生物化学教学课件：Chapter 6 Metabolism of carbohydrates

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1、Chapter 6 Metabolism of carbohydratesChapter 6 Metabolism of carbohydratesChapter7 Metabolism of LipidsChapter7 Metabolism of LipidsChapter8 Biological oxidationChapter8 Biological oxidation Metabolismmetabolic pathways(代谢途径代谢途径)metabolic intermediates(代谢中间(产)物)称为metabolites(代谢物代谢物).enzyme-catalyzed

2、 reactionsCatabolism(degradation)分解代谢分解代谢 S P1+P2 energyAnabolism(biosynthesis)合成代谢合成代谢S1+S2 Penergy *S:substrate E1 E2 E3 E4 E5E1 E2 E3 E4 E5There are two major types of Metabolic PathwaysEnergy relationships between catabolic and anabolic pathways Catabolic pathways deliver chemical energy in the

3、form of ATP,NADH,NADPH,and FADH2.These energy carriers are used in anabolic pathways to convert small precursor molecules into cell macromolecules.ATP(adenosine triphosphate)is a nucleotide(核苷酸核苷酸)composed of three basic units:phosphate,ribose(核糖核糖),adenine(腺嘌呤腺嘌呤)(guanine for GTP,uracil for UTP,cyt

4、osine for CTP).腺苷三磷酸腺苷三磷酸AMPATPADP+Pi energyATPAMP+PPi energy Pi PiATP provides energy by hydrolysis or group transfer(donating a Pi,PPi or AMP to form covalent intermediates)+Although metabolism embraces hundreds of different enzyme-catalyzed reactions,our major concern is the central metabolic pat

5、hways,which are few in number and remarkably similar in all forms of life.Chapter 6 Metabolism of carbohydratesCarbohydrates can be synthesized from CO2 in photosynthetic organisms In plants,CO2+H2O glucose Starch(storage)In animals,*Carbohydrates are synthesized from fat and protein.*The bulk of ca

6、rbohydrates come from plants(food).自养型生物自养型生物 异养型生物异养型生物葡萄糖果糖hexoses *Disaccharides(二糖)e.g.lactose(乳糖乳糖):Glc-Gal sucrose(蔗糖蔗糖):Glc-Fru maltose(麦芽糖麦芽糖):Glc-Glc trehalose(海藻糖海藻糖):Glc-Glc*Polysaccharides(多糖多糖)starch(Plant glucose storage)glycogen(Animal glucose storage)cellulose(in plant cell walls)&ch

7、itin(in animals)are structural polysaccharides(纤维素纤维素&壳多糖壳多糖)Starch the most important food source of carbohydrate(e.g bread,rice,noodles,potatoes),is a polymer of glucose residues joined by 1,4 bonds and with branches provided by 1,6 bonds.Glycogen(mainly in liver and skeleton muscles)is a polymer

8、of(a1-4)linked glucose units with(a1-6)linked branches(occurring about once every 10 glucose residues,making glycogen a highly branched molecule).GlycogenReduced Non-reduced vglycogenn Food starch is the main source of carbohydrates.n Only monosaccharides can be absorbed in intestine.Section IDigest

9、ion and absorption of carbohydrates-maltose(麦芽糖麦芽糖)(40%)-maltotriose(麦芽三糖麦芽三糖)(25%)limit dextrin(-极限糊精极限糊精)(30%)isomaltose(异麦芽糖异麦芽糖)(5%)Glucose(葡萄糖葡萄糖):salivary-amylase唾液中的唾液中的-淀粉酶淀粉酶 -glucosidase(-葡萄糖苷酶葡萄糖苷酶)limit dextrinase(极限糊精酶极限糊精酶)Digestion 肠粘膜肠粘膜上皮细胞上皮细胞Intestinal mucosal cell (in mouth)肠腔肠腔(

