9-24-08_kinetics2A0

9-24-08_kinetics2A0 - Enzymes are things invented by...

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Enzymes are things invented by biologists that explain things which otherwise require harder thinking” –Jerome Lettvin Pinky : Egad. You astound me, Brain. Brain : That's a simple task, Pinky. http://programs.northlandcollege.edu/biology /Biology1111/animations/enzyme.html
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Intial phosphorylation of glucose uses ATP You have to spend money to make money! ATP hydrolysis coupled with phosphorylation of glucose is energetically favorable
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A second ATP adds a second phosphate to the sugar (now fructose) Fructose bisphosphate (6 carbons) is broken down into two three carbon glyceraldehyde-3-phosphate Even though ΔG°’ > 0 for steps 4 and 5, the concentrations of the molecules make this ΔG near 0 (equilibrium)
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Acidification of glyceraldehyde3-phosphate results in the formation of NADH, H+ and one ATP n icotinamide a denine d inucleotide (NAD) plays a key metabolic role First reaction is oxidation-reduction; 2 electrons & proton (equal to a hydride ion; :H-) are transferred from glyceraldehyde-3-phosphate (oxidized) to NAD+ (reduced) forming NADH NADH and its role in the electron transport chain and ATP formation will be discussed later in the course
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Removal of phosphate from PEP to form pyruvate makes another ATP Even though ΔG°’ for making ATP in step 7 is -4.5 kcal/mol, ΔG is near 0 during glycolysis (Recall that high [ATP] is maintained)
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Key points of glycolysis Two ATPs are used to drive two initial phosphorylation reactions, which would be energetically unfavorable by themselves Non-favorable steps are near equilibrium mainly through maintenance of appropriate reactant and product concentrations A 6 carbon molecule (fructose 1,6 bisphosphate) is broken down into two three carbon molecules (glyceraldehyde-3-phosphate) Addition of a second phosphate to the three carbon molecule requires phosphate (Pi) and reduces NAD+ (NAD+ → NADH + H+) Each 1,3 bisphosphoglycerate donates a phosphate to make 1 ATP Reconfiguration makes phosphoenolpyruvate, which is converted to pyruvate in an energetically favorable reaction that also creates 1 ATP Net equation: Glucose + 2ADP + 2Pi + 2 NAD+ → 2 pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O NAD+ must be regenerated for glycolysis to continue for long periods
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9-24-08_kinetics2A0 - Enzymes are things invented by...

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