1. GLYCOLYSIS

3. www.lowcarbluxury.com/newsletter/lclnewsvol03... General features of Glycolysis 1.Anaerobic degradation of hexose sugar 2.Conversion of a 6-carbon molecule (glucose, fructose) to a 3-carbon molecule ( dihydroxyacetone phosphate, glyceraldehyde 3- phosphate; pyruvate 3.One 6-carbon molecule will give two 3-carbon molecules 4.All the intermediates are phosphorylated; -vely charged at pH 7 5.Pi bonded by either an ester or anhydride bond 6.2 phases: activation phase and energy production phase

4. 1.10 steps in glycolysis 2.First 5 steps is the preparation or activation of glucose 3.Uses 2 molecules of ATP 4.6-carbon degraded to 2 3-carbon molecules

5. 1.Step 1: Phosphorylation. Glucose converted to glucose 6 phosphate 1.Coupling reaction Glucose Glucose 6-P  G°’ = 13.8kJ/mol (3.3kcal/mol) ATP + H 2 O ADP + Pi  G°’ = -30.5kJ/mol (-7.3kcal/mol) Glucose + ATP Glucose 6-P +ADP  G°’ = -16.7kJ/mol (-4.0kcal/mol) 2. Reaction catalysed by hexokinase (remember kinase – ATP dependent enzyme 3.Substrate can be any hexose sugar (fructose, mannose, glucose) 4.Glucose 6-P inhibits hexokinase 5.Keq for this reaction is high (2000)  rxn is reversible but this does not happen in the cell b’coz: a. Hexokinase affinity for glucose and ATP is higher than for ADP and G 6-P.  hexokinase tends to be saturated with glucose and ATP b. Hexokinase is inhibited by G 6-P

6. Hexokinase is an allosteric enzyme: Activator: ADP Inhibitor: ATP and Glucose 6-Phosphate

7. Liver glucokinase requires a higher glucose concentration to achieve saturation Glucokinase: lowers blood glucose GlucokinaseHexokinase High activity in the liver Low activity in the liver Not found in muscleFound in the muscle Specific for glucoseHexoses are substrates Km(glucose) = 10mMKm(glucose) = 0.1

8. Step 2: Isomerization. Glucose 6 phosphate to fructose 6-phosphate Glucose 6-P Fructose 6-P  G°’ = 1.67kJ/mol (0.4kcal/mol) 1.The enzyme that catalyses the reaction is glucose phosphate isomerase 2.Acid-base catalysis: Lys and His in the active site: Lys acts as the acid and His as the base

10. (-3.4 kcal/mol) 1.Endergonic reaction of phosphorylation of fructose 6-P is coupled with the hydrolysis of ATP. 2 nd ATP; 2 nd activation step 2.This is the step which commits glucose to glycolysis (G 6-P and F 6-P involved in other pathways. The only way for F 1,6 bisP to be metabolised is via glycolysis 3.Highly exergonic & irreversible 4.PFK – key regulatory enzyme in glycolysis; ALLOSTERIC ENZYME 5.ATP: negative modulator Step 3: Phosphorylation of fructose 6-phosphate to Fructose 1,6bisphosphate

11. www.rpi.edu/.../MBWeb/mb1/part2/gluconeo.htm

12. (5.7 kcal/mol) 1.The last of the activations step 2.Cleavage takes place between carbon-3 and carbon-4 3.Rxn moves towards triose sugar formation although ΔG°’ is positive Step 4: Cleavage of Fructose 1,6bisphosphate to glyceraldehyde 3-P & dihydroxyacetone phosphate

13. 1.Amino acids participating in the active site: Lys, Cys (thiol grp acts as a base) and His 2.Aldol cleavage

14. ( 1.8kcal/mol) 1.2 nd glyceraldehyde 3-phosphate formed from this rxn 2.ΔG under physiological conditions is slightly positive: 2.41kJ/mol or 0.58kcal/mol 3.Reaction favours formation of glyeraldehyde 3-phosphate because  G for subsequent reactions in glycolysis are very negative and  drives the rxn forward. (Overall ΔG for glycolysis is negative) Step 5: Isomerization of Dihydroxyacetone phosphate to glyceraldehyde 3-P

