Energy Metabolism I Glycolysis PDF

Energy metabolism I: Glycolysis Jorge Miguel, MD. W E MAKE DOCTORS Main bibliography Today's lecture is based on: The full book can be found in Clinical Key in your digital resources. AMBOSS Threads...

Energy metabolism I: Glycolysis Jorge Miguel, MD. W E MAKE DOCTORS Main bibliography Today's lecture is based on: The full book can be found in Clinical Key in your digital resources. AMBOSS Threads Recommended pre- Today’s lecture Further reading lecture How can I prepare for future lectures? Learning objectives Define glycolysis and its metabolic importance. Outline the 10 steps in glycolysis. Indicate the primary sites of regulation of glycolysis Describe the role of the enzyme lactate dehydrogenase on glycolysis. Associate the fermentation process with glycolysis. Describe the basic steps of the pentose phosphate pathway.  Energy metabolism Cellular respiration is the production of ATP from glucose oxidation via glycolysis, the Krebs cycle, and oxidative phosphorylation. “These respiratory pathways are essential for energy provision” Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier.  Glycol isis Glucose is the major carbohydrate on Earth, the backbone and monomer unit of cellulose and starch. It is also the only fuel that is used by all cells in our bodies. All of these cells, even the microbes in our intestines, begin the metabolism of glucose by a pathway termed glycolysis - that is, carbohydrate (glyco) splitting (lysis). Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier. Glycol isis Glycolysis, the central pathway of glucose metabolism, is conserved evolutionarily in all cells that use carbohydrates for energy metabolism. Glycolysis pathway converts glucose, a six-carbon sugar, in two molecules of pyruvate, a three-carbon compound. Glycolysis is not only a source of energy, its intermediates are also starting points for numerous other pathways in the cell (amino acid, nucleic acid, and lipid metabolism). Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier. C C C C C C Glucos e C C C C C C  C C C C C C GLUT I, II, III, IV I II III IV C C C C C C C C C C C C C C C C C Glucose C C C C C C Glucose C C C C C C Glucose C C C C C C C C C C C C Glucose Hexokina se C C C C C C  C C C cose Hexokina se C C C Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier. C C C C C C Glucose Hexokina se C C C C C C  C C C C C C Glucose Hexokina ATP se C C C C C C  C C C C C C Glucose Hexokina se 3- PO4 C C C C C C ADP  C C C C C C Glucose Hexokina se 6 5 4 3- 3 2 1 PO4 C C C C C C  C C C C C C Glucose ATP Hexokina se ADP 3- PO4 C C C C C C Glucose-6- phosphate  C C C C C C Glucokina Glucose se ATP Hexokina se Low ADP affinity High affinity 3- PO4 C C C C C C Glucose-6- phosphate  3- PO4 C C C C C C Glucose-6- phosphate 3- PO4 C C C C C C  3- PO4 C C C C C C Glucose-6- phosphate Phosphogluco se isomerase 3- PO4 C C C C C C C C C Isomerization of glucose 6-phosphate to fructose 6-phosphate. 6- e The next step in glycolysis is the isomerization of glucose 6-phosphate to fructose 6- phosphate. The open-chain form of glucose has an aldehyde group at carbon 1, whereas the open-chain form of Phosphogluco fructose has a keto group at carbon 2. Thus, the se isomerase isomerization of glucose 6- phosphate to fructose 6-phosphate is a conversion of an aldose into a ketose. The reaction catalyzed by phosphoglucose isomerase. C C C Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier.  3- PO4 C C C C C C Glucose-6- phosphate Phosphogluco se isomerase 3- PO4 C C C C C C  3- PO4 C C C C C C Glucose-6- phosphate Phosphogluco se isomerase 3- PO4 C C C C C C Fructose-6- phosphate  3- PO4 C C C C C C Fructose-6- phosphate 3- PO4 C C C C C C  3- PO4 C C C C C C Fructose-6- phosphate Phosphofruc to-kinase-1 3- PO4 C C C C C C  3- PO4 Formation of Fructose 1,6-bisphosphate from Fructose 6-phosphate Fructose 6-phosphate is phosphorylated by ATP to fructose 1,6-bisphosphate (F-1,6- BP). The prefix bis- in bisphosphate means that two separate Phosphofruc monophosphate groups are present. This reaction is to-kinase-1 catalyzed by phosphofructokinase (PFK), an allosteric enzyme that sets the pace of glycolysis. 