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CASE FILES: BIOCHEMISTRY
C O M P R E H E N SIO N Q U E ST IO N S
[3.1]
A 44-year-old woman who recently lost her job because of absen-
teeism, presents to her physician complaining of loss of appetite,
fatigue, muscle weakness, and emotional depression. The physical
examination reveals a somewhat enlarged liver that feels firm and
nodular, and there is a hint of jaundice in the sclerae and a hint of alco-
hol on her breath. The initial laboratory profile included a hematolog-
ical analysis that showed that she had an anemia with enlarged red
blood cells (macrocytic). A bone marrow aspirate confirmed the suspi-
cion that she has a megaloblastic anemia because it showed a greater
than normal number of red and white blood cell precursors, most of
which were larger than normal. Further analyses revealed that her
serum folic acid level was 2.9 ng/mL (normal = 6 to 15), her serum B12
level was 153 pg/mL (normal = 150 to 750), and her serum iron level
was normal.
The patient’s megaloblastic anemia is most likely caused by which of
the following?
A. A decreased synthesis of methionine
B. A decreased conversion of dUMP to dTMP
C. A decrease in the synthesis of phosphatidyl choline
D. A decrease in the levels of succinyl CoA
E. A decreased synthesis of dUTP
[3.2]
A patient presents with a urinary tract infection and is prescribed a
combination drug containing trimethoprim and sulfamethoxazole. These
drugs are effective because they do which of the following?
A. Bind to operons to prevent synthesis of bacterial mRNA
B. Block transport across bacterial cell walls
C. Inhibit bacterial synthesis of cobalamin (B12)
D. Inhibit bacterial synthesis of THF
E. Inhibit synthesis of phospholipids in bacteria
[3.3]
Methotrexate is often used as a chemotherapeutic agent to treat patients
with leukemia. This drug is effective because it inhibits cells in which
part of the cell cycle?
A. G1
phase
B. S phase
C. M phase
D. G2 phase
E. G0 phase
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