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glycolysis series of 10 enzyme-catalyzed reactions by which glucose is oxidized to two molecules of pyruvate fate of pyruvate in aerobic conditions oxidation and decarboxylation to acetyl-CoA (3CO2+2H2O) fate of pyruvate in anaerobic condition (contracting muscle) reduction to lactate fate of pyruvate in anaerobic condition (fermentation in yeast) reduction to ethanol second phase of glycolysis (steps 6 to 10) produce 4 ATP (for a net gain of 2ATP) overall mechanism of 2nd phase of glycolysis glyceraldehyde-3-phosphate to pyruvate (same in all organisms) step 6. Glyceraldehyde-3-phosphate dehydrogenase both oxidizes and phosphorilates glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate cofactor in step 6 NAD+ reduced to NADH (which must be eventually reoxidized to NAD+, or else glycolysis will come to a halt) step 7. Phosphoglycerate kinase transfer of phosphate group from 1,3-biphosphoglycerate to ADP results in 3-phosphoglycerate+ATP step 7 is example of substrate-level phosphorylation what does the release of phosphoryl group do in this reaction? release a large amount of free energy which is used to drive the formation of ATP step 8: phosphyglycerate mutase 3-phosphoglycerate is converted to 2-phosphoglycerate (freely reversible reaction) step 9: enolase Enolase catalyzes dehydration reaction eliminating water and turning 2-phosphoglycerate into phosphoenolpyruvate step 10: pyruvate kinase converts phosphoenolpyruvate to pyruvate and transfers a phosphoryl group to ADP to produce ATP role of tautomerization in step 10? first part (removal of phosphoenolpyruvate's phophoryl group) of reaction does not have enough free E to drive the synthesis of ATP from ADP+Pi. So through second part (this is tautomerization) which is highly exergonic, the reaction can move forward. ATP is produced at which steps of second phase? step 7(phosphoglycerate kinase) and 10 (pyruvate kinase) glycolysis needs a continuing supply of NAD+ (by reoxidizing NADH to NAD+) what does enzyme lactate dehydrogenase do? - reduces pyruvate to lactate to regenerate NAD+ in the absense of oxygen - requires NADH to catalyze the conversion of pyruvate to lactate pyruvate + NADH + H+ --> Lactate + NAD+ pyruvate to ethanol two step pathway of yeasts to regenerate NAD+ 1) decarboxylation of pyruvate to acetaldehyde 2) reduction of acetaldehydy to ethanol pyruvate decarboxylase pyruvate decarboxylated to acetaldehyde+CO2 alcohol dehydrogenase acetaldehyde reduced to ethanol and NAD+ regenerated pyruvate to CO2 - path of pyruvate of most aerobic organisms - pyruvate is converted to acetyl co-A -> then processed through the TCA to CO2 pyruvate's carbon atoms - are not always destined for catabolism - they may provide the raw material for synthesizing a variety of molecules How is fat produced from excess carbohydrate? acetyl-coA, derived from pyruvate, can synthesize fatty acids (precursors of triacylglycerols) pyruvate can synthesize what 4-carbon molecule? Oxaloacetate -> which is an intermediate in the synthesis of several amino acids Pyruvate carboxylase pyruvate is converted to oxaloacetate by the carboxylase reaction of pyruvate carboxylase (from 3-C to 4-C) Gluconeogenesis - used in many occasions when the glycolytic pathway needs to be run in reverse (ex: when blood glucose becomes low, glucose needs to be released from the liver into the bloodstream) - when sotred liver glycogen is depleted, glucose is synthesized by the reverse of glycolysis - process requires energy input - most of the steps in glycolysis is reversible - 3 steps are not - these steps need to be circumvented for gluconeogenesis to occur essence of gluconeogenesis two molecules of pyruvate converted to one mole of glucose 3 irreversible steps of glycolysis pyruvate kinase, phosphofructokinase, and hexokinase the three irrerversible reactions are bypassed in gluconeogenesis by.. the four enzymes reversing step 10 pyruvate kinase 1) pyruvate is carboxylated by pyruvate carboxylase to oxaloacetate 2) oxaloacetate is decarboxylated by phosphoenolpyruvate carboxykinase to form phosphoenolpyruvate both steps are enegitically costly pyruvate carboxylase consumes ATP phosphoenolpyruvate consumes GTP main sources of gluconeogenesis are amino acids (since they can all be converted to oxaloacetate and then to phosphoenolpyruvate) fructose bisphosphatase reverses phosphofruktokinase glucose-6-phosphatase reverses hexokinase major regulatory point of gluconeogenesis between the interconversion of fructose-6-phosphate and fructose-1,6-bisphosphate fructose-2,6-bisphosphate is a potent inhibitor of fructose bisphosphatase and also potent activator of phosphofructokinase if fructose-2,6-bisphosphate is high glycolysis is stimulated and gluconeogenesis inhibited UDP-glucose the substrate for glycogen synthase glycogen synthesis glycogen degradation is thermodynamically spontaneous, glycogen synthesis requires input of free energy glycogen synthesis step 1: phosphoglucomutase glucose-6-phosphate (the penultimate product of gluconeogenesis) is converted to glucose-1-phosphate by phosphoglucomutase step 2: formation of UDP-glucose glucose-1-phosphate is "activated" by reacting with UTP and forms UDP-glucose , then inorganic pyrophosphatase cleaves phosphoanhydride bond step 3: glycogen synthase transfers the glucose unit to the C4 OH group at the end of one glycogen's branches to extend the linear polymer of alpha-linked residues the energetic price for adding one glucose unit to glycogen is the cleavage of one phophoanhydride bond of UTP (nucleotides are also required for synthesis of other saccharides) glycogenolysis 1) glycogen is phophorlyzed,(not hydrolyzed), to yield glucose-1-phosphate 2) glucose-1-phosphate turns into glucose-6-phosphate by phosphoglucomutase 3) glucose-6-phosphate is hydrolyzed by gluclose-6-phosphatase and releases free glucose where does this free glucose go? leaves the cell and enters the bloodstream Pentose phosphate pathway - an oxidative pathway for producing NADPH and converting glucose to ribose - glucose is also a precursor of the ribose groups used for nucleotide sythesis - as much as 30% of glucose in the liver may be catabolized ty this pathway different from glycolysis in that this pathway generates NADPH rather than NADH ( these two cofactors are not interchangeable) pentose phosphate pathway is divided into two phases 1) series of oxidative reactions 2) series of reversible interconversion reactions glucose-6-phosphate dehydrogenase catalyes irrerversible transfer of a hydride ion from glucose-6-phosphate to NADP+, forming a lactone and NADPH 6-phospho-gluconolactonase hydrolyze 6-phosphoglucono-lactone to 6-phosphogluconate 6-phosphogluconate dehydrogenase o oxidatively carboxylizes 6-Phosphogluconate to Ribulose-5-phosphate and reduces a second NADP+ to NADPH 2 molecules of NADPH produced for each glucose is primarily used for fatty acid and deoxynucleotides synthesis ribose carbons can also be used in glycolysis and gluconeogenesis by rearrangement of products primary role of pentose phosphate pathway is to produce 1) NADPH 2) ribose-5-phosphate function of NADPH is to serve as cofactor in reductive reactions rold of ribose-5-phosphate is for nucleotide biosynthesis