3- PO4 Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier.  3- PO4 C C C C C C Fructose-6- phosphate Phosphofruc ATP to-kinase-1 3- PO4 C C C C C C  3- PO4 C C C C C C Fructose-6- phosphate Phosphofruc to-kinase-1 6 5 4 3- 3 2 1 3- PO4 PO4 C C C C C C ADP  3- PO4 C C C C C C Fructose-6- phosphate ATP Phosphofruc to-kinase-1 ADP 3- 3- PO4 PO4 C C C C C C Fructose-1,6- bisphosphate Investme nt Stage  3- 3- PO4 PO4 C C C C C C Fructose-1,6- bisphosphate  The Six-Carbon Sugar Is Cleaved into Two Three-Carbon Fragments by Aldolase Aldolase The second stage of glycolysis 3- 3- begins with the splitting of PO4 PO4 C C C C C C fructose 1,6- bisphosphate into glyceraldehyde 3- Fructose-1,6- phosphate(GAP) and bisphosphate dihydroxyacetone phosphate (DHAP). This reaction is catalyzed by aldolase. Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier.  3- PO4 C C C C C C 3- PO4 Aldolase  3- PO4 C C C D-Glyceraldehyde 3- phosphate Aldolase 3- PO4 C C C Dihydroxyacetone  3- PO4 C C C D-Glyceraldehyde 3- phosphate Triose phosphate Aldolase isomerase 3- PO4 C C C Dihydroxyacetone  3- PO4 C C C D-Glyceraldehyde 3- phosphate Triose phosphate Aldolase isomerase 3- PO4 C C C Dihydroxyacetone  C C C 3- PO4 Glyceraldehyde 3-phosphate is on the direct pathway of glycolysis, D-Glyceraldehyde 3- whereas dihydroxyacetone phosphate phosphate is not. -Unless a means exists to convert Triose dihydroxyacetone phosphate into phosphate glyceraldehyde 3-phosphate, a three-carbon isomerase fragment useful for generating ATP will be lost. -These compounds are isomers that can be readily interconverted dihydroxyacetone phosphate is a ketose, whereas glyceraldehyde 3-phosphate is an aldose. 3- PO4 C C C -The isomerization of these three-carbon phosphorylated sugars is catalyzed by Dihydroxyacetone triose phosphate isomerase. Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier.  3- PO4 C C C - 3- PO4 C C C D-Glyceraldehyde 3- phosphate  3- PO4 C C C Glyceralde hyde-3- phosphate dehydrogen ase 3- PO4 C C C D-Glyceraldehyde 3- phosphate  3- PO4 C Conversion of glyceraldehyde 3-phosphate into 1,3- bisphosphoglycerate The next step is the conversion of glyceraldehyde 3- phosphate into 1,3-phosphate dehydrogenase Glyceralde hyde-3- phosphate dehydrogen ase 3- PO4 C ldehyde 3- Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier.  3- PO4 C C C Glyceralde hyde-3- Pi phosphate NAD+ dehydrogen ase 3- PO4 C C C D-Glyceraldehyde 3- phosphate  3- 3- PO4 PO4 C C C Glyceralde hyde-3- phosphate dehydrogen ase 3- PO4 C C C NADH D-Glyceraldehyde 3- phosphate  3- 3- PO4 PO4 C C C 1,3-bisphosphate glycerate Glyceralde Pi hyde-3- phosphate NAD dehydrogen ase + NADH 3- PO4 C C C D-Glyceraldehyde 3- phosphate  3- 3- PO4 PO4 C C C 3- 3- PO4 PO4 C C C 1,3-bisphosphate  3- 3- PO4 PO4 C C C Phosphoglyce rate Kinase 3- 3- PO4 PO4 C C C 1,3-bisphosphate  3- PO4 C The Formation of ATP from 1,3 Bisphosphoglycerate The final stage in glycolysis is the generation of ATP from the phosphorylated three-carbon metabolites of glucose. Phosphoglycerate kinase catalyzes the transfer Phosphoglycer of the phosphoryl group from the acyl phosphate of ate Kinase 1,3- bisphosphoglycerate to ADP. ATP and 3- phosphoglycerate are the products. 3- PO4 C hosphate Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier.  3- 3- PO4 PO4 C C C ADP Phosphoglycer ate Kinase 3- 3- PO4 PO4 C C C 1,3-bisphosphate ATP PO4 3- C C C 3- PO4 Phosphoglyce rate Kinase 3- 3- PO4 PO4 C C C 1,3-bisphosphate  3- PO4 C C C 3-phosphoglycerate ATP Phosphoglyce rate Kinase ADP 3- 3- PO4 PO4 C C C 1,3-bisphosphate  3- PO4 C C C 3-phosphoglycerate 3- PO4 C C C  3- PO4 C C C 3-phosphoglycerate Phosphoglycer ate Mutase 3- PO4 C C C  3- PO4 C Generation of Additional ATP and the oglycerate Formation of Pyruvate The first reaction is a rearrangement. The position of the phosphoryl group shifts in the conversion of 3- phosphoglycerate into 2-phosphoglycerate, a reaction Phosphoglycer catalyzed by phosphoglycerate mutase. ate Mutase 3- PO4 C Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier.  3- PO4 C C C 3-phosphoglycerate Phosphoglyce rate Mutase 3- PO4 C C C  3- PO4 C C C 3-phosphoglycerate Phosphoglyce rate Mutase 3- PO4 C C C  3- PO4 C C C 3-phosphoglycerate Phosphoglyce rate