Lect14_ferment

Lect14_ferment - Harvesting energy Without an external...

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1 Day 14 Glycolysis and Fermentation Harvesting energy Without an external electron acceptor Today’s Topics 1. Glycolysis: An example of a redox reaction that powers cells 2. Fermentation: recycling NADH back to NAD+ in the absence of an external electron acceptor 3. Using ATP in biosynthesis All life is about Obtaining electrons from some donor, Transferring the electrons to an acceptor And exploiting the released energy. 1) Where to get electrons? That is, what to use as a donor 2) What to do with the electrons afterwards? Or, what to use as an acceptor Life has found many solutions. Since all forms of life are run by REDOX chemistry, two problems must be solved in some way : 1. The donor is some organic molecule or “food” ( heterotrophs like you and me) 2. The ultimate acceptor comes from inside the cell ( fermenters ) (animal cells sometimes do this) Today we’ll talk about life forms in which: General diagram of how cells burn fuel (so far) Fuel AB C D E F 2e - , 2H + 2e - , 2H + G Release energy Release energy NADH NADH pull push By adjusting c oncentrations via highly exergonic Redox Reaction
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2 General diagram of how cells burn fuel (so far) Fuel AB C D E F 2e - , 2H + 2e - , 2H + G Release energy Release energy NADH NADH pull push Reactions further away can be influenced using ATP Fuel CD E F 2e - , 2H + pull push G ATP production coupled (or pushed) by Redox ATP ADP 2e - , 2H + NADH NADH Fuel E F 2e - , 2H + pull push 2e - , 2H + G ATP ADP ATP ADP The hydrolysis of ATP pushes an unfavorable reaction Redox pushes ATP production NADH NADH Fuel E F 2e - , 2H + pull push 2e - , 2H + G ATP ADP ATP ADP Each oxidative pathway manages its own affairs and … makes an excess of ATP and reducing power (e - , H + ) NADH NADH An example of redox. Glycolysis: Using sugar as fuel • Glycolysis – Oxidation of glucose – “Sugar-splitting” of one 6C sugar into two 3C sugars – NADH and ATP are formed in the process – Cells can make a living this way – Virtually all cells have the capability to run this pathway – Partial oxidation of glucose Glycolysis, cont. • 10 steps (10 enzymes) • First 5 steps are endergonic – Necessary to de-stabilize glucose – Involves phosphorylation of glucose • Next 5 steps are exergonic – Redox, electrons transferred to NAD – Phosphorylation of ADP (substrate-linked phosphorylation) to produce ATP
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3 Figure 7.7 Changes in Free Energy During Glycolysis - 2 e - + 2H + 1 Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate H H H H H OH OH HO OH CH2O H H H H O H OH HO
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Lect14_ferment - Harvesting energy Without an external...

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