Cellular respiration is a process that oxidizes biological fuels using an inorganic electron acceptor like oxygen.
Drives the production of ATP (adenosine triphosphate), which stores chemical energy.
Described as metabolic reactions that convert nutrients to ATP, releasing waste products.
Types of Cellular Respiration
Aerobic Respiration: Uses oxygen as electron acceptor.
Anaerobic Respiration: Uses other molecules than oxygen. Includes fermentation but not considered respiration since no external electron acceptor is involved.
Main Stages of Aerobic Respiration
Glycolysis
Occurs in cytosol, splits glucose into two pyruvate molecules.
Generates 2 ATP and 2 NADH net gain (4 ATP produced, 2 consumed).
Oxidative Decarboxylation of Pyruvate
Converts pyruvate to acetyl-CoA and CO2.
Produces NADH in the process.
Citric Acid Cycle (Krebs Cycle)
Acetyl-CoA is oxidized in the mitochondrial matrix.
Produces NADH, FADH2, and GTP (converted to ATP).
Two acetyl-CoA per glucose molecule lead to 6 NADH, 2 FADH2, and 2 ATP.
Oxidative Phosphorylation
Involves the electron transport chain and chemiosmosis.
Produces the majority of ATP (approximately 30-32 ATP per glucose).
Efficiency of ATP Production
Theoretical yield is 38 ATP/glucose, but actual yield is about 29-30 ATP/glucose due to losses like leaky membranes and transport costs.
ATP yield varies due to differences in shuttle mechanisms (e.g., glycerol phosphate vs. malate-aspartate shuttle).
Fermentation
Occurs when oxygen is absent.
Pyruvate undergoes fermentation in cytoplasm, producing waste products like lactic acid or ethanol.
Only 2 ATP produced per glucose through substrate-level phosphorylation.
Anaerobic Respiration
Uses inorganic electron acceptors other than oxygen (e.g., sulfate, nitrate).
Found in organisms in environments void of oxygen, like underwater caves or anoxic soils.
Key Points
Aerobic respiration is more efficient than anaerobic, producing more ATP per glucose.
The electron transport chain and chemiosmosis are pivotal in ATP synthesis.
Different pathways like glycolysis and the citric acid cycle contribute to the overall energy yield.
References
Various sources and studies cited within the text provide detailed insights into specific biochemical processes involved in cellular respiration.