MCAT Biochemistry — Metabolism flashcards
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Glycolysis and fermentation, pyruvate dehydrogenase, the citric acid cycle, electron transport and oxidative phosphorylation, gluconeogenesis, glycogen, the pentose phosphate pathway, fatty acid synthesis and β-oxidation, ketone bodies, and the fed-versus-fasting hormones.
Learn deck · part of MCAT · written against: AAMC MCAT content outline (2015 exam, current through 2026). Updated 2026-10-10.
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Where in the cell does glycolysis take place, and what is the net yield from one glucose?In the cytosol. One glucose gives 2 pyruvate, 2 NADH and a net 2 ATP (4 ATP are made by substrate-level phosphorylation and 2 are spent in the priming steps).Glycolysis
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Why do cells ferment pyruvate when oxygen is scarce, given that fermentation itself produces no ATP?To regenerate NAD⁺. Without the electron transport chain, NADH would pile up and the glyceraldehyde-3-phosphate dehydrogenase step would stop; reducing pyruvate recycles NAD⁺ so glycolysis can keep yielding its 2 ATP.Fermentation
Watch out: yeast reaches the same goal in two steps, decarboxylating pyruvate to acetaldehyde and then reducing that to ethanol. -
What does one turn of the citric acid cycle produce from one acetyl-CoA?3 NADH, 1 FADH₂, 1 GTP (equivalent to ATP) and 2 CO₂. Since one glucose yields two acetyl-CoA, the cycle turns twice per glucose; it runs in the mitochondrial matrix.Citric Acid Cycle
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Where is the electron transport chain located, and what is the final electron acceptor?In the inner mitochondrial membrane. Electrons from NADH and FADH₂ pass along the complexes to oxygen, which Complex IV (cytochrome c oxidase) reduces to water.Electron Transport Chain
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According to the chemiosmotic model, how is electron transport coupled to ATP synthesis?The chain pumps protons out of the matrix, creating an electrochemical proton gradient (the proton-motive force) across the inner membrane. Protons flow back in through ATP synthase, whose membrane-embedded F₀ portion rotates as they pass and drives the F₁ portion in the matrix to join ADP and phosphate.Oxidative Phosphorylation
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How is glycogen built, and which enzymes do the work?Glycogen synthase adds glucose units from UDP-glucose to the non-reducing ends of the chain through α-1,4 linkages, starting from a primer protein called glycogenin. Branching enzyme then moves short segments onto the chain as α-1,6 branches, giving the molecule many ends for fast release.Glycogen
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What are the two products the pentose phosphate pathway exists to make?NADPH, the reducing power for fatty acid and cholesterol synthesis and for keeping glutathione reduced, and ribose-5-phosphate for nucleotide synthesis. It runs in the cytosol and makes no ATP.Pentose Phosphate Pathway
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Fatty acid synthesis happens in the cytosol, but acetyl-CoA is made in the mitochondria. How does it get out?As citrate: acetyl-CoA condenses with oxaloacetate, citrate crosses the inner membrane on a carrier, and cytosolic ATP-citrate lyase splits it back into acetyl-CoA and oxaloacetate. High cytosolic citrate therefore signals a well-fed cell and also activates acetyl-CoA carboxylase.Fatty Acid Synthesis
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What are the ketone bodies, and under what conditions does the liver make them?Acetoacetate, β-hydroxybutyrate and acetone, made in liver mitochondria from acetyl-CoA. They form during fasting, prolonged exercise or uncontrolled diabetes, when fat oxidation floods the liver with acetyl-CoA while oxaloacetate is being drawn off into gluconeogenesis.Ketone Bodies
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What does insulin do to carbohydrate, fat and protein metabolism in the fed state?It is the storage hormone: it moves GLUT4 to the surface of muscle and fat cells and stimulates glycogen synthesis, glycolysis, fatty acid synthesis and protein synthesis while suppressing gluconeogenesis, glycogenolysis and lipolysis. Pancreatic β cells release it when blood glucose rises.Fed vs Fasting Hormones
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Review status: Second-reader reviewed, with corrections applied.
Checked against:
- OpenStax Biology 2e and OpenStax Anatomy and Physiology 2e, consulted as references; no text copied.
- Facts cross-checked against Lehninger Principles of Biochemistry, 8th ed. (reference only; no text copied).
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