清华大学生物化学课件糖酵解.ppt

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,清华大学生物化学课件糖酵解,清华大学生物化学课件糖酵解清华大学生物化学课件糖酵解Glycolysis(糖酵解),The process in which a molecule of glucose is degraded in a series of enzyme-catalyzed reactions to yield two molecules of pyruvate.,Glycolysis(,糖酵解,),The process in which a molecule of,glucose,is degraded in a series of enzyme-catalyzed reactions to yield two molecules of,pyruvate,.,Overview on glucose metabolism,The major fuel of most organisms and occupies a central position in metabolism(,G,o,=,-2840 kJ/mol,when completely oxidized).,Can be stored in polymer form(glycogen or starch)or be converted to fat for long term storage.,Can also be oxidized to make NADPH and ribose 5-phosphate via the pentose phosphate pathway.,Is also a versatile precursor for carbon skeletons of almost all kinds of biomolecules.,Major pathways of glucose utilization,Glycolysis,The first stage in the complete oxidation of glucose,An universal,central,pathway of glucose metabolism,The chemistry of the reaction sequence completely conserved during evolution,The first metabolic pathway to be elucidated and probably the best understood,1.The Development of Biochemistry and the Delineation of Glycolysis Went Hand by Hand,In 1897,accidental observation by,Eduard Buchner,:sucrose(as a preservative)was rapidly fermented into alcohol by cell-free yeast extract.,The accepted view that fermentation is inextricably tied to living cells(i.e.,the vitalistic dogma)was shaken and Biochemistry was born:,Metabolism became chemistry,!,In 1900s,Arthur Harden,and,William Young,(Great Britain)found that P,i,is needed for yeast juice to ferment glucose,a hexose diphosphate(fructose 1,6-bisphosphate)was isolated.,They also separated the yeast juice into two fractions:one heat-labile,nondialyzable,zymase,(enzymes)and the other heat-stable,dialyzable,cozymase,(metal ions,ATP,ADP,NAD,+,).,1910s-1930s,Gustav Embden,and,Otto Meyerhof,(Germany),studied muscle and its extracts:,Reconstructed all the transformation steps from glycogen to lactic acid,in vitro,;revealed that many reactions of lactic acid(muscle)and alcohol(yeast)fermentations were the same!,Discovered that lactic acid is reconverted to carbohydrate in the presence of O,2,(,gluconeogenesis,);observed that some phosphorylated compounds are energy-rich.,The whole pathway of glycolysis(from glucose to pyruvate)was elucidated by the 1940s.,Basic facts about glycolysis,Ten steps of reactions,are involved in the pathway.,Six types of reactions occur,:group transfer,isomerization,aldol cleavage,dehydrogenation,group shift,and dehydration.,All the enzymes are found in the,cytosol,.,All intermediates are,phosphorylated,.,Only a small fraction,(5.2%),of the potential energy of the glucose molecule is released and much still remains in the final product of glycolysis,pyruvate,.,2.,The overall glycolytic pathway can be divided into two phases,Preparatory phase:,Glucose is converted into glyceraldehyde 3-phosphate,consuming ATP.,Payoff phase:,Glyceraldehyde 3-phosphate is oxidized to generate pyruvate,generating ATP and NADH.,Group,transfer,Isomerization,Group,transfer,Aldol cleavage,Isomerization,Isomerization,Dehydrogenation,Group transfer,Group shift,Dehydration,Group transfer,Irreversible in cells,MgATP,2-,not ATP,4-,is the actual substrate,Preparatory Phase,Step 1,Irreversible,exergonic,Aldose,Ketose,Reversible,Preparatory Phase,Step 2,Reversible,Preparatory Phase,Step 3,The commitment step,(PFK1),Irreversible,exergonic,Preparatory Phase,Step 4,The“lysis”step,Ketose,Aldose,Ketose,Aldose,Step 5,Preparatory Phase,Reversible,Ketose,Group,transfer,Isomerization,Group,transfer,Aldol