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 5. DHAP G-3-P 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 10.PEP + ADP pyruvate + ATP Reaction 6 G o =+6.3 kJ/mol G = kJ/mol Near equilibrium: not regulated Note that the C in -C-O-PO 3 has been oxidized (from aldehyde to acid) The coupling of acyl-phosphate formation to oxidation avoids an energy hump that would drastically slow the reaction. including oxidation of NADH In fungi and plants in the absence of O 2, 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. In animals and some bacteria, pyruvate is reduced to lactate as NADH is oxidized to NAD +. Control: activity of glycolysis depends on allosteric enzymes and responds to energy requirement. In muscle: 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 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 O 2, NADH is oxidized by reduction of pyruvate. In the presence of O 2, NADH is oxidized in the mitochondria. Rate of glycolysis is controlled at 3 key allosteric enzymes.