The pyruvate dehydrogenase complex is an enzyme complex that consists of 3 enzymes, which work together to catalyze the pyruvate decarboxylation reaction, where pyruvate is converted to acetyl CoA.

Pyruvate decarboxylation occurs in the mitochondrial matrix. The acetyl CoA produced from the pyruvate decarboxylation reaction will undergo the Citric Acid cycle also in the mitochondrial matrix.

During glycolysis, for each molecule of glucose, two molecules of pyruvate are produced ( glucose+ NAD+ + 2 ADP + 2Pi-> 2 pyruvate+ 2 ATP + 2NADH+. These 2 molecules of pyruvate then undergo the pyruvate decarboxylation reaction: 2(pyruvate+ CoA-SH+ NAD+ -> NADH+ CO2+ acetyl CoA).

During the pyruvate decarboxylation reaction , a thioester bond links the acetyl group of pyruvate with coenzyme A to produce acetyl CoA.

The pyruvate decarboxylation reaction is pyruvate+ CoA-SH+ NAD+ -> NADH+ CO2+ acetyl CoA.

Oxygen is the final electron acceptor in aerobic respiration. It becomes water upon being reduced by the accepted electrons, which explains why water is one of the products of respiration. Without the presence of oxygen, electrons would remain trapped and bound in the final step of the electron transport chain, preventing further reaction.

NADH and FADH₂ are necessary to donate electrons to the electron transport chain.

Aerobic cellular respiration is the process of breaking down glucose  to form intermittent electron electron carriers, which eventually donate their electrons to the final electron acceptor, oxygen, at the end of the electron transport chain. This process produces usable energy in the form of ATP, as well as waste produced of carbon dioxide and water.

One way to divide prokaryotes is into aerobes and anaerobes. Aerobes are organisms that can survive and grow in the presence of oxygen while anaerobes did not require oxygen for survival and growth. All aerobes can produce ATP with or without oxygen (though they may need oxygen for survival. However some anaerobes are harmed by the presence of oxygen (obligate anaerobes). These anaerobes can produce ATP through glycolysis or anaerobic respiration, where another molecule besides oxygen is used as the final electron acceptor for the electron transport chain.

If no oxygen is available, anaerobic respiration will occur. This can either be lactic acid fermentation, or alcoholic fermentation. In alcoholic or lactic acid fermentation, the pyruvate are decarboxylated and ultimately used to produce either ethanol or lactic acid, and regenerate NAD+ which will be reused for another cycle of glycolysis (2 ATP are produced for each round of glycolysis).

If no oxygen is available, anaerobic respiration will occur. This can either be lactic acid fermentation, or alcoholic fermentation. In alcoholic or lactic acid fermentation, the pyruvate are decarboxylated and ultimately used to produce either ethanol or lactic acid, and regenerate NAD+ which will be reused for another cycle of glycolysis (2 ATP are produced for each round of glycolysis).