D. Cellular Respiration
1. Aerobic Respiration
Learning Objectives for this Section
Cellular respiration (def) is the process cells use to convert the energy in the chemical bonds of nutrients to ATP energy. Depending on the organism, cellular respiration can be aerobic, anaerobic, or both. Aerobic (def) respiration is an exergonic pathway that requires molecular oxygen (O2). Anaerobic (def) exergonic pathways do not require oxygen and include anaerobic respiration and fermentation. We will now look at these three pathways.
Aerobic respiration (def) is the aerobic catabolism of nutrients to carbon dioxide, water, and energy, and involves an electron transport system (def) in which molecular oxygen is the final electron acceptor. Most eukaryotes and prokaryotes use aerobic respiration to obtain energy from glucose. The overall reaction is:
C6H12O6 + 6O2 yields 6CO2 + 6H2O + energy (as ATP)
This type of ATP production is seen in aerobes and facultative anaerobes. Aerobes are organisms that require molecular oxygen because they produce ATP only by aerobic respiration. Facultative anaerobes, on the other hand are capable of aerobic respiration but can switch to fermentation, an anaerobic ATP-producing process, if oxygen is unavailable.
Aerobic respiration involves four stages: glycolysis, a transition reaction that forms acetyl coenzyme A, the citric acid (Krebs) cycle, and an electron transport chain and chemiosmosis. We will now look at each of these stages.
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