10、in small intestine)pancreatic-amylase胰液中的胰液中的-淀粉酶淀粉酶 Starch in foodTransport of glucose into cellsnFacilitated transport Mediated by a family of at least five glucose transporters in the cell membrane,GLU-1 to GLU-5.Extracellular glucose binds to the transporter,which then alters its conformation,di

11、scharging glucose within the cell.ADP+Pi ATP G Na+K+Na+泵泵小肠粘膜细胞小肠粘膜细胞 肠肠腔腔 门静脉门静脉 吸收机制吸收机制NaNa+依赖型葡萄糖转运体依赖型葡萄糖转运体(Na+-dependent glucose transporter,SGLT)刷状缘刷状缘 细胞内膜细胞内膜 Intestinal mucosal cell 吸收途径吸收途径 肠腔肠腔glucose+Na+Na+-dependent glucose transport protein(SGLT)Intestinal mucosal cell 门静脉门静脉 glucose

12、 transporter(GLUT15)liver blood other tissue cells Glc（Na+依赖型葡萄糖转运体）依赖型葡萄糖转运体）Catabolism of Carbohydrates Three major pathways:1.Glycolysis(糖酵解或糖的无氧氧化)2.Aerobic oxidation(糖的有氧氧化)3.Pentose phosphate pathway2ATPs are producedGlycolysis comes from the Greek glykys,meaning“sweet”,and lysis,meaning“split

13、ting”.Section II Glycolysis or Anaerobic Oxidationenzyme-catalyzed reactions1 glucose 2 pyruvate 2 lactate In glycolysis,a molecule of glucose is degraded in a series of enzyme-catalyzed reactions to yield two molecules of three-carbon compound pyruvate,with energy conserved as ATP and NADH.It occur

14、s in cytosol of all organisms.葡萄糖葡萄糖6 C丙酮酸丙酮酸3 C乳酸乳酸缺缺O2lactateNAD+2H (1)Glucose+ATPGlucose-6-phosphate(G-6-P)+ADP phosphorylation of Glc to form G-6-P Hexokinase(also glucokinase葡萄糖激酶葡萄糖激酶 in liver)catalyzes the first phosphorylation reaction.1 ATP molecule is consumed.Irreversible己糖激酶己糖激酶Hexokinas

15、ev Hexokinase comprise hexokinase,&v Hexokinase,catalyze phosphorylation of hexose to form hexose-6-phosphatev These enzymes can be inhibited by their products v These enzymes have high affinity for glucose.Hexokinase (or glucokinase)Catalyze phosphorylation of Glc to form G-6-P Only distribute in l

16、iver Can not be inhibited by G-6-P Has low affinity for glucose Can be regulated by some hormones(e.g.insulin induce synthesis of E protein)Helps regulate blood glucose in the liver(2)G-6-P Fructose-6-phosphate(F-6-P)*Phosphohexose isomerase catalyzes the isomerization from G-6-P to F-6-P,converting

17、 an aldose to a ketose.*This reaction is reversible磷酸己糖磷酸己糖异构酶异构酶(3)F-6-P +ATP Fructose-1,6-bisphosphate (F-1,6-BP)+ADP Phosphofructokinase-1(PFK-1)catalyzes the reaction.The reaction is irreversible.In the reaction,one ATP molecule is consumed.6-6-磷酸果糖激酶磷酸果糖激酶-1-13 21456(4)F-1,6-BP Dihydroxyacetone

18、 phosphate+Glyceraldehyde-3-phosphate One molecule of hexose is cleaved from the middle C-C bond to yield two molecules of triose.The reaction is reversible.(DHAP,磷酸二羟丙酮）磷酸二羟丙酮）+(PGAL,3-,3-磷酸甘油醛）磷酸甘油醛）醛缩酶醛缩酶(5)Dihydroxyacetone phosphate Glyceraldehyde-3-phosphate 磷酸丙糖磷酸丙糖异构酶异构酶(6)Glyceraldehyde-3-ph

19、osphate+NAD+Pi 1,3-bisphosphoglycerate+NADHEnzyme:glyceraldehyde-3-phosphate dehydrogenase Coenzyme:NAD+3-3-磷酸甘油醛脱氢酶磷酸甘油醛脱氢酶High energy acyl phosphateNAD and NADP are the freely diffusible coenzymes of many dehydrogenases,used in redox reactions.Both NAD+and NADP+accept two electrons and one proton.

