Aerobic Metabolism

Animal cells use two main mechanisms to produce ATP. When oxygen is present, most cells are able to produce ATP by aerobic respiration. When ATP is absent, some animal cells are able to catabolize glucose anaerobically. Aerobic respiration involves three major processes: glycolysis, the Kreb's (tricarboxylic acid or TCA) cycle, and oxidative phosphorylation coupling the electron transport chain in the mitochondria with chemiosmosis. Aerobic catabolism of glucose requires oxygen and produces carbon dioxide and metabolic water. Anaerobic glucose catabolism in animal cells involves only glycolysis and the reduction of pyruvate to lactate. Anaerobic catabolism does not require oxygen and does not produce carbon dioxide in animal cells. Aerobic catabolism is much more efficient at making ATP, yielding a net production of 38 ATP in some cells, compared to anaerobic respiration, which only yields a net production of 2 ATP. Skeletal muscle can also produce limited amounts of ATP from the breakdown of stored phosphocreatine (phosphogen system). This mechanism can produce 1 ATP for every molecule of phosphocreatine present.

The hexose (6-carbon sugar) known as glucose is the substrate of choice for ATP production and can be "burned" aerobically or anaerobically. Fructose and galactose are also hexoses and can be converted to glucose in cells with the appropriate enzymes. In humans, this conversion is accomplished by the liver. Some cells, such as neurons, are only able to use glucose. Other cells, such as cardiac and skeletal muscle, can also use glycerol and fatty acids from fats or amino acids that have been deaminated.

View the animations:
Glycolysis	Kreb's (TCA) Cycle	Electron Transport Chain and Chemiosmosis
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Written by J. Ellen Lathrop-Davis, M.Sc.
CCBC - Catonsville
Summer Grant, 2002
All Rights Reserved