MCAT Biological and Biochemical Foundations of Living Systems Flashcards: 1d Tca Cycle Oxidative Phosphorylation

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This deck focuses on 1d Tca Cycle Oxidative Phosphorylation, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

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Flashcard 1: What enzyme complex converts pyruvate to acetyl-CoA and links glycolysis to the citric acid cycle?

Answer: Pyruvate dehydrogenase complex (PDC). This complex decarboxylates pyruvate, linking glycolysis to the TCA cycle by producing acetyl-CoA for entry into the cycle.

Flashcard 2: Which direction do protons flow through ATP synthase to drive ATP formation in mitochondria?

Answer: Intermembrane space $ightarrow$ matrix. Protons flow down their electrochemical gradient from intermembrane space to matrix, driving ATP synthase's conformational changes for ATP production.

Flashcard 3: Using $2.5$ ATP per NADH and $1.5$ ATP per FADH$_2$, what ATP is produced from $3$ NADH and $1$ FADH$_2$?

Answer: $9.0$ ATP. Each NADH yields approximately 2.5 ATP and each FADH$_2$ yields 1.5 ATP through oxidative phosphorylation efficiency.

Flashcard 4: Which citric acid cycle enzyme catalyzes citrate to isocitrate via a dehydration/rehydration isomerization?

Answer: Aconitase. Aconitase isomerizes citrate to isocitrate through cis-aconitate intermediate, preparing for subsequent decarboxylation.

Flashcard 5: Which citric acid cycle step produces the first NADH and releases CO$_2$ (oxidative decarboxylation of isocitrate)?

Answer: Isocitrate dehydrogenase. This enzyme catalyzes the rate-limiting oxidative decarboxylation of isocitrate to $alpha$-ketoglutarate, generating NADH and releasing CO$_2$.

Flashcard 6: Which citric acid cycle step converts $ext{alpha}$-ketoglutarate to succinyl-CoA while producing NADH and CO$_2$?

Answer: $ext{alpha}$-ketoglutarate dehydrogenase complex. The complex performs oxidative decarboxylation, analogous to pyruvate dehydrogenase, producing succinyl-CoA, NADH, and CO$_2$.

Flashcard 7: Which citric acid cycle step produces GTP (or ATP) by substrate-level phosphorylation?

Answer: Succinyl-CoA synthetase (succinate thiokinase). This enzyme cleaves the thioester bond of succinyl-CoA, coupling it to phosphorylation of GDP to GTP or ADP to ATP.

Flashcard 8: Which citric acid cycle enzyme produces FADH$_2$ by oxidizing succinate to fumarate?

Answer: Succinate dehydrogenase (Complex II). As part of the ETC, this enzyme oxidizes succinate to fumarate, reducing FAD to FADH$_2$ for electron transfer.

Flashcard 9: Which citric acid cycle enzyme oxidizes malate to oxaloacetate and produces NADH?

Answer: Malate dehydrogenase. This enzyme regenerates oxaloacetate by oxidizing malate, reducing NAD$^+$ to NADH in the final step of the cycle.

Flashcard 10: Identify the total reduced electron carriers produced per glucose from two citric acid cycle turns (excluding PDC).

Answer: $6$ NADH and $2$ FADH$_2$. Two acetyl-CoA from one glucose enter two cycles, each producing 3 NADH and 1 FADH$_2$, totaling these carriers.

Flashcard 11: What are the net products of pyruvate dehydrogenase per pyruvate molecule?

Answer: $1$ acetyl-CoA, $1$ NADH, $1$ CO$_2$. Pyruvate is oxidatively decarboxylated, yielding acetyl-CoA for the TCA cycle, NADH as an electron carrier, and CO$_2$ as a byproduct.

Flashcard 12: What is the primary cellular location of the citric acid cycle in eukaryotes?

Answer: Mitochondrial matrix. The citric acid cycle occurs in the mitochondrial matrix where enzymes and substrates are concentrated for efficient metabolic processing.

Flashcard 13: What is the name of the enzyme that uses the proton gradient to synthesize ATP?

Answer: ATP synthase (Complex V). ATP synthase harnesses the proton gradient's energy via rotational catalysis to phosphorylate ADP to ATP.

Flashcard 14: What happens to oxidative phosphorylation if O$_2$ is absent and the ETC cannot pass electrons to Complex IV?

Answer: ETC stops, NADH accumulates, ATP synthase halts. Without O$_2$ as terminal acceptor, electron flow halts, preventing NADH oxidation and proton gradient maintenance for ATP synthesis.

Flashcard 15: Which citric acid cycle enzyme catalyzes the formation of citrate from oxaloacetate and acetyl-CoA?

Answer: Citrate synthase. This enzyme catalyzes the irreversible condensation reaction, committing acetyl-CoA to the citric acid cycle.

Flashcard 16: Which citric acid cycle enzyme hydrates fumarate to malate?

Answer: Fumarase (fumarate hydratase). Fumarase adds water across the double bond of fumarate, stereospecifically forming L-malate in a reversible hydration reaction.

Flashcard 17: What are the net products of one turn of the citric acid cycle per acetyl-CoA?

Answer: $3$ NADH, $1$ FADH$_2$, $1$ GTP, $2$ CO$_2$. One acetyl-CoA through the cycle yields reduced cofactors for ETC, GTP for energy, and CO$_2$ as waste.

Flashcard 18: What is the overall purpose of the electron transport chain in oxidative phosphorylation?

Answer: Create a proton-motive force by pumping H$^+$. The ETC transfers electrons from reduced carriers to O$_2$, using energy to pump protons and establish a gradient for ATP synthesis.

Flashcard 19: What is the final electron acceptor of the mitochondrial electron transport chain?

Answer: O$_2$ (reduced to H$_2$O). Oxygen accepts electrons from cytochrome c oxidase, forming water and preventing electron backup in the chain.

Flashcard 20: Which electron transport chain complexes pump protons across the inner mitochondrial membrane?

Answer: Complexes I, III, and IV. These complexes use electron transfer energy to translocate protons into the intermembrane space, creating the electrochemical gradient.

Flashcard 21: Which electron transport chain complex accepts electrons from NADH?

Answer: Complex I (NADH dehydrogenase). Complex I oxidizes NADH to NAD$^+$, transferring electrons to ubiquinone while pumping protons across the membrane.

Flashcard 22: Which electron transport chain complex accepts electrons from FADH$_2$ generated by succinate dehydrogenase?

Answer: Complex II (succinate dehydrogenase). Complex II directly feeds electrons from FADH$_2$ into the ubiquinone pool without pumping protons itself.

Flashcard 23: What are the two mobile electron carriers that shuttle electrons between ETC complexes?

Answer: Coenzyme Q (ubiquinone) and cytochrome $c$. These carriers facilitate electron transfer: ubiquinone between I/II and III, cytochrome c between III and IV.

Flashcard 24: What molecule condenses with acetyl-CoA to form citrate in the first step of the citric acid cycle?

Answer: Oxaloacetate. Oxaloacetate serves as the acceptor for the acetyl group from acetyl-CoA, initiating the cycle by forming citrate.