cleavage,Isomerization,Two molecules,of ATP are,consumed,Step 6,Oxidation and phosphorylation reaction,Payoff Phase,Acyl phosphate,Payoff Phase,Step 7,Substrate-level,phosphorylation,for ATP generation,Payoff Phase,Step 8,2,3-bisphosphoglycerate is both a coenzyme,and an intermediate of the reaction,Payoff Phase,Step 9,Reversible,Payoff Phase,Step 10,Substrate-level,phosphorylation,for ATP generation,Spontaneous,Isomerization,Dehydrogenation,Group transfer,Group shift,Dehydration,Group transfer,Four molecules of ATP and,two molecules of NADH,are generated,The chemical logic of,the glycolytic pathway,A net gain of two ATP,two NADH,two molecules of pyruvate are resulted when a glucose molecule is oxidized via the glycolysis pathway:,Glucose+2 ADP+2P,i,+2NAD,+,2 pyruvate+2ATP+2H,2,O+,2NADH+2H,+,G,o,=,-85,kJ/mol,Glucose,Glucose 6-phosphate,Fructose 1,6-bisphosphate,+Glyceraldehyde 3-phosphate,Dihydroxyacetone phosphate,Glyceraldehyde 3-phosphate(2),1,3-Bisphosphoglycerate(2),3-Phosphoglycerate(2),2-Phosphoglycerate(2),Phosphoenolpyruvate(2),Pyruvate(2),hexokinase,phosphofructokinase-1,phosphohexose isomerase,aldolase,triose phosphate isomerase,glyceraldehyde 3-phosphate dehydrogenase,enolase,phosphoglycerate mutase,pyruvate kinase,ATP,2NADH,ADP,ATP,ADP,2ATP,2ADP,2Pi,2NAD,+,2ATP,+H,+,2ADP,Fructose 6-phosphate,phosphoglycerate kinase,Importance of phosphorylated intermediates,Negatively charged,cant diffuse out of the cell,therefore,no energy is needed to retain them in the cell,Energy conserved in the phosphorylated compounds,Lower the activation energy and increase specificity of the enzymatic reactions,Fates of pyruvate,Serve as a precursor,in anabolic reactions,3.,Fermentation:pyruvate is converted to lactic acid or ethanol under,anaerobic,conditions,This occurs to regenerate NAD,+,for the glycolysis pathway to continue when O,2,lacks.,Lactic acid fermentation:pyruvate is reduced to lactate by NADH,catalyzed by lactate dehydrogenase.,The lactate produced in muscle can be converted back to glucose by gluconeogenesis in the liver of vertebrates(via the,Cori cycle,).,Pyruvate is reduced to lactate when O,2,lacks,in a reaction catalyzed by lactate dehydrogenase,Named for the,reverse reaction,The Cori cycle,Ethanol fermentation,(occurring in yeast and other microorganisms):pyruvate is first decarboxylated and then reduced by NADH,catalyzed by pyruvate decarboxylase and alcohol dehydrogenase respectively.,Thiamine pyrophosphate,(TPP,硫胺焦磷酸,derived from vitamin B,1,)act as the coenzyme of the decarboxylase.,Pyruvate can be reduced to ethanol,in some microorganisms,Present only in,those alcohol,fermentative organisms,Present in many,organisms,including,human,Industrial-scale fermentation,4.,Other hexoses are also oxidized via the glycolysis pathway,They are also first primed by phosphorylation(at C-1 or C-6).,Fructose is primed and cleaved to form dihydroxyacetone phosphate and glyceraldehyde,which are further converted to glyceraldehyde 3-phosphate.,Galactose is first converted to Glucose-1-phosphate via a UDP-galactose intermediate and UDP-glucose intermediate,then to Glucose-6-phosphate.,in liver,in muscle and kidney,Galactose is converted,to glucose-1-phosphate,via a UDP-galactose,intermediate,Several human genetic,diseases result in disordered,galactose metabolism,(,galactosemia,),5.Dietary poly-and disaccharides are hydrolyzed to monosaccharides in the digestive system,Salivary,a,-amylase,(,a,-,淀粉酶,)in the mouth hydrolyzes starch(glycogen)into short polysaccharides or oligosaccharides.,Pancreatic,a,-amylase,(active at low pH)continue to convert the saccharides to mainly maltose and dextrin(from amylopectin,枝链淀粉,).,Specific enzymes on