20、nicotinamide ring(7)1,3-bisphosphoglycerate+ADP 3-phosphoglycerate+ATP Enzyme:phosphoglycerate kinase Generate one molecule of ATP磷酸甘油酸激酶磷酸甘油酸激酶nATP is formed by the direct transfer of a phosphate group from a high-energy substrate(eg.glycerate-1,3-bisphosphate)to ADP.代谢物在脱氢或脱水过程中产生的高能磷酸键直接转代谢物在脱氢或脱

21、水过程中产生的高能磷酸键直接转移给移给ADP生成生成ATP的过程。的过程。Substrate-level phosphorylation底物水平磷酸化底物水平磷酸化(8)3-phosphoglycerate 2-phosphoglycerate Enzyme:phosphoglycerate mutase Transfer of the phosphoryl group from C3 to C2磷酸甘油酸磷酸甘油酸变位酶变位酶(9)2-phosphoglycerate Phosphoenolpyruvate (PEP)+H2O烯醇化酶烯醇化酶High energy Enzyme:pyruva

22、te kinase Produce one ATP molecule by substrate-level phosphorylation The reaction is irreversible(10)PEP+ADP Pyruvate+ATP丙酮酸激酶丙酮酸激酶Three possible catabolic fates of the pyruvate formed in glycolysisO2缺缺O2缺缺O2Under anaerobic conditions,pyruvate is reducedto lactate in a reactioncatalyzed by lactated

23、ehydrogenase,NAD+as coenzyme.This occurs to regenerate NAD+for the glycolysis pathway to continue when O2 lacks.Pyruvate+NADH+H+Lactate+NAD+(11)Pyruvate is converted to lactateunder anaerobic conditions(LDH)lactateNAD+2HPyruvatelactate丙酮酸生成乳酸丙酮酸生成乳酸 2 nAll enzymes are in the cytosol.nA net gain of t

24、wo ATP,two lactates are resulted when a glucose molecule is oxidized via the glycolysis pathway:Glucose+2 ADP+2Pi 2 lactate+2ATP+2H2O n Net NADH production is zeron Substrate-level phosphorylationphosphoglycerate kinasepyruvate kinaseSummary of Glycolysisn Three irreversible reactions:(1)Glucose+ATP

25、 G-6-P+ADP hexokinase(glucokinase)(2)F-6-P+ATP F-1,6-2P+ADP phosphofructokinase-1(3)Phosphoenolpyruvate+ADP Pyruvate+ATP pyruvate kinasel These three reactions are the major regulation points of glycolysis.Summary of Glycolysis+2 ATPHexokinasePhosphofructokinasePyruvate kinase-1 ATP STEPS ATP Net pr

26、oduction =2 ATP-1 ATPPhosphoglycerate kinase+2 ATPEnergy yieldSummary of GlycolysisSummary of Glycolisisn3 irreversible/key reactions catalyzed bylHexokinase(glucokinase)l6-phosphofructokinase-1lPyruvate kinasenKey enzyme activities are controlled by lAllosteric regulationlChemical modificationlEnzy

27、me concentration2.Regulation of glycolysislactate6-phosphofructokinase-1(PFK-1)is the main regulation point for controlling the rate of glycolysis.Phosphofructokinase-1(PFK-1)is regulated by*Allosteric regulation Allosteric inhibitorsXAllosteric activatorsF-2,6-BP is very strong allosteric activiato

