All living organisms need energy to function and we get this energy from the foods we eat. The most efficient way for cells to harvest energy stored in food is through cellular respiration. Cellular respiration is defined as the aerobic harvesting of chemical energy from organic fuel molecules. Cellular respiration occurs in eukaryotic and prokaryotic cells. It has three main stages: glycolysis, the citric acid cycle, and electron transport. Stage one glycolysis means the “splitting of sugar”. Glycolysis is a six carbon glucose molecule which is then broken in half, forming two three carbon molecules. The initial split requires an energy investment of two ATP molecules per glucose. Then the three carbon molecules donate high energy electrons to NAD+, the electron carrier forming NADH. Glycolysis then makes four ATP molecules when the enzymes transfer phosphate groups from fuel molecules to ADP. Glycolysis produces a net of two molecules of ATP per molecule of glucose. Then the pyruvic acid holds most of the energy of glucose and that energy is then harvested for stage two. Stage two the citric acid cycle. The two molecules of pyruvic acid that fuel the remains after glycolysis are not ready yet. The pyruvic acid must be converted to a form the citric acid cycle can use. First each pyruvic acid loses a carbon as CO2. The remaining fuel molecules each with 2 carbons left are called acetic. The oxidation of the fuel generates NADH. Lastly each acetic acid is attached to a molecule called coenzyme A (CoA), an enzyme from the formed from the B vitamin pantothenic acid to form acetyl CoA. The CoA escorts the acetic acid into the first reaction of the citric acid cycle. The CoA is then stripped and recycled. The third stage is electron transport. The molecules of electron transport chains are built into the inner membranes of mitochondria. It is the NADH and FADH...
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