Biochemistry Flashcards
7 cards from real MCAT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Biochemistry flashcards as text
Which of the following correctly describes the function of GLUT2 transporters in pancreatic beta cells?
Answer: They have high Km and high capacity, allowing beta cells to sense elevated blood glucose
GLUT2 has a high Km (~15-20 mM) and high Vmax, so glucose uptake into beta cells is proportional to blood glucose concentration, coupling glucose sensing to insulin secretion.
Alkaptonuria is caused by accumulation of homogentisate due to deficiency of:
Answer: Homogentisate oxidase
Homogentisate oxidase deficiency leads to accumulation of homogentisic acid, which polymerizes and deposits in connective tissues causing ochronosis and dark urine.
Which of the following amino acids is both glucogenic and ketogenic?
Answer: Isoleucine
Isoleucine is both glucogenic and ketogenic, as its catabolism yields succinyl-CoA (glucogenic) and acetyl-CoA (ketogenic).
During prolonged fasting, the brain adapts by using which alternative fuel source?
Answer: Ketone bodies (acetoacetate and β-hydroxybutyrate)
After several days of fasting, the brain shifts to using ketone bodies derived from hepatic fatty acid oxidation, reducing its glucose requirement by up to 75%.
In the lac operon, the CAP-cAMP complex acts as a:
Answer: Positive regulator that enhances transcription when glucose is absent
When glucose is low, cAMP rises and binds CAP (catabolite activator protein), and the complex binds the lac promoter to enhance RNA polymerase binding and increase transcription.
Zymogen activation of pepsinogen to pepsin in the stomach occurs via:
Answer: Autocatalytic cleavage at low pH
Pepsinogen undergoes autocatalytic activation at gastric pH below 5, cleaving its inhibitory propeptide to form active pepsin.
Which of the following correctly pairs a metabolic pathway with its subcellular location in eukaryotes?
Answer: Heme synthesis — both mitochondria and cytoplasm
Heme synthesis begins and ends in the mitochondria (ALA synthesis and final steps), with intermediate steps occurring in the cytoplasm.