the microvilli of the intestinal epithelial cells finally hydrolyze all disaccharides into monosaccharides.,The monosaccharides are then absorbed at the intestinal microvilli and transported to various tissues for oxidative degradation via the glycolytic pathway.,Adults lacking,lactase,will have,lactose intolerance syndrome,:the lactose is converted to toxic compounds in the large intestine by the bacteria there,causing abdominal cramps and diarrhea.,Lactose+H,2,O D-galactose+D-glucose,lactase,6.Glycogen and starch are degraded by phosphorolysis,The glucose unit at the nonreducing terminal of glycogen is removed as glucose 1-phosphate via phosphorolysis catalyzed by,glycogen phosphorylase,.,Glucose 1-phosphate is then converted to glucose 6-phosphate by,phosphoglucomutase,.,No ATP needed!,Glycogen breakdown by glycogen phosphorylase,A bifunctional,debranching enzyme,aids,the phosphorylase in,degrading glycogen,(Figure 15-26),7.Pentose phosphate pathway converts glucose to specialized products needed by the cells,Glucose 6-phosphate+2NADP,+,+H,2,O,ribose 5-phosphate+2NADPH+CO,2,+2H,+,Oxidative reactions,of the pentose,phosphate pathway,Prominent in tissues actively synthesizing fatty acids and steroids,such as mammary gland,adrenal cortex,liver and adipose tissues.,Pentose generated is necessary for biosynthesis of nucleic acids.,If not needed,six five-carbon sugar phosphates are converted to five six-carbon sugar phosphates.,The reverse of this rearrangement,regeneration of six five-carbon sugar phosphate from five six-carbon sugar phosphate occurs in the,Calvin cycle,for photosynthetic fixation of CO,2,in plants(To be discussed in Chapter 20).,General scheme of the pentose phosphate pathway,The regeneration of six-carbon glucose-6-phosphate from five-carbon ribose-5-phosphate in the pentose phosphate pathway(,nonoxidative,),Role of NADPH in regulation,8.Regulation of glycolysis,Regulatory enzymes of glycolysis:,Hexokinase,Phosphofructokinase-1(PFK-1),Pyruvate kinase,They all catalyze,exergonic,and,irreversible,reactions,and are,all regulated by,allosteric effectors,.,Factors that determine the activity of an enzyme,Factors that determine the activity of an enzyme,Allosteric regulation,Protein phosphorylation and dephosphorylation,The rate of glycolysis in mammals is mainly controlled at the step acted by phosphofructokinase-1(PFK-1,),PFK-1 catalyzes an,irreversible and exergonic,reaction,which commits glucose to the glycolysis pathway(away from the pentose phosphate pathway).,PFK-1 is a complex tetrameric enzyme regulated by multiple intracellular signals(allosteric effectors):,ATP,citrate,being negative ones;,AMP,ADP,and,fructose 2,6-bisphosphate,as positive ones.,E.coli,PFK-1,Allosteric regulation of muscle PFK-1 by ATP,Regulators that affect PFK-1 activity,Hexokinase and pyruvate kinase also set the pace of glycolysis,These two enzymes also catalyze irreversible and exergonic reactions.,Pyruvate kinase is allosterically inhibited by ATP,acetyl-CoA,and long-chain fatty acids.,The catalytic activity of the liver pyruvate kinase isozyme(the L type)is also controlled by reversible phosphorylation.,Hexokinase isozymes are regulated differently.,Regulation of pyruvate kinase,Different roles of muscle and liver in glucose metabolism,Muscle consumes glucose,using it for energy production.,Liver produces and distributes glucose for other tissues,maintaining a constant blood glucose level.,Liver and muscle hexokinase isozymes are regulated differently,Muscle hexokinase,is allosterically inhibited by its reaction product glucose 6-phosphate,which accumulates when PFK-1 is inhibited.,Liver hexokinase,(also called hexokinase IV