-Biochemistry Questions-

Questions 1-5

1. A 38 year old man has an MI.  Within two years, he has a stroke.  His previous history is significant for 4 bone fractures, and not finishing high school because it was 'too hard'.  What would you most expect to find?

A. Branched chain amino acids in the urine

B. phenylketones in the urine

C. cysteine in the urine

D. cystathione synthase deficiency

E. vitamin B1 deficiency

2. What finding would you most expect to see in a patient with increased glucocerebroside?

A. atypical macrophages

B. cherry-red spot on macula

C. gargoylism

D. premature atherosclerosis

3. A man has a defect in the production of collagen that results in a Berry aneurysm.  Which type of collagen is most likely affected?

A. I

B. II

C. III

D. IV

E. V

4. A defect in carbamoyl phosphate synthase I is most likely to result in:

A. heart damage

B. liver damage

C. kidney damage

D. brain damage

5. Prolonged use of broad-spectrum antibiotics would most likely result in what vitamin deficiency?

A. vitamin A

B. vitamin K

C. vitamin E

D. vitamin D

Answers 1-5

1. Answer D  This man has homocystinuria, which is caused by a deficiency in cystathionine synthase, or homocysteine methyltransferase.  It causes early MI's and strokes, as well as mental retardation.  Here's a study song to help <http://www.youtube.com/watch?v=MGCaW_woXUI&feature=channel_page>.

2. Answer A  A deficiency in the enzyme beta-glucocerebrosidase causes elevated glucocerebroside in Gaucher's disaease.  It is the most common lysosomal storage disease.  A key feature is Gaucher's cells, which are wrinkly macrophages. 

3. Answer C  Type III collagen is the most likely to be found in blood vessels.  Type I is mostly bone, and type IV is basement membrane.

4. Answer D  Carbamoyl phosphate synthase I is the rate limiting enzyme in the urea cycle.  NH₄⁺

would build up, and the CNS is the most affected.  Most defects in amino acid metabolism result in brain injury

5. Answer B  Vitamin K is synthesized by intestinal bacteria.

Questions 6-10

6.  Which amino acid is used in both purine and pyrimidine synthesis?

A. His

B. Val

C. Asp

D. Gly

E. Glu

7. The proofreading capability of DNA Polymerase III comes from

A. 3'→5' exonuclease activity

B. 5'→3' exonuclease activity

C. 5'→3' ligase activity

D. topoisomerase activity

E. only DNA Polymerase I has proofreading capability

Answers 6-10

6. Answer C  Purines use Glu, Gly, and Asp.  Pyrimidines use Asp.

7. Answer A  DNA Polymerase III is the main polymerase.  It proofreads by going in reverse from 3'→5'.   DNA Polymerase I is what degrades the RNA primer.  5'→3' exonuclease activity is shared by both DNA Pol I and III.