Biochemistry Flashcards
6 cards from real USMLE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Biochemistry flashcards as text
A child presents with megaloblastic anemia and homocystinuria but normal methylmalonic acid levels. Which vitamin deficiency is most likely?
Answer: Folate
Folate deficiency causes megaloblastic anemia and elevated homocysteine but does not cause methylmalonic aciduria, distinguishing it from B12 deficiency.
Which glycogen storage disease presents with hypoglycemia, lactic acidosis, and hepatomegaly due to glucose-6-phosphatase deficiency?
Answer: Von Gierke disease (Type I)
Von Gierke disease (Type Ia) results from glucose-6-phosphatase deficiency, preventing glucose release from the liver and causing hypoglycemia with lactic acidosis.
In the citric acid cycle, which reaction is catalyzed by isocitrate dehydrogenase?
Answer: Isocitrate → alpha-ketoglutarate + CO2
Isocitrate dehydrogenase catalyzes the oxidative decarboxylation of isocitrate to alpha-ketoglutarate, producing CO2 and NADH.
Alkaptonuria is caused by a deficiency of which enzyme?
Answer: Homogentisate oxidase
Alkaptonuria results from homogentisate oxidase deficiency, causing accumulation of homogentisic acid, which causes dark urine and ochronosis.
Which lipoprotein is primarily responsible for reverse cholesterol transport?
Answer: HDL
HDL mediates reverse cholesterol transport by collecting cholesterol from peripheral tissues and delivering it to the liver for excretion.
Lesch-Nyhan syndrome is caused by deficiency of which enzyme?
Answer: HGPRT (hypoxanthine-guanine phosphoribosyltransferase)
Lesch-Nyhan syndrome results from HGPRT deficiency, impairing purine salvage and leading to gout, intellectual disability, and self-mutilation.