Cellular Respiration

What are the steps involved in cellular respiration?

Cellular respirationglossary term (opens in a new window) is how cells get energy from food. Simple sugars, like glucose are broken down to release energy. This process takes place in many small steps.The energy released is used to make ATP:

• Aerobic cellular respiration uses glucose and oxygen. It produces carbon-dioxide, water, and ATP.
• ATP is a high energy molecule that provides energy to cell processes.
• Cellular respiration has three main stages: glycolysisglossary term (opens in a new window), the Krebs Cycle, and the electron transport chainglossary term (opens in a new window).
• Each stage of cellular respiration involves a series of chemical reactions.
• These reactions are redox reactions. A redox reaction includes an electron acceptor (oxidizing agentglossary term (opens in a new window)) and an electron donor (reducing agentglossary term (opens in a new window)).
• Glycolysis is the first stage of cellular respiration. It does not use oxygen. In glycolysis  one glucose molecule and two molecules of ATP are used. 2 pyruvate, 4 ATP, and 2 NADH molecules are made. (NADH is a high energy molecule that provides electrons to some cell processes.)
• Pyruvate made in glycolysis is transported into the mitochondria. There it is converted into acetyl CoA.
• Acetyl CoA then enters a series of eight chemical reactions called the Krebs cycle. CoA combines with another reactant. The Krebs cycle produces 1 ATP, 3 NADH, and 1 FADH₂ molecules.
• NADH and FADH₂ donate electrons to the electron transport chain.
• The electron transport chain consists of a series of protein complexes. It is found in the inner mitochondrial membrane.
• Donated electrons pass down the chain, releasing energy with each step. The released energy is used to make more ATP.
• Electrons passing down the chain are received by the final electron acceptor. In aerobic respirationglossary term (opens in a new window) this is oxygen. This oxygen combines with an extra electron and hydrogen ions to form water.
• Aerobic respiration of one molecule of glucose produces a total of 36 molecules of ATP.

What are the differences between aerobic and anaerobic respiration?

Anaerobic respirationglossary term (opens in a new window) produces ATP without oxygen:

• Cells that live in oxygen-poor environments or are working under low-oxygen circumstances can use anaerobic respiration.
• In anaerobic respiration, molecules other than oxygen serve as the final electron acceptor. These include nitrate, sulfate, or sulfur.
• Fermentationglossary term (opens in a new window) is one form of anaerobic ATP production. During fermentation, only glycolysis takes place.  The Krebs cycle or electron transport chain do not take place.
• Fermentation involves the conversion of pyruvate to a different molecule. Pyruvate may convert to ethanol or lactate.