Glycolysis

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Glycolysis

Transcript of Glycolysis

  • 1. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 1

2. BiochemistryGlycolysis andGluconeogenesisBy Muhammad Ramzan Ul RehmanMUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 2 3. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 3 4. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 4 5. Overview ofcarbohydratemetabolismMUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 5 6. GLYCOLYSIS Glycolysis occurs in almost every living cell. It occurs in cytosol. It was the first metabolic sequence to be studied. Most of the work done in 1930s by the German biochemist G.Embden Meyerhof Warburg. That is why it is also called Embden-Meyerhof pathway. It is a Greek word. Glykos sweet Lysis loosing Glycolysis loosing or splitting of glucoseMUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 6 7. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 7 8. Glycolysis Glc is an important fuel for most organisms. Why is Glc chosen? Glc is one of the monosaccarides formed formaldehydeunder prebiotic conditions. Glc has a low tendency to glycosylate proteins Fermentations provide usable energy in the absence ofoxygen Why is a relatively inefficient metabolic pathway soextensively used? Answer: It does not require oxygen Obligate anaerobes Facultative anaerobesMUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 8 9. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 9 10. Glycolysis 3 of the reactions of glycolysis are irreversible. Pyruvate is the end product of glycolysis in tissues withmitochondria. This series of 10 reactions, called aerobic glycolysis, sets thestage for the oxidative decarboxylation of pyruvate to AcetylCoA, major fuel of the citric acid cycle. Under anaerobic conditions, pyruvate can be reduced byNADH to form lactate. This happens when the rate of NADH formation exceeds theoxidative capacity of the cell.Glucose Lactate (anaerobic glycolysis) If there is no mitochondria (RBCs) or cells that haveinsufficient oxygen.MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 10 11. Stages of glycolysisStage I Glc is converted to fructose 1,6 bisphosphate by Phosphorylation Isomerization Second phosphorylationGoal: To trap the Glc in the cellMUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 11 12. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 12 13. IMPORTANCE OF PHOSPHARYLATED INTERMEDIATESEach of the 9 glycolytic intermediates between glucose andpyruvate is phosphorylated. The phosphate group has 3functions.1.Because the P group is ionized at pH 7 and has charge andbecause plasma membranes are not permeable to the charged mols,the phosphorylated molecules can not pass the membranes. Theyare trapped in the cell.2.P groups are necessary for chemical energy. Energy is releasedafter the hydrolysis of ATP.3.Binding of P groups to the active sites of enzymes provides bindingenergy which decreases the activation energy and increase thespecificity of enzyme-catalyzed reactions.MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 13 14. PHOSPHORYLATION OF GLUCOSEGlucose obtained from the diet through intestinal hydrolysis of lactose,sucrose, glycogen, or starch is brought into the hexose phosphate poolthrough the action of hexokinase. Free glucose phosphorylated by hexokinase (irreversible reaction 1)Hexokinase actually traps glucose in a form that does not diffuse out of thecell. Because phosphorylated sugar molecules do not readily penetrate cellmembranes without specific carriers, this commits glucose to furthermetabolism in the cell. In all tissues, the phosphorylation of glucose iscatalyzed by hexokinase, one of the three regulatory enzymes of glycolysis.MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 14 15. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 15 16. GlycolysisMUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 16 17. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 17 18. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 18 19. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 19 20. Difference between hexokinase and glucokinaseHexokinase: Its function is to make sure there is enough glc for the tissues,even in the presence of low blood glc concentrations, byphosphorylating all the glc concentration gradient between theblood and the intracellular environment.Glucokinase: Its function is to remove glc from the blood following a meal.Hexokinase, phosphofructokinase and pyruvate kinaseare 3 regulatory enzymes of glycolysis.MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 20 21. Hexokinase vs glucokinaseLiver has an additional enzyme, glucokinase, that phosphorylateonly glc1. Glucokinase has a high Km, because it phosphorylates glc onlywhen its concentration is high. This occurs during the brief periodafter consumption of a carbohydrate rich meal, when high glc aredelivered by portal vein.2. Glucokinase has a high Vmax, allowing the liver to removeeffectively this flood of glc from the portal blood. So this preventsextreme hyperglycemia after meals.MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 21 22. SUMMARYHexokinase GlucokinaseTissue dist all liverKm low highVmax low highSubstrate D-glc and other D-glc onlyInhibition by G-6-P Yes noMUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 22 23. More about HKHexokinase, like adenylate kinase and all other kinases,requires Mg (or Mn) for activity.Hexokinase is also one of the induced-fit model enzymes. It has two lobes that move towards each other when Glc is bound!Substrate-induced cleft closing is a general feature ofkinases.Other kinases (Pyruvate kinase, phosphoglycerate kinaseand PFK) also contain clefts between lobes that closewhen substrate is bound.MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 23 24. 