28、r.*Chemical modification PFK-2 and FBP-2 is controlled by glucagon(胰高血糖胰高血糖素素)through chemical modification 柠檬酸柠檬酸Fructose 1,6-bisphosphatePFK-2/FBP-2 受胰高血糖素的（化学修饰）调节受胰高血糖素的（化学修饰）调节nThe most important role of glycolysis is to supply energy(ATP)rapidly in anaerobic condition.(e.g.skeletal muscles con

29、tract vigorously in anaerobic condition).nThe glycolysis is also important for some tissue cells to get energy in aerobic condition:nIt is the sole source of energy in erythrocytes(no mitochondria)nIt provides energy in some mammalian tissues and cell types with very high metabolic activity(nerve ce

30、lls,white blood cell,and marrow cell,for example).3.Physiological roles of glycolysisUnder aerobic conditions,NADH in cytosol are transported into mitochondria by two shuttle systems.NADH will pass their electrons to O2 after being transferred through a series of electron transport chain.The complet

31、e oxidation of NADH leads to the generation of ATP.anaerobic conditionsnGlucoseCO2+H2O+ATPsnAerobic oxidation is major pathwayn50%70%of energy comes from glucose oxidation in human bodynAlmost all cells get energy from aerobic oxidation of glucosenOccurs in cytosol&in mitochondrionSection Aerobic Ox

32、idation of GlucoseO2Stage I:Glucose 2 Pyruvate(In cytosol)Stage II:Pyruvate Acetyl-CoA(Pyruvate must be transported into the mitochondrion)Stage III:Acetyl-CoA CO2+H2O(Citric acid cycle+ETC in mitochondrion)ETC1.Three stages of Aerobic Oxidation(乙酰乙酰CoA)CoA)Hydrogen(NADH,FADH2 by dehydrogenation dur

33、ingcatabolism)O2a series of membrane-bound electron carriers,called the respiratory chain or electron transfer chainH2OADP+Pi ATPenergyH H+eOxidationPhosphorylation*电子传递链电子传递链ETC氧化磷酸化氧化磷酸化(Oxidative phosphorylation)Mitochondria is the major site for fuel oxidation to generate ATP.(1)First Stage:(In

34、cytosol)Glucose 2 ATP 2 NAD+2 pyruvate 4 ATP 2 NADHGlycolytic pathway Pyruvate is first transported into mitochondria via a specific transporter on the inner membrane.Pyruvate is converted to acetyl-CoA and CO2 by oxidative decarboxylation in mitochondria.Pyruvate Acetyl-CoAPyruvate+NAD+HSCoA Acetyl

35、-CoA+NADH+H+CO2Enzyme:pyruvate dehydrogenase complexOxidative decarboxylation(氧化脱羧):combination of two reactions丙酮酸脱氢酶复合体丙酮酸脱氢酶复合体The pyruvate dehydrogenase(PDH)complex is a huge multimeric assembly of three kinds of enzymes each present in multiple copies,having over 60 subunits.n pyruvate dehydrog

36、enase(E1)丙酮酸脱氢酶丙酮酸脱氢酶n dihydrolipoyl transacetylase(E2)二氢硫辛酰胺转乙酰酶二氢硫辛酰胺转乙酰酶n dihydrolipoyl dehydrogenase(E3)二氢硫辛酰胺脱氢酶二氢硫辛酰胺脱氢酶n 5 coenzymes:thiamine pyrophosphate(TPP,B1),lipoic acid(硫辛酸硫辛酸),NAD+(PP),FAD(B2),HSCoA(泛酸泛酸)Coenzyme A(CoA-SH),synthesized from pantothenic acid(Vitamin B5)is the“carrier mo

37、lecules”deliver activated acyl groups(with 2-24 Carbons)for degradation or biosynthesis.Functional group:sulfhydryl group(-SH)FAD and FMN,the flavin nucleotides,are derived from riboflavin(VitaminB2).They serve as tightly bound prosthetic groups of flavoproteins.The oxidized flavin nucleotide can ac

