Citric Acid Cycle, Oxidative Phosphorylation and Fatty Acid Oxidation: every key term you need (+ practice quiz)
25 flashcard terms for Biochemistry Topic 7, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
A multienzyme assembly that oxidatively decarboxylates pyruvate to an acetyl unit. The step is irreversible, which is why fatty acids cannot be converted back to glucose.
Citrate synthase
Condenses an acetyl unit with a four-carbon acceptor to open the cycle. It is inhibited by its product and by high energy charge.
Isocitrate dehydrogenase
The principal rate-limiting oxidative decarboxylation of the cycle, activated when energy charge falls and inhibited when it rises.
Alpha-ketoglutarate dehydrogenase
The second oxidative decarboxylation, mechanistically similar to the pyruvate complex and inhibited by its own products.
Succinyl-CoA synthetase
The only step of the cycle that produces a nucleoside triphosphate directly, by substrate-level phosphorylation.
Succinate dehydrogenase
The one cycle enzyme embedded in the inner membrane, feeding its electrons straight into the transport chain through a flavin carrier.
Anaplerotic reaction
Replenishes cycle intermediates drained for biosynthesis. Without it, withdrawing intermediates would stall the cycle for lack of the acetyl acceptor.
Amphibolic pathway
A pathway serving both breakdown and biosynthesis. The citric acid cycle both oxidizes fuel and supplies carbon skeletons for amino acids and heme.
Electron transport chain
A series of membrane complexes passing electrons down a redox gradient to oxygen, using the released energy to pump protons across the inner membrane.
Ubiquinone
A small lipid-soluble carrier that diffuses within the membrane, collecting electrons from several dehydrogenases and delivering them onward.
Cytochrome c
A small soluble carrier in the intermembrane space that shuttles single electrons between complexes. Its release into the cytosol also triggers programmed cell death.
Proton motive force
The combined charge and pH gradient across the inner membrane. It stores the energy of oxidation until the synthase converts it into chemical bonds.
Chemiosmotic theory
States that electron transport and phosphate bond synthesis are coupled by a proton gradient rather than a shared chemical intermediate, which is why an intact membrane is essential.
ATP synthase
A rotary motor whose membrane sector turns as protons flow through, driving conformational cycles in the catalytic head that release the newly formed product.
Uncoupler
A compound that carries protons across the membrane, dissipating the gradient. Electron transport accelerates but produces heat instead of usable phosphate bonds.
Respiratory control
The dependence of electron transport rate on nucleoside diphosphate availability. Without demand the gradient builds and pumping stalls.
Malate-aspartate shuttle
Moves cytosolic reducing equivalents into the mitochondrion without moving the carrier itself, preserving their full yield.
Glycerol phosphate shuttle
An alternative transfer route that delivers electrons at a lower point in the chain, giving a smaller yield but running faster.
Shortens a fatty acyl chain by two carbons per cycle through oxidation, hydration, oxidation and thiolysis, producing one acetyl unit and two reduced carriers each round.
Carnitine shuttle
Carries long-chain acyl groups across the inner mitochondrial membrane. It is the committed and rate-limiting step of fatty acid oxidation.
Malonyl-CoA inhibition
The first committed intermediate of fatty acid synthesis blocks the carnitine shuttle, preventing simultaneous synthesis and oxidation of fatty acids.
Odd-chain fatty acid oxidation
Ends in a three-carbon unit that is carboxylated and rearranged into a cycle intermediate, making it the small part of a fatty acid that can yield glucose.
Unsaturated fatty acid oxidation
Requires an isomerase and a reductase to handle existing double bonds, so the overall yield is slightly lower than for the saturated equivalent.
Ketogenesis
Converts excess acetyl units in liver mitochondria into circulating ketone bodies during fasting, providing fuel that the brain can use in place of glucose.
Reactive oxygen species
Partially reduced oxygen leaking from the transport chain. Superoxide dismutase, catalase and glutathione peroxidase form the main defence.