2. ISOMERIZATION OF G-6-PThe isomerization of G-6-P (an aldose sugar) to F-6-P (a ketose sugar) is catalyzed bypgosphoglucose isomerase. The reaction is readilyreversible, is NOT a rate limiting or regulated step.MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 24 25. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 25 26. 3. PHOSPHORYLATION OF F-6-PIrreversible phosphorylation reaction catalyzed byPFK (phosphofructokinase) is the most importantcontrol point of glycolysis.Within the cell, the PFK reaction is the rate-limitingstep in the glycolytic breakdown of glc. It is controlledby the concentrations of the substrates ATP and F-6-PMUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 26 27. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 27 28. Formation of Fructose 1,6-bisphosphateMUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 28 29. 4. CLEAVAGE OF F-1,6BIPAldolase cleaves F-1,6-biP to dihydroxyacetonephosphate glyceraldehyde 3-P.The reaction is reversible is not subject toregulation.MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 29 30. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 30 31. 5. ISOMERIZATION OF DIHYDROXYACETONE-PTriose phosphate isomerase (TIM) catalyzes thereversible interconversion of dihydroxyacetonephosphate and glyceraldehyde 3-phosphate.X-ray crystallographic and other studies showed thatGlu 165 plays the role of a general acid-base catalyst.TIM has 8 parallel beta and 8 alpha helices (ab barrel).This structure is also found in Aldolase Enolase Pyruvate kinaseMUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 31 32. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 32 33. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 33 34. moreDi-OH-acetone-P can not proceed further on thedirect pathway of glycolysis and must beisomerized to glyceraldehyde-3-P for furthermetabolism in the glycolytic pathway.So, this isomerization results 2 mols ofglyceraldehyde -3-P from fructose 1,6 biP.MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 34 35. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 35 36. 6. OXIDATION OF GLYCERALDEHYDE 3-P.Because there is only a limited amount of NAD+ in the cell, the NADHformed in this reaction must be reoxidized back to NAD+ for glycolysis tocontinue. Two major mechanisms for oxidizing NADH are The NADH-linked conversion of pyruvate to lactate Oxidation by the respiratory chain.The high energy P group at carbon of 1,3-bisPG conserves much of thefree energy produced by the oxidation of Glycerate-3-PMUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 36 37. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 37 38. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 38 39. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 39 40. Structure of glyceraldehyde 3-phosphate dehydrogenaseActive site: Cys 149, His 176 adjacent to NADMUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 40 41. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 41 42. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 42 43. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 43 44. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 44 45. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 45 46. Free energy profiles for glyceraldehyde oxidation followed byAcyl-phosphate formation: A) Hypothetical B)ActualMUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 46 47. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 47 48. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 48 49. 7: FORMATION OF ATP FROM 1,3-BisPGLYCERATE AND ADPThis step is a substrate-level phosphorylation in which theproduction of a high-energy P is coupled to the conversion ofsubstrate to product, instead of resulting from oxidativephosphorylation. The energy trapped in this new high-energy P willbe used to make ATP in the next reaction of glycolysis. Theformation of ATP by P group transfer from a substrate such as 1,3-bisphosphoglycerate is referred to as a substrate-levelphosphorylation. Unlike most other kinases, this reaction isreversible.2 mols 1,3biPGlycerate 2ATP replaces the 2ATP consumedearlier with the formation of G-6-P and fructose 1,6bisP.MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 49 50. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 50 51. More reactions8. SHIFT OF THE P FROM CARBON 3 TO CARBON 29. DEHYDRATION OF 2-PHOSPHOGLYCERATE Pyruvate first appears in its enol form.10. FORMATION OF PYRUVATE Another substrate-level phosphorylation.MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 51 52. MUHAMMAD RAMZAN UL REHMAN STUDYLOVERS.COM 52 53. 8. SHIFT OF THE P FROM CARBON 3 TO CARBON 2MUHAMMAD R