or glucokinase)has about 100 X less affinity for glucose than that in muscle,therefore,is regulated by the level of blood glucose.,Liver hexokinase,is,not,inhibited by glucose 6-phosphate:,its main role is to convert excess glucose to glucose-6-phosphate for glycogen synthesis,.,Comparison of kinetic properties of,liver Hexokinase IV and muscle Hexokinase,I,(Liver),(Muscle),Glycogen phosphorylase isozymes,Two isozymes exist:one in liver and one in muscle,Both are in two interconvertible forms:the,a,form is phosphorylated and more active;the,b,form is dephosphorylated and less active.,Both phosphorylation and dephosphorylation occur and catalyzed by specific,phosphorylase,b,kinase,and,phosphorylase,a,phosphatase,respectively.,Covalent modification of glycogen phosphorylase,Glycogen phosphorylase kinase is regulated by different hormones in muscle and in liver,In muscle,by,epinephrine,(,肾上腺素,),-secreted by the medulla of the adrenal gland,(,肾上腺髓质,),In liver,by,glucagon,(,胰增血糖素,),-secreted by the pancreas,Cascade mechanism of,epinephrine and,glucagon action,Glycogen phosphorylase is also regulated allosterically,but differently in muscle and liver,In muscle:,Ca,2+,binds and activates phosphorylase,b,kinase.,AMP,binds and activates phosphorylase,b,.,ATP,inactivates phosphorylase.,In liver:,glucose,binds to the,a,form of enzyme,exposing the phosphorylated Ser residues to the action of phosphorylase,a,phosphatase and converting it to the less active,b,form.,The liver glycogen phosphorylase,a,is,negatively regulated by glucose,therefore,can function as a,glucose sensor,Glycolysis and gluconeogenesis are coordinately regulated to avoid the wasteful“futile cycling”,Gluconeogenesis:The pathway converting simple precursors(e.g.,pyruvate and lactate)to glucose,mainly occurring in the,liver,of mammals.,Gluconeogenesis uses most of the same enzymes of glycolysis,but the three exergonic irreversible reactions(catalyzed by the three regulatory enzymes)are detoured(bypassed).,Bypass reaction,The unique enzymes catalyzing the two reversing reactions at one detouring step are,reciprocally,regulated by common allosteric effectors:,fructose 2,6-bisphosphate,activates PFK-1(thus activate glycolysis)and at the same time inhibits fructose 1,6-bisphosphatase 1 or FBPase-1(thus inhibit gluconeogenesis).,Enzymes catalyzing the non-common steps of paired catabolic and anabolic pathways are often reciprocally regulated to avoid futile cycling.,Keywords,Glycolysis,-3 irreversible reactions,Pentose phosphate pathway,-products,PFK-1,-commitment step,regulation,Glycogen phosphorylase,-regulation,Words of the week,aerobic(,有氧的,),vs.anaerobic(,厌氧的,),selfish,vs.,selfless,mono,di,tri,tetra,penta,hexa,hepta,octa,Summary,Glucose is a commonly used fuel and versatile precursor in almost all organisms.,The study of glucose degradation has a rich history in biochemistry(especially for enzymology).,Glucose is first converted into two three-carbon pyruvate via the ten-step glycolysis pathway without directly consuming O,2,and with a net production of two ATP molecules by substrate-level phosphorylation.,Limited amount of energy can be released by oxidizing glucose under anaerobic conditions by fermentation.,The sugar units on glycogen is converted to glucose 1-phosphate via phosphorolysis,which is catalyzed by glycogen phosphorylase.,Other monosaccharides are also converted to intermediates of glycolysis for further oxidative degradation.,Glucose 6-phosphate can also be oxidized to form ribose 5-phosphate and NADPH via the pentose phosphate pathway.,Phosphofructokinase-1(PFK-1)is the main point of regulation for controlling the rate of glycolysis.,The activity o