Deck · USMLE Step 1
Foundational Sciences (General Principles)
Biochemistry, molecular biology, genetics, cell biology, and the general principles of microbiology, immunology, and pharmacology underlying every organ system.
188 cards · audited · SM-2 spaced repetition
Included with the full USMLE Step 1 program — 14 decks, 1,546 cards.
Sample cards
What is the rate-limiting (committed) step of glycolysis, and which enzyme catalyzes it?
The conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, catalyzed by phosphofructokinase-1 (PFK-1). It is allosterically activated by AMP and fructose-2,6-bisphosphate, and inhibited by ATP and citrate.
Which glycolytic enzyme is the only one unique to the liver/pancreatic β-cells and not inhibited by its product?
Glucokinase. It has a high Km (low affinity) and high Vmax, is not inhibited by glucose-6-phosphate, and is induced by insulin — letting the liver sequester glucose only when blood glucose is high.
How many net ATP are produced per glucose in aerobic glycolysis (glucose to 2 pyruvate)?
Net 2 ATP and 2 NADH per glucose. Substrate-level: 4 ATP made (phosphoglycerate kinase, pyruvate kinase steps) minus 2 ATP consumed (hexokinase/glucokinase and PFK-1 steps).
Why do mature red blood cells rely exclusively on anaerobic glycolysis?
RBCs lack mitochondria, so they cannot perform oxidative phosphorylation or the TCA cycle. They regenerate NAD+ by converting pyruvate to lactate via lactate dehydrogenase, producing only 2 net ATP per glucose.
What is the function of the 2,3-bisphosphoglycerate (2,3-BPG) shunt in RBCs?
The Rapoport-Luebering shunt diverts 1,3-BPG to 2,3-BPG (bypassing an ATP-generating step). 2,3-BPG binds deoxyhemoglobin and decreases its O2 affinity, shifting the oxyhemoglobin curve right to favor O2 unloading in tissues.
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