Cellular Respiration and Fermentation — Notes

Vocabulary flashcards covering key terms and definitions from the lecture notes on cellular respiration, fermentation, and related metabolic concepts.

Cellular respiration

Process by which cells extract energy from organic molecules (usually glucose) to produce ATP, typically via glycolysis, the citric acid cycle, and oxidative phosphorylation; can be aerobic or anaerobic.

Fermentation

Partial breakdown of sugars without O2 that regenerates NAD+ to allow glycolysis to continue, yielding only about 2 ATP per glucose; end products include ethanol or lactate.

Glycolysis

Pathway in the cytosol that breaks glucose into two pyruvate molecules, producing net 2 ATP and 2 NADH; occurs with or without O2.

Glycolysis—Energy Investment Phase

Phase in which ATP is invested to phosphorylate glucose and prepare intermediates.

Glycolysis—Energy Payoff Phase

Phase in which ATP and NADH are produced as intermediates are oxidized to pyruvate.

Pyruvate

End product of glycolysis; in aerobic conditions, transported into mitochondria for further oxidation to CO2 and water.

Pyruvate oxidation

Conversion of pyruvate to acetyl CoA in the mitochondria, releasing CO2 and generating NADH.

Acetyl CoA

Coenzyme A–acetyl group that enters the citric acid cycle to begin its oxidation.

Citric acid cycle (Krebs cycle)

Cycle that fully oxidizes acetyl CoA, yielding per turn: 1 ATP (GTP), 3 NADH, and 1 FADH2 in the mitochondrial matrix.

Oxidative phosphorylation

Stage where most ATP is produced; electron transport chain plus chemiosmosis using a proton gradient to synthesize ATP.

Electron transport chain (ETC)

Series of protein complexes in the inner mitochondrial membrane that transfer electrons from NADH/FADH2 to O2, releasing energy in steps.

Chemiosmosis

Process by which a proton gradient drives the synthesis of ATP via ATP synthase.

Proton-motive force

Energy stored in a proton (H+) gradient across a membrane that powers ATP synthesis and other work.

ATP synthase

Enzyme that uses the flow of protons down their gradient to phosphorylate ADP to ATP.

NAD+/NADH

NAD+ is an electron carrier; NADH is the reduced form that donates electrons to the electron transport chain.

FAD/FADH2

FAD accepts electrons to become FADH2; donates electrons to the electron transport chain.

NADH shuttle

Systems (e.g., malate-aspartate or glycerol phosphate) that transfer electrons from cytosolic NADH into mitochondria.

Redox reactions

Oxidation-reduction reactions involving transfer of electrons that release energy used to synthesize ATP.

Oxidation

Loss of electrons by a substance; oxidation state increases.

Reduction

Gain of electrons by a substance; reduction state increases.

Reducing agent

Substance that donates electrons in a redox reaction.

Oxidizing agent

Substance that accepts electrons in a redox reaction.

Oxygen as final electron acceptor

In aerobic respiration, O2 accepts electrons at the end of the ETC, forming water.

Mitochondrion

Organelle where most of cellular respiration occurs, housing the ETC and Krebs cycle.

Mitochondrial matrix

Innermost space of the mitochondrion where the Krebs cycle takes place and pyruvate is oxidized.

Inner mitochondrial membrane (cristae)

Membrane where the ETC resides; folds (cristae) increase surface area for respiration.

Substrate-level phosphorylation

Direct synthesis of ATP from ADP and a high-energy phosphate group during glycolysis and the Krebs cycle.

Aerobic respiration

Cellular respiration that uses O2 as the final electron acceptor, yielding large amounts of ATP.

Anaerobic respiration

Respiration using an ETC with a final electron acceptor other than O2 (e.g., sulfate).

Fermentation types

Two common types: alcoholic fermentation (ethanol + CO2) and lactic acid fermentation (lactate).

Alcoholic fermentation

Pyruvate is converted to ethanol with CO2 release; used in brewing, baking, winemaking.

Lactic acid fermentation

Pyruvate is reduced to lactate; regenerates NAD+; used in cheese/yogurt production and in muscle cells under low O2.

Obligate anaerobe

Organism that cannot survive in the presence of O2 and relies on fermentation or anaerobic respiration.

Facultative anaerobe

Organism that can use either fermentation or cellular respiration depending on O2 availability.

Beta-oxidation

Breakdown of fatty acids in mitochondria to generate acetyl CoA for the Krebs cycle.

Glycolysis location

Occurs in the cytosol, independent of O2 availability.

Catabolic pathways

Pathways that break down molecules to release energy (e.g., glycolysis, Krebs cycle, ETC).

Anabolic pathways

Pathways that synthesize complex molecules from simpler ones, using energy.

Feedback inhibition

Regulatory mechanism where ATP levels control respiration; high ATP slows, low ATP speeds up.

ATP yield per glucose

Energy yield from glucose varies; notes cite up to 38 ATP (max), commonly ~32 ATP, or about 30–32 ATP in many estimates.

Photosynthesis (brief)

Process that captures light energy to synthesize organic molecules and release O2, occurring in chloroplasts.