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Refer to chapter 16, Stryer, 5e & chapter 14, Lehninger, 5e

The biosynthesis of cell constituents III: glycolysis: steps 6-10. Refer to chapter 16, Stryer, 5e & chapter 14, Lehninger, 5e. Lecture 18, Michael Schweizer. steps 6-10. Glycolysis continued. Recall that there are 2 GAP per glucose. 6. Glyceraldehyde-3-phosphate dehydrogenase catalyzes:

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Refer to chapter 16, Stryer, 5e & chapter 14, Lehninger, 5e

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  1. The biosynthesis of cell constituents III: glycolysis: steps 6-10 Refer to chapter 16, Stryer, 5e & chapter 14, Lehninger, 5e Lecture 18, Michael Schweizer

  2. steps 6-10 Glycolysis continued. Recall that there are 2 GAP per glucose.

  3. 6. Glyceraldehyde-3-phosphate dehydrogenase catalyzes: glyceraldehyde-3-P + NAD+ + Pi 1,3-bisphosphoglycerate + NADH + H+

  4. GAP + H2O + NAD+ 3-PGA DGo’ = -12 kcal . mol-1 3-PGA + Pi 1,3-bisPGA DGo’ = + 12 kcal . mol-1 (1,3-bisPGA + H2O 3-PGA + PiDGo’ = -11.8 kcal . mol-1) Participation of a common intermediate: 1,3-bis-PGA GAP + NAD+ + Pi 1,3-bisPGA + NADH+H+DGo’ = +1.5 kcal . mol-1 (step 6) 1,3-bisPGA + ADP 3-PG + ATP DGo’ = -4.5 kcal . mol-1 (step 7) Sum of the two reactions: 3-GAP + NAD+ + Pi+ ADP 3-PGA + NADH+ + H+ + ATP DGo’ = -3 kcal . mol-1

  5. The aldehyde of glyceraldehyde-3-phosphate reacts with the cysteine thiol to form a thiohemiacetal. Oxidation to a carboxylic acid (in a ~ thioester) occurs, as NAD+ is reduced to NADH. The “high energy” acyl thioester is attacked by Pi to yield the acyl phosphate (~P) product.

  6. Glycolysis Step 6 Oxydation of an aldehyde to a carboxylic group, releases sufficient DG to drive NAD+ to NADH + H+ and creates a (~P) high “energy” bond (“mixed” anhydride) Oxidation of GAP yields substantial energy: “investment of (2~P) at steps 1 & 3 can be returned with profit at steps 7 & 10. 1,3-bisphosphoglycerate (1,3-bisPG) DGo’ = -11.8 kcal . mol--1

  7. Glycolysis Step 7 First substrate level phophorylation (energy from oxydation of step 6)

  8. steps 8-10 Refer to chapter 16, Stryer, 5e & chapter 14, Lehninger, 5e

  9. 8. Phosphoglycerate Mutase catalyzes: 3-phosphoglycerate2-phosphoglycerate Phosphate is shifted from the OH on C3 to the OH on C2. An active site His participates in phosphate transfer. The process involves a 2,3-bisphosphateintermediate Reposition of (~P) from C-atom No.3 to C-atom No.2.

  10. 9. Enolase catalyzes 2-phosphoglyceratephosphoenolpyruvate+H2O This Mg++-dependent dehydration reaction is inhibited by fluoride. Fluorophosphate forms a complex with Mg++ at the active site (creating by dehydration an energy-rich enolic phosphate, DGo’ = -14.8 kcal . mol-1).

  11. 10. Pyruvate Kinase catalyzes: phosphoenolpyruvate + ADPpyruvate+ATP This reaction is spontaneous. PEP has a larger DG of phosphate hydrolysis than ATP. Removal of Pi from PEP yields an unstable enol, which spontaneously converts to the keto form of pyruvate. (DGo’ = (-6.8 (enolpyruvate) + -8.0 kcal. mol-1 (tautomerisation)) = -14.8 kcal . mol-1); One would expect that the DGo’ for this reaction would be -7,5 kcal. mol-1, but it is -6.1 kcal. mol-1, but the equilibrium and therefore DGo’ are so far to the right that it is difficult to obtain an accurate value for K’eq and DGo’).

  12. Glycolysis Step 10 Second substrate level phosphorylation PEP is a “high energy” phosphate-containing molecule: the product pyruvate can isomerize (pyruvate is capable of allowing electron delocalisation: enhanced resonance stabilisation and tautomerization of product molecules) Pyruvate – end product of glycolysis

  13. Glycolysis Glycolysis is the breakdown of glucose into pyruvate. This process requires ADP and NAD+ as co-factors. A cell can always find a way to hydrolyse ATP back into ADP, but NAD+ is more difficult as its formation involves oxydation of NADH. Under anaerobic conditions another electron acceptor is needed, under aerobic conditions the electrons from NADH can ultimately passed onto O2.

  14. Refer to chapter 16, Stryer, 5e

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