Glycolysis and Gluconeogenesis
GlycolysisWhat is glycolysis?sequence of reactions that converts one molecule of glucose to two molecules of pyruvate with the formation of two ATP moleculesanaerobic
GlycolysisWhy is glucose such a commonly used fuel?tends to exist in ring form, very stable, doesnt generally glycosylate proteinsformed from formaldehyde under prebiotic conditions
GlycolysisWhat are the possible fates of glucose?
GlycolysisWhats the difference between a facultative anaerobe and an obligate anaerobe?Can you give an example of habitat-dependent anaerobiosis?What about activity-dependent anaerobiosis?
GlycolysisAll the intermediates in glycolysis have either 3 or 6 carbon atomsAll of the reactions fall into one of 5 categoriesphosphoryl transferphosphoryl shiftisomerizationdehydrationaldol cleavage
GlycolysisEntire reaction sequence may be divided into three stagesglucose is trapped and destabilizedsix carbon molecule is split into two three carbon moleculesATP is generated
Glycolysis Stage 1glucose converted to glucose-6-PO4ATP is neededcatalyzed by hexokinase or glucokinaseinduced fit G01= -4.0 kcal/mole
Glycolysis Stage 1phosphoglucoisomerasealdose is converted to ketoseG01=+0.4 kcal/mole
Glycolysis Stage 1rate limiting enzyme allostericinhibited by high ATP, citric acid, long-chain fatty acidsstimulated by ADP or AMPG01= - 3.4 kcal/mole
Glycolysis Stage 2six carbon molecule split into 2- 3 carbon moleculesaldose and ketoseG01=+ 5.73 kcal/mole
Glycolysis Stage 3At equilibrium most mixture exists as dihydroxyacetone phosphateG01=+ 1.83 kcal/mole
Triose Phosphate Isomerase
Glycolysis Stage 3redox reactionenergy from redox used to form acyl phosphateG01= +1.5 kcal/mole
Glycolysis Stage 3Consists of two coupled processes
Glycolysis Stage 3formation of ATP substrate level phosphorylation
Glycolysis Stage 3phosphoryl shift uses 2,3 bisphosphoglycerate G01= +1.1 kcal/moledehydration G01 = +.44 kcal/molephosphoryl transfer G01 = -7.5 kcal/mole
Fate of Pyruvate
Alcoholic FermentationWhich organisms carry out this process?yeastother microorganismsPDC requires thiamine pyrophosphate as coenzymeNAD+ is regenerated
Lactic Acid FermentationOccurs in muscle cells, microorganismsRegenerates NAD+
NAD+ and DehydrogenasesVarious dehydrogenases have a similar binding domain for NAD+ showing their common originRossman fold
GlycolysisHow can fructose be used for energy?
GlycolysisTo use galactose it must be converted to glucose-6-PO4
GlycolysisWhat causes lactose intolerance?
GlycolysisWhat is galactosemia?inability to metabolize galactosemissing galactose 1-phosphate uridyl transferaseliver diseasedevelopment of cataractsCNS malfunction
Control of GlycolysisOf what value is glycolysis for cells?provides energy in form of ATPprovides building blocks for synthetic reactions
Where are most control points found?enzymes that catalyze irreversible reactionshexokinasephosphofructokinasepyruvate kinase
PhosphofructokinaseMost important control point in mammalian glycolytic pathwayallosteric enzymeactivated by AMP and fructose 2,6 bisphosphateinhibited by high levels of ATP, citrate, fatty acids
HexokinaseHexokinase is inhibited by its product glucose-6-PO4glucose remains in bloodGlucokinase, an isozyme of hexokinase is not inhibited by glucose-6-PO4found in liverhas lower affinity for glucose
Pyruvate KinasePyruvate kinase exists as isozymesL form predominates in liverM form mostly in muscle and brainPK is an allosteric enzymeactivated by fructose 1,6 bisphosphateinhibited by ATP, alanineL form of PK influenced by covalent modificationinhibited by phosphorylation
Glucose TransportWhat is the role of glucose transporters in animal cells?facilitate movement of glucose across cell membraneWhat kind of molecule is a transporter and where is it located?small protein embedded in plasma membrane
Glucose Transportmammalian glucose transporter
Glycolysis and CancerWhy are rapidly growing tumor cells dependent upon glycolysis?insufficient oxygen supplyWhat is the function of HIF-1?hypoxia-inducible transcription factor stimulates synthesis of many glycolytic enzymes and GLUT-1 and 3also stimulates vascular endothelial growth factor
GluconeogenesisWhat is gluconeogenesis?synthesis of glucose from non-carbohydrate precursorsWhy is this an important pathway?What are some of the major precursors?lactate, amino acids, glycerolWhere does this process occur?liver, kidney
GluconeogenesisIf gluconeogenesis involves the conversion of pyruvate to glucose why is it not simply the reverse of glycolysis?glycolysis contains several irreversible reactionsWhich reactions in glycolysis are irreversible?phosphoenolpyruvate to pyruvatefructose 6-phosphate to fructose 1,6-bisphosphateglucose to glucose 6-phosphate
GluconeogenesisWhat is the first reaction?
GluconeogenesisWhy is pyruvate carboxylase of special interest?structural propertiescontains ATP-grasp domain at N-terminal endcontains biotin-binding domain at C-terminal end
GluconeogenesisWhat is the role of biotin in this reaction?prosthetic group lined to -amino group of lysine residuecarrier of activated carbon dioxide
GluconeogenesisPyruvate carboxylase is an allosteric enzymeactivated by acetyl CoAneeded to form carboxybiotin
GluconeogenesisCarboxylation of pyruvate occurs in the mitocondria but next step in reaction sequence occurs in cytosol
GluconeogenesisDecarboxylation of oxaloacetate is coupled withphosphorylation by GTPenzyme is phosphoenolpyruvate carboxykinase
GluconeogenesisWhich other steps in glycolysis are irreversible?conversion of fructose 1,6-bisphosphate to fructose 6-phosphateconversion of glucose 6-phosphate to glucose
GluconeogenesisG = -16.7 kJ mol-1fructose-1,6-bisphosphatase is an allosteric enzyme, inhibited by AMP and activated by ATP
GluconeogenesisEnzyme that catalyzes last reaction not found in all tissuesliver and kidney cortex
GluconeogenesisIs gluconeogenesis an energetically favorable reaction in the cell?
What drives this reaction?
Are glycolysis and gluconeogenesis active at the same time?
Regulation of Glycolysis and GluconeogenesisWhat are some of the factors that ensure the reciprocal regulation of these processes?allosteric regulators of key enzymesenergy chargefructose 2,6-bisphosphatehormones
Regulation of Glycolysis and Gluconeogenesis
Regulation of Glycolysis and Gluconeogenesisfructose 2,6-bisphosphate stimulates PFK and inhibits fructose 1,6-bisphosphasecontrolled by insulin and glucagon and reflects the nutritional status of the cell
Regulation of Glycolysis and GluconeogenesisHow do hormones influence the enzymes associated with these processes?influence gene expressionchange transcription rateinfluence degradation of m-RNAinsulin PFK, PKglucagon PEPCK, fructose 1,6-bisphosphatase
Regulation of Glycolysis and GluconeogenesisWhat are substrate cycles and why are they important?can amplify metabolic signalscan generate heat
Regulation of Glycolysis and GluconeogenesisWhat is the Cori cycle and why is it important?
Regulation of Glycolysis and Gluconeogenesis