Lewis/Life - Review of Key Concepts

Review of Key Concepts - Chapter 7

The respiratory system provides the oxygen that cellular respiration requires as a final electron acceptor. The overall reaction for cellular respiration is: C6H12O6+ 6O2{2mrar}6CO2+ 6H2O+ ATP.
All cells begin energy release from nutrients with glycolysis and then may follow any of several pathways.
Cellular (aerobic) respiration harvests energy gradually. Acetyl CoA formation, the Krebs cycle, and the respiratory chain follow glycolysis. Glycolysis takes place in the cytoplasm; acetyl CoA formation, the Krebs cycle, and the respiratory chain occur in mitochondria.
ATP synthesis occurs by substrate-level phosphorylation (phosphate transfer between organic compounds) or by oxidative phosphorylation (passage of electrons along carrier molecules through oxidation-reduction reactions, setting up a proton gradient that powers phosphorylation of ADP to ATP).
In the first half of glycolysis, glucose breaks down into two molecules of the three-carbon compound PGAL. In the second half of glycolysis, the PGALs are oxidized as NAD{pos}s are reduced to NADHs, contribute phosphate groups to form two ATPs, and react and are rearranged to form two molecules of pyruvic acid.
In the mitochondria, pyruvic acid is converted into acetyl CoA in a coupled reaction that also reduces NAD{pos} to NADH.
Acetyl CoA enters the Krebs cycle. This cycle is a series of oxidation-reduction reactions that produces ATP, NADH, FADH2, and CO2. Substrate-level phosphorylation produces ATP in the Krebs cycle.
Energy-rich electrons from NADH and FADH2 fuel the respiratory chain. Electrons move through a series of carriers that release energy at each step. The terminal electron acceptor, oxygen, is reduced to form water.
Electron transport energy establishes a proton gradient that pumps protons from the mitochondrial matrix into the intermembrane compartment. As protons diffuse back into the matrix through channels in ATP synthase, their energy drives phosphorylation of ADP to ATP.
Adding the ATPs produced in substrate-level phosphorylation and oxidative phosphorylation and subtracting those used to enter the mitochondrion predicts a theoretical maximum energy of 36 ATPs per glucose.
Negative feedback coordinates the rates of glycolysis, acetyl CoA formation, and the Krebs cycle.
In the absence of oxygen, alcoholic, lactic acid, or other fermentation pathways may run. Fermentation does not produce ATP but oxidizes NADH to NAD{pos}, which is recycled to glycolysis. Alcoholic fermentation reduces pyruvic acid to ethanol and loses carbon dioxide. Lactic acid fermentation reduces pyruvic acid to lactic acid.
Anaerobic electron transport uses inorganic electron carriers and is less efficient than aerobic respiration but more so than fermentation.
Amino acids enter the energy pathways as pyruvic acid, acetyl CoA, or an intermediate of the Krebs cycle. Fatty acids and glycerol enter as acetyl CoA.