. dopamine
b. norepinephrine
c. epinephrine
d. All can be synthesized by this patient.
8. A 25 year old male patient wishes to take amino acid supplements in hopes of boosting
his muscle mass and providing more energy for his muscles. Which of the following
amino acid supplements would be most beneficial for him?
a. homocysteine
b. branched chain amino acids
c. glutamine and arginine
d. tyrosine
9. Which of the following amino acids is a starting material for the biosynthesis of heme,
creatine and purines?
a. glycine
b. glutamate
c. cysteine
d. alanine
10. In what way(s) are the disorders alcaptonuria and tyrosinemia I alike?
a. Homogentisate is an intermediate in the degradation of tyrosine.
b. Tyrosine is produced from phenylalanine.
c. The final steps of tyrosine degradation to fumarate and acetoacetate are blocked.
d. All the above explain why these disorders are alike.
11. A person has classical phenylketonuria. For this person,
a. phenylalanine can be replaced by tyrosine in the diet.
b. phenylalanine and tyrosine are both essential amino acids.
c. tyrosine is an essential amino acid, but phenylalanine is not.
d. phenylalanine is an essential amino acid, but tyrosine is not.
12. Protein degradation is usually increased during hypercatabolic states because
a. there is a negative nitrogen balance.
b. there is a positive nitrogen balance.
c. this provides amino acids that can be used as fuel.
d. cells take up less amino acids.
13. A newborn child is eliminating valine in his urine. This suggests the child
a. has acaptonuria.
b. has a deficiency in the α-ketoacid dehydrogenase needed to metabolize valine.
c. cannot metabolize leucine and isoleucine.
d. All of the above.
14. You and your study partner are having an argument. This time the issue is a patient’s
blood urea nitrogen (BUN) level following an overnight fast. After an overnight fast, a
patient went to the doctor’s office to have a fasting blood test. Most of the parameters
(HDL, VLDL, heme iron, etc) came back normal, but you both noticed the BUN level
was slightly elevated. Your partner says there is something wrong with this patient and
more tests should be ordered. You say the elevated BUN level is normal for a patient
who has been fasting overnight and there is nothing to worry about. Why are you
correct?
a. Increased metabolism of amino acids during an overnight fast results in
significant waste nitrogen, which enters the urea cycle.
b. Glutamine is an amino acid which can shuttle excess nitrogen from one tissue to
another.
c. The Cori cycle functions to bring nitrogen from the liver to peripheral tissues
without increasing the NH4+ level in the blood.
d. During an overnight fast, kidneys excrete excess ammonia directly into the urine
at the expense of urea, resulting in increased BUN.
15. The most common precursor of glutamine that is released from tissues/organs is
a. α-ketoglutarate.
b. glutamate.
c. aspartate.
d. phosphorylglutamine.
16. In the blood coagulation cascade, two activators common to many steps are
a. protein C and protein S
b. thrombin and fibrinogen
c. calcium and phospholipids
d. high molecular weight kininogen and kalikrein
17. A 65 year old woman has sub-optimal liver detoxification activity, leading to greaterthan-normal production of reactive oxygen species (ROS). You wish to help her boost
her detoxification pathways by dietary means, so you advise her to
a. increase her intake of riboflavin, niacin, folic acid, pyridoxine and Vitamin B12.
b. increase her intake of antioxidant nutrients.
c. decrease her exposure to toxins wherever possible.
d. all of the above.
18. You have a patient with mitochondrial dysfunction, and you suspect she may suffer
mitochondrial membrane damage from reactive oxygen species. The vitamins most
effective for protecting your patient’s mitochondrial membrane lipids would be
a. vitamin E and β-carotene
b. vitamin B12 and vitamin B6
c. vitamin B3 and vitamin E
d. vitamin C and Vitamin E
19. Which of the following cannot cross the blood brain barrier?
a. valine
b. glutamine
c. NH3
d. NH4+
20. Which of the following amino acids is NOT synthesized using 3-phosphoglycerate as a
starting material?
a. glycine
b. glutamate
c. serine
d. cysteine
21. The term “glucogenic amino acid” refers to amino acids that are
a. degraded to yield pyruvate or TCA cycle intermediates.
b. formed from glucose.
c. degraded to yield acetyl CoA or acetoacetate.
d. byproducts of the gluconeogenic pathway.
22. The role of the second phase of the detoxification pathway is to
a. conjugate polar molecules to the bioactivated toxin molecule.
b. bioactivate toxin molecules and increase their polarity.
c. reduce free radicals formed during the first phase of detoxification.
d. convert toxin molecules to intermediates of metabolic pathways when possible.
23. The source(s) of reactive oxygen species produced during the detoxification process is
(are)
a. conjugation enzymes
b. dehydrogenase enzymes
c. cytochrome P450 enzymes
d. all of the above.
24. Which of the following cannot be synthesized by a transamination reaction?
a. asparagine
b. glutamine
c. alanine
d. lysine
25. Which is the correct order regarding adhesion of platelets to damaged endothelial cells?
a. Thrombin binds to activated platelets, which promotes platelet binding to
subendothelial collagen, followed by release the granule contents and clot
formation.
b. GPIa binds subendothelial collagen, GPIb binds vWF, dimerized GPIIa-GPIIb are
exposed and form a fibrinogen binding site.
c. GPIa binds the endothelial cell plasma membrane, GPIb binds VWF, dimerized
GPIIa-GPIIb are exposed and form a fibrinogen binding site.
d. Activated platelets aggregate near the site of endothelial damage, GPIa binds
subendothelial collagen, GPIb binds vWF, dimerized GPIIa-GPIIb are exposed
and form a fibrinogen binding site.
26. A patient cannot absorb dietary niacin. To offset this deficiency she should increase her
intake of
a. tyrosine.
b. tryptophan.
c. thiamine.
d. thymine.
27. A patient with chronic reactive oxygen species (ROS) production within their
mitochondria might be expected to have deficiencies in their energy production pathways
due to
a. ROS- mediated damage to mitochondrial DNA.
b. the destruction of vitamins or minerals needed for the pathways.
c. deficiencies in glycolysis-mediated pyruvate production.
d. deficiencies in creatine-phosphate utilization by muscle.
28. Which of the following enzymes converts superoxide to hydrogen peroxide?
a. glutathione reductase
b. glutathione peroxidase
c. catalase
d. superoxide dismutase
29. In order to synthesize pyrimidines de novo, the cell requires
a. phosphoribosyl pyrophosphate (PRPP) for the initial step.
b. tetrahydrofolate for the incorporation of carbons 2 and 8.
c. aspartate to contribute carbon and nitrogen atoms to form the ring.
d. NH4+ as a substrate for carbamoyl phosphate synthetase II.
30. You and your study partner are trying to determine whether the microsomal ethanol
oxidizing system (MEOS) can be considered a detoxification pathway. Which of the
following properties of MEOS would make you think this?
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.