38、cept either one electron(yielding FADH1 or FMNH1)or two(yielding FADH2 or FMNH2).DihydrolipoylThe lipoyl group occurs in oxidized(disulfide)and reduced(dithiol)forms and acts as a carrier of both hydrogen and an acetyl(or other acyl)group.All these enzymes and coenzymes are clustered,allowing the in

39、termediates to react quickly without diffusing away from the surface of the enzyme complex,and the local concentration of the substrate is kept very high.The oxidative decarboxylation of pyruvate is catalyzed bya multiezyme complex:pyruvate dehydrogenase complex.HydroxyethylTPPcatalytic cycle(3)The

40、third stageAcetyl-CoA TCA Oxidative phosphorylationCO2+H2O+ATP2.Tricarboxylic acid cycle,TCA (Citric acid cycle/Krebs cycle)The common pathway leading to complete oxidation of carbohydrates,fatty acids,and amino acids to CO2.A pathway providing many precursors for biosynthesisThe acetyl CoA is compl

41、etely oxidized to CO2 via the citric acid cycle1）Oxaloacetate+Acetyl-CoA Citrate+HSCoA Enzyme:citrate synthase (1)The citric acid cycle consists of eight reactions草酰乙酸草酰乙酸乙酰乙酰CoACoA 2)Citrate is converted to isocitrate via dehydration followed by a hydration step.Enzyme:aconitase 顺乌头酸酶顺乌头酸酶异柠檬酸异柠檬酸顺

42、乌头酸顺乌头酸3)Isocitrate+NAD+-Ketoglutarate+NADH+H+CO2 Enzyme:isocitrate dehydrogenase Oxidative decarboxylation stepThe first oxidation step-酮戊二酸酮戊二酸4)-Ketoglutarate+NAD+SuccinylCoA+NADH +H+CO2 The second oxidation step(E1,E2,E3)TPP lipoate FAD Enzyme:-ketoglutarate dehydrogenase complex closely resembl

43、es the pyruvate dehydrogenase complex in structure and function The second oxidative decarboxylation step-酮戊二酸脱氢酶复合体酮戊二酸脱氢酶复合体琥珀酰琥珀酰CoACoA5）Succinyl-CoA+GDP Succinate+GTPSubstrate-level phosphorylation of GDP(or ADP)to form GTP(or ATP).琥珀酰琥珀酰CoACoA合成酶合成酶琥珀酸琥珀酸GTP +ADP =GDP +ATP6）Succinate +FAD Fumar

44、ate+FADH2 Enzyme：succinate dehydrogenase(An enzyme bound to the inner membrane of mitochondrion)The third oxidation step延胡索酸延胡索酸7）Fumarate+H2O malate (trans)延胡索酸酶延胡索酸酶苹果酸苹果酸8）Malate+NAD+Oxaloacetate+NADH+H+(The fourth oxidation step)Oxaloacetate is regenerated at the endThe citricacid cycleSummary o

45、f reactions4 dehydrogenation:3 NADH+H+,1 FADH22 decarboxylation:2CO21 substrate-level phosphorylation:GDPGTP ATP3 irreversible reactions:nCitrate synthasenIsocitrate dehydrogenase n-ketoglutarate dehydrogenasen It is the final oxidation pathway of carbohydrates,lipids and proteins.Carbohydrates,lipi

46、ds and proteinsacetyl-CoA TCA H2O+CO2+ATPn It is the linkage among the metabolic pathways of carbohydrates,lipids and proteins(An amphibolic pathway serving both the catabolic and anabolic).It provides precursors for the biosynthesis of amino acids,nucleotides,fatty acids,sterols,heme groups,etc.e.g

47、.acetyl-CoA-fatty acid and cholesterol oxaloacetae -aspartate -ketoglutarate -glutamate(2)Physiological roles of Citric Acid CycleNADH enters the respiratory chain to produce 2.5 molecules of ATP.FADH2 enters the respiratory chain to yield 1.5 molecules of ATP.Yield of ATPs in oxidation of 1 acetyl-

