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Unformatted text preview: Glycolysis: The Initial Steps: Energy Input – 9.1.1 Glycolysis: The Energy Payoff – 9.1.2 I. The redox “fall” of electrons in cellular respiration is stepwise and uses (NAD+) Nicotinamide adenine dinucleotide • Gains an electron therefore reduction; it picks up 2 electrons to an electron transport • Electrons removed from glucose during cellular respiration are not transferred directly to oxygen, but are first passed to a special electron receptor NAD + A. NAD+ (see fig. 9.4) B. Coenzyme R R | dehydrogenase | H-C-OH + NAD+ ============> C=O + NADH + H+ | | R’ R’ • NAD + is reduced to NADH, and CHRR’OH is oxidized to CRR’O • NAD + has only slightly greater affinity for electrons than other organic molecules. • The electrons that are transferred to NAD+ are then transferred into the electron transport chain C. Electron transport chain (see fig 9.5) II. Cellular respiration is a cumulative function of glycolysis, the Krebs cycle, and electron transport. A. Three metabolic stages of cellular respiration (see fig 9.6) 1. Glycolysis – splits the sugars 2. Krebs cycle 3. Electron transport chain and oxidative phosphorylation III. Glycolysis harvests chemical energy by oxidizing glucose to pyruvate A. Glycolysis 1. A multi-step pathway that takes place in the cytoplasm. 2. Partially oxidizes (break down) of glucose (C6) in two pyruvate (C3) molecules. 3. Occurs with or without O2 a. This is where it is determined to be cellular respiration or fermentation B. The reactions of glycolysis occur in two phases (see fig. 9.8) 1. Energy-investment phase a. Uses cellular ATP to phosphorylate glycolysis intermediates b. Costs two ATP molecules per glucose c. Glucose can cross almost every membrane, we want glucose to stay in the cytoplasm we have to convert it to something else so it doesn’t leave To trap glucose in cytoplasm Glucose has a lot of energy in it, but we want to energize it even more When glucose is spit in half, the halves have to look alike - identical d. 2 ATP makes glucose symmetrical and into a fructose 2. Energy-yielding phase a. Produces ATP by substrate-level phosphorylation b. Yields 4 ATP molecules per glucose c. Reduces 2 molecules of NAD+ to NADH per glucose (net ATP – 2) C. A small amount of ATP generated by substrate-level phosphorylation (see fig. 9.7) 1. Substrate-level phosphorylation – ATP production by direct enzymatic transfer of phosphate from an intermediate substrate in catabolism to ATP *The summary equation for glycolysis (see fig. 9.8) C 6 H 12 O 6 + 2 NAD + + 2 ADP + 2 P i => 2 C 3 H 4 O 3 + 2 NADH + 2 H + + 2 ATP + 2 H 2 O Spit glucose into 2 • We get 2 pyruvates, 2 energized electrons, 2 hydrogens, 2 ATP, and water *Glycolysis leads either to the Krebs cycle or fermentation (If oxygen is present we can do cellular respiration; if oxygen is NOT present we do fermentation – Krebs cycle) IV. The Krebs cycle completes the energy-yielding oxidation of organic molecules. It takes the pyruvate and completely tears IV....
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This note was uploaded on 03/19/2010 for the course BIOL 1201 taught by Professor Wishtichusen during the Fall '07 term at LSU.
- Fall '07