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GLYCOLYSIS

GLYCOLYSIS. O 2 absent. O 2 present. Glycolysis can be divided into two phases: priming and payoff. Phase 1: five priming reactions 1. glucose + ATP G-6-P + ADP 2. G-6-P F-6-P 3. F-6-P + ATP F-1,6-bisP + ADP 4. F-1,6,bisP DHAP + G-3-P

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GLYCOLYSIS

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  1. GLYCOLYSIS

  2. O2 absent O2 present

  3. Glycolysis can be divided into two phases: priming and payoff Phase 1: five priming reactions 1. glucose + ATP G-6-P + ADP 2. G-6-P F-6-P 3. F-6-P + ATP F-1,6-bisP + ADP 4. F-1,6,bisP DHAP + G-3-P 5. DHAP G-3-P

  4. Glycolysis can be divided into two phases: priming and payoff • Phase 2: five payoff reactions • 6. G-3-P + PI + NAD+ • 1,3-bisPGA + NADH • 7. 1,3-bisPGA + ADP • 3-PGA + ATP 8. 3-PGA 2-PGA 9. 2-PGA PEP • PEP + ADP pyruvate + ATP

  5. Reaction 6 DGo’ =+6.3 kJ/mol DG’ = -1.29 kJ/mol Near equilibrium: not regulated Note that the C in -C-O-PO3 has been oxidized (from aldehyde to acid)

  6. The coupling of acyl-phosphate formation to oxidation avoids an energy hump that would drastically slow the reaction.

  7. including oxidation of NADH

  8. In fungi and plants in the absence of O2, pyruvate is decarboxylated to acetaldehyde; acetaldehyde is reduced to ethanol; NADH is oxidized to NAD+. The NAD+ is recycled to oxidize more glyceraldehyde-3-P.

  9. In animals and some bacteria, pyruvate is reduced to lactate as NADH is oxidized to NAD+.

  10. Control: activity of glycolysis depends on allosteric enzymes and responds to energy requirement. In muscle:

  11. Control: activity of glycolysis depends on allosteric enzymes and responds to energy requirement. In liver, fructose-2,6-bisP is a important stimulator of PFK: enhances substrate activation relieves allosteric inhibition

  12. Summary • Glucose is metabolized to pyruvate in a series of 10 reactions. • Glycolysis provides the cell (cytoplasm) with 2 mol ATP/glucose. • Glycolysis also provides cytoplasm with 2 mol NADH/glucose. • In the absence of O2, NADH is oxidized by reduction of pyruvate. • In the presence of O2, NADH is oxidized in the mitochondria. • Rate of glycolysis is controlled at 3 key allosteric enzymes.

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