48、CoA1 acetyl-CoA Citric acid cycle&ETC 3 NADH+H+3 2.5=7.5 ATP 1 FADH2 1 1.5=1.5 ATP 1 GTP 1 ATP 10 ATP3.Aerobic oxidation of glucose is the major way for human bodies to acquire energy(ATP)H2OH2OH2OH2O2.5ATP1.5ATP 2.5ATP2.5ATPETCETCETCETCTCA cycleElectron transfer chain(ETC)in mitochondria(线粒体电子传递链线粒

49、体电子传递链/呼吸链）呼吸链）NADH electron transfer chain NADH-H2O ATP ATP ATP FADH2 electron transfer chainFADH2-H2O ATP ATPChapter 8O2O2 Yield of ATP Glucose 2 pyruvate(Glycolysis)2 +2NADH(Glycolysis in cytosol)*3 or 5 2 Pyruvate 2 acetyl-CoA 22.5=5 2 Acetyl-CoA 4CO2(Citric acid cycle)210 30 or 32 ATP Aerobic O

50、xidation of Glucose*两种穿梭系统两种穿梭系统(Shuttle system)细胞质中的NADH通过不同的穿梭系统进入线粒体氧化产生的ATP数目不同。n NADH -磷酸甘油穿梭 FADH 1.5ATPn NADH 苹果酸-天冬氨酸穿梭 NADH 2.5ATP(细胞质)(线粒体)4.Regulation of aerobic oxidation based on the energy requirement of cell Pyruvate dehydrogenase complex by allosteric regulationallosteric inhibition:

51、by acetyl-CoA,NADH,ATP,fatty acidsallosteric activiation：by CoASH,NAD+,AMP,ADP by chemical modification：phosphorylation/dephosphorylation *The activity of phosphorylated pyruvate dehydrogenase is decreased.共价修饰调节共价修饰调节 Regulation of TCA cycle Citrate synthaseIsocitrate dehydrogenase -ketoglutarate d

52、ehydrogenase inhibited by NADH/NAD+,ATP/ADP and ATP/AMP activated by Ca2+in mitochondrion The rate of electron transfer chain Glycolysis and Aerobic Oxidation of glucose glycolysis Aerobic Oxidation in anaerobic condition in aerobic condition in cytosol in mitochondrion end product lactate end produ

53、ct CO2+H2O 2 ATP 30ATP/32ATP 5.Pastuer effect(巴斯的效应巴斯的效应)nThe glycolysis process can be inhibited by aerobic oxidation.Section Other metabolic pathways of glucosen This pathway occurs in cytosol n This pathway does not generate ATP,but can produce 2 very important substances:n NADPHn Ribose-5-phosph

54、ate1.Pentose phosphate pathway This pathway can be divided into 2 phases:n Oxidative non-reversible phase producing NADPHn Non-oxidative reversible phase producing ribose and other sugars(1)Reactions of pentose phosphate pathway*a series of rearrangement and group transfer reactions6-6-磷酸葡萄糖酸内酯磷酸葡萄糖

55、酸内酯6-6-磷酸葡萄糖酸磷酸葡萄糖酸5-5-磷酸核酮糖磷酸核酮糖 3Stage 1Stage 2:Regeneration of six-carbon Glucose-6-P from five-carbon Ribose-5-PNonoxidative reactions:a series of rearrangement and group transfer reactions 6NADPH+3 CO2 23 R-5-P R-5-P pathway 2 F-6-P 1 PGALnucleotide and nucleic acid synthesis3 reductive reactio

56、nKey enzyme:G-6-P dehydrogeneaseRegulated by NADPH/NADP+(2)Physiological roles of pentose phosphate pathwayn Provision of ribose 5-phosphate residues for nucleotide and nucleic acid synthesis.n Generation of NADPH needed for reductive biosynthesis or to counter the damaging effects of oxygen radical