15. courses.cm.utexas.edu/.../Lecture-Ch14-1.html glucose C1 and C6 becomes glyceraldehyde 3-phosphate C3 glucose C2 and C5 becomes glyceraldehyde 3-phosphate C2 glucose C3 and C4 becomes glyceraldehyde 3-phosphate C1

16. 2 nd phase of glycolysis: production of energy 1.Involves 5 steps 2.Production of ATP

17. (1.5kcal/mol) 1.Involves 2 sets of reactions: i) Electron transfer rxn, from Glyceraldehyde 3-P to NAD + ii) The addition of a phosphate 2. G 3-P to 3-Phosphoglycerate ΔG°’= -43.1kJ/mol (-10.3kcal/mol) (oxdn) 3-PG to 1,3 bisPG ΔG°’ = 49.3kJ/mol ( 11.8kcal/mol) (phosln) Overall ΔG°’= 6.2kJ/mol (1.5kcal/mol) Step 6: Oxidation of Glyceraldehyde 3-P to 1,3 bisphosphoglycerate

18. Oxidation of glyceraldehyde 3- phosphate to a carboxylic acid EXERGONIC 1 2 3 Electron transfer from G3-P to NAD+ 3-phophoglycerate ENDERGONIC

19. Step 7: Conversion of 1,3 bisphosphoglycerate to 3-phosphoglycerate (-4.5kcal/mol) 1.A phosphate grp is transferred frm 1,3bPG to ADP 2.First ATP formed in glycolysis 3.Substrate-level phosphorylation Question: If the ΔG°’for the hydrolysis of 1,3bPG = -49.3kJ/mol and the ΔG°’the hydrolysis of ATP is – 30.5kJ/mol, what is the ΔG°’for the formation of 3-phosphoglycerate and ATP?

20. Step 8: Conversion of 3-PG to 2-PG (1.1 kcal/mol) Step 9: Dehydration of 2-PG to phosphoenolpyruvate (PEP) (0.4 kcal/mol)

21. Step 10: Transfer of phosphate grp. from phosphoenolpyruvate (PEP) to ADP (-7.5 kcal/mol) 1.PEP high energy compd. with high phosphate-grp transfer potential 2.Another example of substrate level phosphorylation 3.Pyruvate kinase is an allosteric enzyme 4.Pyruvate kinase is inhibited by high levels of ATP

22. Conversion of pyruvate to lactate in the muscle 1.Rxn is catalysed by lactate dehydrogenase 2.NAD + is the co-factor 3.Rxn highly exergonic: ΔG°’=25.1kJ/mol (6kcal/mol) 4.Lactate can be recycled in the liver to form pyruvate and glucose by gluconeogenesis

24. www.biologie.uni-hamburg.de/b-online/e19/19d.htm

25. Overall conversion of glucose to 2 moles of pyruvate: ΔG°’= -73.3 kJ/mol (-17.5kcal/mol)

26. www.nd.edu/~aseriann/glyreg.html Regulation of glycolysis 1.Hexokinase 2.Phosphofructokinase 3.Pyruvate kinase

27. www-medlib.med.utah.edu/NetBiochem/tabletit.htm

28. SubstrateToATP GlucoseGlucose 6-phosphate Fructose 6-phosphateFructose 1,6 bisphosphate 2 x 1,3 phophoglycerate2 x 3-phosphoglycerate+2 2 x PEP2 x pyruvate+2 Net2

29. ATP production and Efficiency of Glycolysis Glucose + 2 ADP + 2P i 2 Lactate + 2 ATP  G  ’ = -184.5kJ/mol(-44.1 kcal/mol) But in glycolysis only 2 ATPs are formed when glucose is oxidised to lactate. To form the ATP molecules would require : 161.1kJ/mol(-14.6 kcal/mol) 2ADP + 2Pi 2ATP ΔG°’= 61.1kJ/mol(-14.6 kcal/mol) % of energy conserved is 61.1/184.5 x 100 = 33.1%

30. Conversion of pyruvate to lactate in the muscle 1.Rxn is catalysed by lactate dehydrogenase 2.NAD + is the co-factor 3.Rxn highly exergonic: ΔG°’=25.1kJ/mol (6kcal/mol) 4.Lactate can be recycled in the liver to form pyruvate and glucose by gluconeogenesis

31. Conversion of lactate to glucose in the liver: anaerobic conditions