Chapter 18

Chapter 18 - Chapter 18 Glycolysis o Phase 1 Steps (G = ~50...

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Chapter 18 Glycolysis o Phase 1 Steps (ΔG = ~50 kJ/mol) 1. glucose + ATP + Hexokinase/Glucokinase glu-6-P + ADP 1 st priming rxn (b/c of ATP) forward rxn favored (large -ΔG) b/c [glu-6-P] and [ADP] are about 100Xs lower than [glucose] and [ATP], respectively (irreversible) neg. charge on glu-6-P traps it in cell (can’t pass plasma membrane) rapid phosphorylation keeps cellular [glucose] low, favoring diffusion of glucose into cell hexokinase has a low K m for glucose (aka affinity for glucose is high) glucokinase has higher K m for glucose than hexokinase (aka less affinity for glucose than hexokinase has) ↑ [glucose] ↑ insulin + glucose uptake, + glycolysis,+ glycogen synthesis by switching on glucokinase), - glycogen breakdown, - gluconeogenesis 2. glu-6-P + Phosphoglucoisomerase fruct-6-P isomerization of aldose (pyranose) to ketose (furanose) (carbonyl O shifted from C1 to C2) makes C1 more reactive for step 3; activates C3 for cleavage in step 4 3. fruct-6-P + ATP + Phosphofructokinase (aka PFK) fruct-1,6- bisP + ADP 2 nd priming rxn irreversible; commits cell to metabolizing glycolysis instead of storing it ATP is both substrate and allosteric inhibitor for PFK; at high [ATP], K m of PFK increases (rxn becomes more cooperative) ↓ [ATP] and [citrate] and ↑[AMP] and [fruct.-2,6-bisP] = + glycolysis o 2 ADP + Adenyl Kinase ATP + AMP feed-forward loop
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o ↑ [glucose] ↑ [fruct-6-P] + PFK-2 ↑ [fruct-2,6-bisP] + PFK-1 ↑ [fruct-1,6-bisP] 4. fruct-1,6-bisP + Fructose Bisphosphate Aldolase dihydroxyacetone P (aka DHAP) + glyceraldehyde-3-P (aka G-3- P) cleavage of C3-C4 bond 5. DHAP + Triose Phosphate Isomerase G-3-P reversible rxn, but G-3-P enters Phase 2 directly, so rxn is
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Chapter 18 - Chapter 18 Glycolysis o Phase 1 Steps (G = ~50...

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