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How Cells Make ATP: Energy-Releasing Pathways. Cellular respiration Aerobic respiration Requires molecular oxygen Includes redox reactions Anaerobic Anaerobic respiration Fermentation Do not require oxygen All exergonic. Four stages of aerobic respiration Takes place in the cytosol
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Cellular respiration • Aerobic respiration • Requires molecular oxygen • Includes redox reactions • Anaerobic • Anaerobic respiration • Fermentation • Do not require oxygen • All exergonic
Four stages of aerobic respiration • Takes place in the cytosol • Glycolysis • Takes place in the mitochondrion • Formation of acetyl CoA • Citric acid cycle • Electron transport chain/chemiosmosis
Glycolysis • “Sugar splitting” • Does not require oxygen • Divided into two major phases • Energy investment phase • Energy capture phase • Each glucose molecule produces net yield of two NADH molecules and two ATP molecules
Glycolysis: energy investment phase
Glycolysis: energy capture phase
Formation of acetyl CoA • Catalyzed by enzyme pyruvate dehydrogenase • First carboxyl group is split off as carbon dioxide • Then remaining two-carbon fragment is oxidized and electrons transferred to NAD+ • Finally, oxidized two-carbon group is attached to coenzyme A
Citric acid cycle • For every glucose, two acetyl groups enter the citric acid cycle • Each two-carbon acetyl group combines with a four-carbon compound • Two CO2 molecules are removed • Energy captured as one ATP, three NADH, and one FADH2 per acetyl group
Electron transport chain • Series of electron carriers • Each carrier exists in oxidized or reduced form • Electrons pass down the electron transport chain in series of redox reactions • Lose energy as pass along the chain
Energyyield fromcompleteoxidation ofglucose byaerobicrespiration
Many organisms depend on nutrients other than glucose • Products of protein and lipid catabolism enter same metabolic pathways as glucose • Amino acids are deaminated
Anaerobic respiration versus fermentation • Anaerobic respiration • Electrons transferred from fuel molecules to electron transport chain • Final electron acceptor is inorganic substance • Fermentation • Anaerobic process that does not use electron transport chain
Comparison of aerobic respiration, anaerobic respiration, and fermentation