Glycolysis

• Glycolysis is the breakdown of glucose to pyruvate in the cytoplasm.
• ATP is required for the phosphorylation of glucose and intermediates during the energy investment phase of glycolysis.
• This leads to the generation of more ATP during the energy pay-off stage and results in a net gain of ATP.
• In aerobic conditions pyruvate is broken down to an acetyl group that combines with coenzyme A forming acetyl coenzyme A.

Citric Acid Cycle

• In the citric acid cycle the acetyl group from acetyl coenzyme A combines with oxaloacetate to form citrate.
• During a series of enzyme controlled steps, citrate is gradually converted back into oxaloacetate which results in the generation of ATP and release of carbon dioxide.
• The citric acid cycle occurs in the matrix of the mitochondria.
• Dehydrogenase enzymes remove hydrogen ions and electrons and pass them to the coenzyme NAD, forming NADH.
• This occurs in both glycolysis and the citric acid cycle.
• The hydrogen ions and electrons from NADH are passed to the electron transport chain on the inner mitochondrial membrane.

The Electron Transport Chain and ATP synthesis

• The electron transport chain is a series of carrier proteins attached to the inner mitochondrial membrane.

ATP synthesis

• Electrons are passed along the electron transport chain releasing energy.
• This energy allows hydrogen ions to be pumped across the inner mitochondrial membrane.
• The flow of these ions back through the membrane protein ATP synthase results in the production of ATP.
• Finally, hydrogen ions and electrons combine with oxygen to form water.