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
Which enzyme is deficient in phenylketonuria (PKU)?
Answer: Phenylalanine hydroxylase
PKU is caused by deficiency of phenylalanine hydroxylase, which converts phenylalanine to tyrosine.
A patient with jaundice, hemolytic anemia, and splenomegaly has a G6PD deficiency. Which pathway is primarily affected?
Answer: Hexose monophosphate shunt
G6PD deficiency impairs the hexose monophosphate shunt, reducing NADPH and glutathione regeneration needed to protect RBCs from oxidative damage.
Which vitamin is a cofactor for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase?
Answer: Thiamine (B1)
Thiamine (B1) as thiamine pyrophosphate (TPP) is essential for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase reactions.
Maple syrup urine disease results from deficiency of which enzyme?
Answer: Branched-chain alpha-ketoacid dehydrogenase
Maple syrup urine disease is caused by deficiency of branched-chain alpha-ketoacid dehydrogenase, leading to accumulation of leucine, isoleucine, and valine.
In the urea cycle, which amino acid donates the second nitrogen atom incorporated into urea?
Answer: Aspartate
Aspartate donates the second nitrogen to form argininosuccinate in the urea cycle, ultimately contributing one nitrogen to urea.
Which enzyme catalyzes the rate-limiting step of fatty acid synthesis?
Answer: Acetyl-CoA carboxylase
Acetyl-CoA carboxylase catalyzes the conversion of acetyl-CoA to malonyl-CoA, which is the rate-limiting step of fatty acid synthesis.