Cellular Respiration Overview

Vocabulary flashcards summarizing key terms, enzymes, pathways, and processes involved in cellular respiration and its alternatives.

Cellular Respiration

Series of metabolic pathways that oxidize glucose, funnel electrons to the ETC, and generate ATP (exergonic).

Glycolysis

Cytosolic pathway that breaks glucose into 2 pyruvate, netting 2 ATP and 2 NADH.

Substrate-Level Phosphorylation

Direct synthesis of ATP by transferring a phosphate group from a substrate molecule to ADP.

Hexokinase

Enzyme that phosphorylates glucose to glucose-6-phosphate; irreversible, traps glucose in the cell; uses 1 ATP.

Phosphofructokinase (PFK)

Rate-limiting glycolytic enzyme that adds a second phosphate, irreversibly committing the molecule to glycolysis.

Aerobic Respiration

Oxygen-dependent ATP production in which O2 serves as the final electron acceptor in the ETC.

Aerobic Respiration Equation

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP.

Anaerobic Respiration

ATP generation without oxygen; glycolysis followed by fermentation to regenerate NAD+.

NAD+ Regeneration

Re-oxidation of NADH to NAD+ (via ETC or fermentation) so glycolysis can continue.

Pyruvate Decarboxylation

Conversion of pyruvate to acetyl-CoA by the pyruvate dehydrogenase complex in the mitochondrial matrix.

Pyruvate Dehydrogenase Complex (PDC)

Multi-enzyme complex that removes CO2 from pyruvate and attaches CoA, producing acetyl-CoA and NADH.

Acetyl-CoA

Two-carbon carrier molecule that enters the Citric Acid Cycle to fuel oxidative metabolism.

Citric Acid Cycle (CAC) / Krebs Cycle

Mitochondrial matrix cycle that oxidizes acetyl-CoA to CO2 while generating NADH, FADH2, and ATP; regenerates oxaloacetate.

Oxaloacetate

Four-carbon molecule regenerated each turn of the CAC, enabling continuous cycling.

Electron Transport Chain (ETC)

Series of membrane proteins that transfer electrons from NADH/FADH2 to O2, pumping H+ to create a gradient.

Oxidative Phosphorylation

ATP production powered by the oxidation of electron carriers and the H+ gradient across the inner mitochondrial membrane.

Proton Motive Force

Electrochemical H+ gradient across the inner mitochondrial membrane that drives ATP synthesis.

ATP Synthase

Membrane enzyme that uses the proton motive force to convert ADP + Pi into ATP (chemiosmosis).

Alcohol Fermentation

Anaerobic pathway in yeast/plants: pyruvate → acetaldehyde + CO2 → ethanol, regenerating NAD+; acetaldehyde is the final electron acceptor.

Acetaldehyde

Intermediate and final electron acceptor in alcohol fermentation, reduced to ethanol.

Lactic Acid Fermentation

Anaerobic pathway in muscle cells/microbes: pyruvate is reduced to lactate, regenerating NAD+.

Cori Cycle

Transport of lactate from muscle to liver for conversion back to glucose when ATP becomes available.

Gluconeogenesis

Liver pathway that synthesizes glucose from non-carbohydrate precursors when glucose is scarce.

Glycogen

Branched glucose polymer stored mainly in liver and skeletal muscle as a rapid energy reserve.

Alternative Energy Sources

When glucose is low, cells catabolize other carbohydrates, fats, and then proteins to obtain ATP.