57、s n For reductive reaction-fatty acid,cholesterol,etcn For hydroxylation reactionsynthesis of collagen,amino acid,vitamin D3,steroid hormones,bile acids and biotransformation in livern For maintenance of GSH levelhemolysis溶血溶血hemolytic anemia溶血性贫血溶血性贫血 谷胱甘肽过氧化物酶谷胱甘肽过氧化物酶谷胱甘肽还原酶谷胱甘肽还原酶Favism(蚕豆病蚕豆病)O

58、xidative damage to lipids,protein,enzymes,intact of RBC membrane,Hb,DNAdefectSection Metabolism of glycogen(glycogenesis and glycogenolysis)Glycogen(animals)is the major storage form of carbohydrates.n liver glycogen(stored in liver)n maintenance the balance of the blood glucosen muscle glycogen(sto

59、red in muscle)n be oxidized to generate ATPs for muscle contraction-1,4 glycosidic linkage-1,6 glycosidic linkageGlycogenOHhemiacetal hydroxy group半缩醛羟基半缩醛羟基Each glycogen molecule has only one reducing end,but many nonreducing ends.Glycogen is synthesized by using UDP-glucose:G G-6-PE:hexokinaseG-6-

60、P G-1-PE:phosphoglucomutaseUTP+G-1-P PPi+UDP-glucose(UDPG)E:UDPG pyrophosphorylasePPi:pyrophosphate2Pi 1.Glycogen synthesis(glycogenesis)*Occur in cytosol of liver cells and muscle cellsActive form of glucoseGlucose 1-phosphateUDP-glucose pyrophosphorylase-ATP UDPG+(G)n (G)n+1+UDP (primer or glycoge

61、n)glucogen(n+1)E1:glycogen synthase(1218 G)forming-1,4-linkage E2:branching enzyme(transfer 67 G)forming-1,6-linkage The glucose residue of UDP-Glucose is transferred to the nonreducing end of a primer or glycogen branch to make a new-1,4 glycosidic bond in a reaction catalyzed by glycogen synthase.

62、Glycogen is extended from the nonreducing end using UDP-glucose:The glucose residue of UDP-Glucose is transferred to the nonreducing end of a primer or glycogen branch to make a new-1,4 glycosidic bond in a reaction catalyzed by glycogen synthase.UDPG+(G)n (G)n+1+UDPA branching enzyme catalyzes the

63、transfer of a short stretch of Glc residues from one nonreducing end to the more interior of the glycogen to make an 16 linkage(thus forming a branch).-1,4-1,4-糖苷键糖苷键-1,6-1,6-糖苷键糖苷键Glycogenin-a glycoproteintyrosineGlycogen primerUDPGWhere does the primer come from?2.Glycogen degradation(glycogenolys

64、is)(G)n (G)n-1+G-1-P E:glycogen phosphorylase:1,4-bond E:debranching enzyme:1,6-bond (2 kinds of enzyme activity)G-1-P G-6-P E:phosphoglucomutaseG-6-P G E:glucose-6-phosphatase (in liver and kidney,not in muscle)*Occur in cytosol of liver cells and muscle cellsNo ATP Consumed!*G-transferase:transfer

65、 3-G chain*-1,6-glucosidase:hydrolyze-1,6-linkage at branch point to release G3.Regulation of glycogen metabolism Two key enzymes:glycogen phosphorylase glycogen synthase regulated by *chemical modification(important)*allosteric regulation*Phosphorylase-inhibited by G*G-6-P,ATP/AMP Glycogen synthase

66、and phosphorylaseare reciprocallyregulated by hormones viaphosphorylation-dephosphorylationHormones like epinephrine or glucagon will activate protein kinase A,which will lead to phosphorylation modification of both the glycogen phosphorylase(thus activating it)and the glycogen synthase(thus inactivating it).抑制糖原合成抑制糖原合成,促进糖原分解促进糖原分解Chemical modificationLiver glycogen G-1-P G-6-P G blood glucose-6-phosphatase in liver,not in muscle Difference of glycogen metabolism in liver and muscleRegulated b