Mutase 3- PO4 C C C 2-phosphoglycerate  3- PO4 C C C 2-phosphoglycerate 3- PO4 C C C  3- PO4 C C C 2-phosphoglycerate Enolase 3- PO4 C C C 3- 4 C In the next reaction, an enol is formed by the dehydration of 2-phosphoglycerate. The phoglycerate Enolase catalyzes the formation of phosphoenolpyruvate (PEP). Enolase 3- 4 C Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier.  3- PO4 C C C 2-phosphoglycerate H2O Enolase 3- PO4 C C C phosphoenolpyruvate  3- PO4 C C C phosphoenolpyruvate (PEP) 3- PO4 C C C  3- PO4 C C C phosphoenolpyruvate (PEP) Pyruvate Kinase 3- PO4 C C C  3- O4 Hence, pyruvate is formed, and ATP is generated concomitantly. The virtually irreversible transfer of C a phosphoryl group from phosphoenolpyruvate to ADP is catalyzed by pyruvate kinase. olpyruvate Pyruvate Kinase 3- C Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier.  3- PO4 C C C phosphoenolpyruvate (PEP) Pyruvate Kinase 3- PO4 ADP C C C  3- PO4 C C C phosphoenolpyruvate (PEP) Pyruvate Kinase PO4 ATP 3- C C C  3- PO4 C C C phosphoenolpyruvate (PEP) ATP Pyruvate Kinase ADP C C C Pyruvate x 2 x 2 x 2 x x NET 2 Reaction Glucose + 2 ADP + 2 NAD+ + 2 Pi x 2 2 pyruvate + 2 ATP +2 NADH + 2 H20 x + 2 H+ 2 x Glycol isis The net reaction in the transformation of glucose into pyruvate is: Thus, two molecules of ATP are generated in the conversion of glucose into two molecules of pyruvate Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier. Glycolisis Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier. Regulation of glycolisis The balance between ATP consumption and production is controlled allosterically by three sites: the hexokinase, phosphofructokinase-1, and pyruvate kinase reactions. Each enzyme has the characteristic features of a regulatory enzyme: they are dimeric or tetrameric enzymes whose structure and activity are responsive to allosteric modulators, and they catalyze irreversible reactions. Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier.  C C C C C C Glucose ATP Hexokin G6 ase P ADP 3- PO4 C C C C C C Glucose-6- phosphate  ATP 3- PO4 C C C C C C Citra te Fructose-6- phosphate ATP Phosphofruc to-kinase-1 ADP 3- 3- PO4 PO4 C C C C C C Fructose-1,6- AMP bisphosphate  3- PO4 ATP Citra C C C te phosphoenolpyruvate (PEP) ATP Pyruvate Kinase ADP C C C Pyruvate Anaerobic conditions Anaerobic conditions O2 Infection Hypoxia Ischaemia Heart failure  Lactat e Oxaloacet ate Acetyl- Alanin CoA e C C C Pyruvate Lactat e Lactate dehydrogenas e C C C Pyruvate ctat LDH regenerates NAD+ consumed in the GAPDH reaction, producing lactate, the end product of anaerobic glycolysis. Because NAD + is present in only catalytic amounts in the cell and is an essential cofactor for glycolysis Lactate (and other reactions), there must be a mechanism dehydrogenas for regeneration of NAD + if glycolysis is to continue. e The oxidation of NADH is accomplished under anaerobic conditions by lactate dehydrogenase (LDH), which catalyzes the reduction of pyruvate to lactate by NADH + H + and regenerates NAD +. C C In mammals, all cells have LDH, and lactate is the uvate end product of glycolysis under anaerobic conditions. Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier.  Lactat e NAD+ B Lactate dehydrogenas NADH 3 e C C C Pyruvate Anaerobic conditions O2 Infection Hypoxia Ischaemia Heart failure Fermentat ion Fermentation is a general term for anaerobic metabolism of glucose, usually applied to unicellular organisms. Some anaerobic bacteria, such as lactobacilli, produce lactate. During fermentation in yeast, the pathway of glycolysis is identical to that in the RBC, except that pyruvate is converted into ethanol. Baynes, J. W., & Dominiczak, M. H. (2019). Medical Biochemistry (6th ed.). Elsevier.  HMP Shunt (The pentose phosphate pathway)  HMP Shunt (The pentose phosphate pathway) Goal: Produce NADPH NADPH is required for: -Glutathione reduction -Fatty acid synthesis is Glutathione -Cholesterol required for: synthesis -Free radical detoxification  Glycoly sis HMP Shunt 3- PO4 C C C C C C Glucose-6-phosphate Glc-6-P NADP+ dehydrogen ase Ribulose 5-P NADPH 6- ibulose 5-P Ribulose 5-P phosphogluconi c lactone NADP+ NADPH 6-  Thank you for your attention! Jorge Miguel, MD. W E MAKE DOCTORS