USMLE Biochemistry 2

Question 1

A child presents with megaloblastic anemia and homocystinuria but normal methylmalonic acid levels. Which vitamin deficiency is most likely?

Accepted Answer

Folate

Answer

Vitamin B12

Answer

Vitamin B6

Answer

Vitamin B2

Question 2

Which glycogen storage disease presents with hypoglycemia, lactic acidosis, and hepatomegaly due to glucose-6-phosphatase deficiency?

Accepted Answer

Von Gierke disease (Type I)

Answer

Pompe disease (Type II)

Answer

Cori disease (Type III)

Answer

McArdle disease (Type V)

Question 3

In the citric acid cycle, which reaction is catalyzed by isocitrate dehydrogenase?

Accepted Answer

Isocitrate → alpha-ketoglutarate + CO2

Answer

Citrate → isocitrate

Answer

Alpha-ketoglutarate → succinyl-CoA

Answer

Succinate → fumarate

Question 4

Alkaptonuria is caused by a deficiency of which enzyme?

Accepted Answer

Homogentisate oxidase

Answer

Phenylalanine hydroxylase

Answer

Tyrosine aminotransferase

Answer

Fumarylacetoacetate hydrolase

Question 5

Which lipoprotein is primarily responsible for reverse cholesterol transport?

Accepted Answer

HDL

Answer

LDL

Answer

VLDL

Answer

Chylomicrons

Question 6

Lesch-Nyhan syndrome is caused by deficiency of which enzyme?

Accepted Answer

HGPRT (hypoxanthine-guanine phosphoribosyltransferase)

Answer

Adenosine deaminase

Answer

Purine nucleoside phosphorylase

Answer

Xanthine oxidase