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Cellular Respiration

•	the waste products of respiration, carbo dioxide and water, are the raw materials for photosynthesis •	fermentation is partial degradation of sugars that occurs without the use of oxygen; the most prevalent and efficient catabolic pathway is cellular respiration, in which oxygen is consumed as a reactant along with the organic fuel The Principle of Redox: •	transfer of one or more electrons from one reactant to another; these electron transfers are called oxidation-reduction reactions, or redox reactions for short •	in redox reaction, the loss of electrons from one substance is called oxidation, and the addition of electrons to another substance is known as reduction •	the electron donor is called the reducing agent; the electron acceptor, is the oxidizing agent •	a redox reaction that relocates electrons closer to oxygen, such as the burning of methane, releases chemical energy that can be put to work

•	the hydrogen atoms are not transferred directly to oxygen, but instead are usually passed first to a coenzyme called NAD+ •	as an electron acceptor, NAD+ functions as an oxidizing agent during respiration •	enzymes called dehydrogenases remove a pair of hydrogen atoms (two electrons and two protons) from the substrate (a sugar, for example), thereby oxidizing it; the enzyme ddelivers the two electrons along with one proton to its coenzyme, NAD+; the other proton is released as a hydrogen ion into the surrounding solution •	by retrieving two negatively charged electrons but only one positively charged proton, NAD+ has its charge neutralized when it is reduced to NADH •	each NADH molecule formed during respiration represents stored energy that can be tapped to make ATP when the electrons complete their “fall” down an energy gradient from NADH to oxygen •	during cellular respiration, most electrons travel the following “downhill” route: food NADH electron transport chain oxygen •	first two stages of cellular respiration, glycolysis and the citric acid cycle, are the catabolic pathways that compose glucose and other organic fuels •	glycolysis that occurs in the cytosol, begins the degradation process by breaking glucose into two molecules of a compound called pyruvate •	the cytric acid cycle that takes place within the mitochondrial matrix, completes the breakdown of glucose by oxidizing a derivate of pyruvate to carbon dioxide •	in the third stage of respiration, the electron transport chain accepts electrons from the breakdown products of the first two stages (most often via NADH) and passes these electrons from one molecule to another; at the end of the chain, the electrons are combined with molecular exygen and hydrogen ions, forming water; this mode of ATP synthesis is called oxidative phospohorylation because it is powered by the redox reactions of the electron transport chain •	the inner membrane of the mitochondrion is the site of electron transport and chemiosmosis, the process that together constitute oxidative phospohorylation •	for each molecule of glucose degraded to carbon dioxide and water by respiration, the cell makes up to about 38 molecules of ATP

humbertin