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Download Ch 9: E.T.C./ Oxidative Phosphorylation
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Ch 9 (Part 3): E.T.C./ Oxidative Phosphorylation • So far, in glycolysis & the Krebs cycle, 1 glucose molecule has resulted in: – 4 ATPs (2 from glycolysis, 2 from Krebs) – 10 NADH (2 from gly., 2 from acetyl-CoA step, 6 from Krebs Cycle) – 2 FADH2 (from Krebs Cycle) ELECTRON TRANSPORT CHAIN (E.T.C.) • a collection of molecules embedded in the inner membrane of mitochondrion (folding of inner membrane to form cristae) • the groups along the chain alternate between reduced & oxidized states as they accept and donate electrons • each successive group is more electronegative than the group before it, so the electrons are “pulled downhill” towards OXYGEN (the final electron carrier!) • as molecular oxygen (O2) is reduced, it also picks up H+ from the environment to form water (H2O) ATP Production of the E.T.C. Typically, the ATP produced is as follows: 1 NADH 3 ATP 1 FADH2 2 ATP (“exchange rate”) (FADH2 is “dropped off” at a lower point in the E.T.C., so it generates fewer ATPs) • The E.T.C. does not make ATP directly – it generates a proton gradient across the mitochondrial membrane, which stores potential energy that can be used to phosphorylate ADP • Some of the proteins in the e.t.c. pump H+ against their gradient…this generates a proton (H+) gradient called the PROTON MOTIVE FORCE. (outer matrix) -protons then diffuse back across the membrane through the ATP synthase complex which causes the phosphorylation of ADP to form ATP! H+ H+ H+ H+ H+ ADP + Pi ATP (inner matrix) CHEMIOSMOSIS: • the coupling of exergonic electron flow down an E.T.C. to endergonic ATP production; the proton gradient drives ATP synthesis as protons diffuse back across the membrane **accomplished by ATP synthase complex! We Have an Animation!! SUMMARY: • most ENERGY flows in this sequence: Glucose NADH e.t.c. proton ATP motive force PROCESS Glycolysis ATP produced by subs. Phos. 2 ATP ox. of pyruvate to acetyl CoA (LINK) Krebs cycle 2 ATP Reduced coenz. 2 NADH ATP produced by oxid. phos. (in the E.T.C.) TOTAL 4-6 ATP 6-8 2 NADH 6 ATP 6 6 NADH 2 FADH2 18 ATP 4 ATP 24 TOTAL 36-38! Energy in organic compd. NADH/FADH2 ETC (oxidative phosphorylation) • approximately 40% of energy in glucose is converted to ATP • the remaining energy is lost as heat Alternative Metabolic Pathways - Vocabulary: • aerobic: existing in presence of oxygen • anaerobic: existing in absence of oxygen • fermentation = anaerobic catabolism of organic nutrients Alcoholic Fermentation Pyruvate + NADH ethanol + CO2 + NAD+ • pyruvate is converted to ethanol • NADH is oxidized to NAD+ (recycled) • performed by yeast and some bacteria Lactic Acid Fermentation Pyruvate + NADH lactic acid + NAD+ • pyruvate is reduced to lactic acid • NADH is oxidized to NAD+ (recycling of NAD+) • performed by some bacteria (producing cheese and yogurt) • performed by our muscle cells when oxygen is scarce Fermentation differs from cellular respiration in: • method NADH is recycled back to NAD+ • in fermentation, the final electron acceptor is pyruvate, not O2 • amount of total energy harvested (2 ATP from glycolysis instead of 36-38 using Kreb’s and ETC) EXTRA VOCABULARY: E. Coli • Obligate anaerobes: only grow in absence of oxygen (e.g. Clostridium botulinum) • Obligate aerobes: only grow in presence of oxygen Micrococcus luteus • Facultative anaerobes: can grow in either presence or absence of oxygen (e.g. yeast; bacteria that make yogurt, cheese; our muscle cells at the cellular level) *pyruvate is a “fork” in the metabolic road which leads to 2 alternate catabolic routes: -if O2 is present: Krebs and e.t.c. -if no O2 is present: Fermentation