unit 2 - ka2: cellular respiration

• 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.
• 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.
• ATP synthesis — electrons are passed along the electron transport chain releasing energy.
• The electron transport chain is a series of carrier proteins attached to the inner mitochondrial membrane.
• 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.
• Fermentation - In the absence of oxygen, fermentation takes place in the cytoplasm.
• In animal cells, pyruvate is converted to lactate in a reversible reaction.
• In plants and yeast, ethanol and CO2 are produced in an irreversible reaction.
• Fermentation results in much less ATP being produced than in aerobic respiration.
• ATP is used to transfer energy to cellular processes which require energy.