Unit 10: The Citric Acid Cycle and Oxidative Phosphorylation
Where most of a glucose molecule's energy actually gets extracted: a spinning loop of oxidations feeding a proton gradient that spins a molecular turbine.
6 topics · 23 questions
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Pyruvate Oxidation and the Citric Acid Cycle
- How it worksHow does pyruvate dehydrogenase strip off a carbon and attach what's left to coenzyme A?
- How it worksWalk me through the citric acid cycle's eight steps that regenerate oxaloacetate at the end of each loop.
- Common mistakeWhy isn't the citric acid cycle a linear pathway that starts and ends at completely different molecules?
- Worked exampleFind how many NADH molecules two turns of the citric acid cycle produce, given 3 NADH made per turn, to process one glucose's worth of pyruvate.
Your turn1 of 2
Find how many NADH molecules 4 turns of the citric acid cycle produce, given 3 NADH made per turn.Electron Carriers: NADH and FADH2
- How it worksHow does NAD+ pick up a pair of electrons and a proton to become NADH at each oxidation step?
- Common mistakeWhy isn't NADH itself the cell's spendable energy currency the way ATP is?
- Going furtherWhat happens to a cell's ATP output when its NAD+ pool becomes fully reduced and can't accept more electrons?
Your turn1 of 2
NADH is produced in large amounts throughout cellular respiration and carries substantial chemical energy. A student assumes NADH must be the cell's actual spendable energy currency, the same role ATP plays. Why isn't NADH itself the cell's spendable energy currency the way ATP is?The Electron Transport Chain
- How it worksHow does each complex in the electron transport chain pass electrons onward while pumping protons across the membrane?
- How it worksWalk me through how oxygen accepts electrons at the very end of the chain to form water.
- Worked exampleFind the total protons pumped per NADH oxidized through the electron transport chain, given about 4 at Complex I, 4 at Complex III, and 2 at Complex IV.
- Common mistakeWhy doesn't the electron transport chain make ATP directly, the way substrate-level phosphorylation does?
- Going furtherWhat happens to electron flow through the chain when a poison like cyanide blocks its final complex?
Your turn1 of 2
Find the total protons pumped per NADH oxidized through the electron transport chain, given about 5 at Complex I, 5 at Complex III, and 4 at Complex IV.Chemiosmosis and the Proton Motive Force
- How it worksHow does the electron transport chain pump protons into an increasingly acidic, positively charged compartment?
- How it worksHow does that stored gradient get released to drive ATP synthesis as protons flow back down it?
- Common mistakeWhy isn't the proton gradient just a side effect of electron transport rather than the actual point of it?
- Ties togetherHow does chemiosmosis link an electron transport chain that makes no ATP itself to an ATP synthase that never touches an electron?
Your turn1 of 2
As electrons move through the electron transport chain, protons get pumped across the inner mitochondrial membrane, building up a gradient. A student describes this proton gradient as just an incidental byproduct of moving electrons, with no real functional importance. Why isn't the proton gradient just a side effect of electron transport rather than the actual point of it?ATP Synthase as a Rotary Motor
- How it worksHow does a flow of protons through ATP synthase's channel spin its rotor ring?
- How it worksWalk me through how that spinning shaft forces conformational changes that assemble ATP from ADP and phosphate.
- Common mistakeWhy isn't ATP synthase simply using the protons themselves as a chemical ingredient built into ATP?
- Worked exampleFind how many ATP molecules are made per full rotation of an ATP synthase if each rotation yields 3 ATP for roughly every 10 protons.
Your turn1 of 2
Find how many ATP molecules are made from 90 protons flowing through ATP synthase, if each full rotation uses about 11 protons and yields 4 ATP.Calculating ATP Yield from Glucose Oxidation
- How it worksWalk me through totaling ATP from glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation for one glucose.
- Worked exampleFind the approximate total ATP yield per glucose molecule using a commonly cited estimate of about 30 to 32 ATP from full aerobic respiration.
- Common mistakeWhy isn't the ATP yield of aerobic respiration a fixed, universal number that's identical for every cell type?
Your turn1 of 2
A textbook lists the following ATP contributions from one glucose molecule's full aerobic breakdown: 3 net ATP from glycolysis, 2 ATP from substrate-level phosphorylation in the citric acid cycle, and 31 ATP from oxidative phosphorylation. Find the total ATP yield.