1、Metabolism of CarbohydratesConcept of carbohydrate 碳水化合物，其化學本質為多羥醛或多羥酮類及其衍生物或多聚物。Classes of carbohydrate monosacchride oligosacchridepolysacchrideglycoconjugate glucose 已醛糖 fructose 已酮糖 Monosacchride galactose 已醛糖 ribose 戊醛糖 Oligosacchridemaltose: glucoseglucose sucrose: glucosefructoselactose: gluc

2、osegalactose能水解生成幾分子單糖的糖，各單糖之間借脫水縮合的糖苷鍵相連。Polysacchride能水解生成多個分子單糖的糖。starchglycogencelluloseStarch: one of the chief forms in which plants store food 淀粉顆粒 glycogen : the forms of glucose stored in the animals Non-reduced Reduced cellulose：食物中含有，人體因無-糖苷酶而不能利用。有刺激腸蠕動等作用。-1,4-糖苷鍵Section IIntroduction P

3、hysiological functions1. Provide the energy-major function2. carbo-sources of other materials in the body: amino acids, fats, cholesterol 3. Components of cells：glycoprotein、proteoglycan 、glycolipid, etc., nucleotides Digestion and Absorption of carbohydratesDigestion of CarbohydratesMonosaccharides

4、Do not need hydrolysis before absorptionVery little (if any) in most feedsDi- and poly-saccharidesRelatively large moleculesMust be hydrolyzed prior to absorptionHydrolyzed to monosaccharidesOnly monosaccharides can be absorbedstarchMaltose +麥芽三糖 （40%） （25%）Dextrin +異麥芽糖 （30%） （5%）glucoseSalivary Am

5、ylase-葡萄糖苷酶-臨界糊精酶 Process of digestion 腸粘膜上皮細胞刷狀緣 stomach MouthSmall IntestinePancreatic AmylaseOverview Monogastric Carbohydrate DigestionLocation Enzymes Form of Dietary CHOMouth Salivary Amylase Starch Maltose Sucrose LactoseStomach (amylase from saliva) DextrinMaltoseSmall Intestine Pancreatic A

6、mylase Maltose Brush Border Enzymes Glucose Fructose Galactose + + + Glucose Glucose GlucoseLarge Intestine NoneBacterial Microflora Ferment Cellulose Carbohydrate Absorptionlocation： duodenum and jejunumformation： monosacchridemechanism：active transportNa+-dependent glucose transporter, SGLTADP+Pi

7、ATP G Na+ K+ Na+pumpIntestinal epithelial cell 腸腔 Portal VeinBrush Border細胞內膜 Carbohydrates MonosaccharidesSmall IntestineActive TransportLiverPortal VeinDistributed to tissue through circulationGLUT (glucose transporter)GLUT 15)Outline of carbohydrate metabolism Glucose酵解途徑 pyruvateAerobicanaerobic

8、H2O及CO2 lactate糖異生途徑 lactate、amino acid、glycerol glycogen肝糖原分解 糖原合成磷酸戊糖途徑 ribose + NADPH+H+starchDigestion and absorption ATP catabolic pathway of carbohydratesanaerobic glycolysisAerobicoxidationpentose pathwaySection IIGlycolysisThe process of glycolysisStage I ：glucose digested to pyruvate Glycol

9、ysis pathway stageII：The conversion of pyruvate to lactate*Definition： Glycolysis is the sequence of reactions that converts glucose into lactate with the concomitant production of ATP,under anaerobic conditions*two stages of glycolysis *the reaction site: cytosol The conversion of glucose to Glucos

10、e-6-phosphateATP ADPMg2+ hexokinaseGlu G-6-P F-6-P F-1,6-2PATP ADP ATP ADP 1,3-diphospho-glycerate3-phospho-glycerate2-phosphoglyceratepyruvateDihydroxyacetone phosphateGlyceraldehyde 3-phosphateNAD+NADH+H+ADPATPADPATPPhosphoenolpyruvate（一）The conversion of one molecule of glucose two molecules of p

11、yruvateATP neededUnreverse reaction Glucose-6-phosphate G-6-PFour types of hexokinase in the mammals (typeto )Type located in the liver cells：appetency to glucose is very lowregulated by hormones The conversion of glucose-6-phosphate to fructose-6-phosphatePhosphoglucoseisomeraseGluG-6-PF-6-PF-1,6-2

12、PATPADPATPADP1,3-diphospho-glycerate3-phospho-glycerate2-phosphoglyceratepyruvateDihydroxyacetone phosphateGlyceraldehyde 3-phosphateNAD+NADH+H+ADPATPADPATPPhosphoenolpyruvateglucose-6-phosphate(G-6-P）fructose-6-phosphate(F-6-P） The conversion of F-6-P to fructose-1,6-diphosphate ATP ADP Mg2+ phosph

13、ofructokinase （FPK）GluG-6-PF-6-PF-1,6-2PATPADPATPADP1,3-diphospho-glycerate3-phospho-glycerate2-phosphoglyceratepyruvateDihydroxyacetone phosphateGlyceraldehyde 3-phosphateNAD+NADH+H+ADPATPADPATPPhosphoenolpyruvateATP neededunreverse (F-6-P）fructose-1,6-Diphosphate(F-1,6-2-P) The conversion of F-1,6

14、-2P converted to 2 molecules of triose phosphate aldolaseGluG-6-PF-6-PF-1,6-2PATPADPATPADP1,3-diphospho-glycerate3-phospho-glycerate2-phosphoglyceratepyruvateDihydroxyacetone phosphateGlyceraldehyde 3-phosphateNAD+NADH+H+ADPATPADPATPPhosphoenolpyruvatefructose-1,6-diphosphate(F-1,6-2P）Dihydroxyaceto

15、ne phosphateGlyceraldehyde 3-phosphate The isomerization of triose phosphateTriose phosphate isomeraseGluG-6-PF-6-PF-1,6-2PATPADPATPADP1,3-diphospho-glycerate3-phospho-glycerate2-phosphoglyceratepyruvateDihydroxyacetone phosphateGlyceraldehyde 3-phosphateNAD+NADH+H+ADPATPADPATPPhosphoenolpyruvatedih

16、ydroxyacetone phosphateglyceraldehyde 3-phosphateOne molecule of glucose is converted to two molecules of glyceraldehyde 3-phosphate ，which consumes two ATPThe following steps can be regarded as the reaction of two glyceraldehyde 3-phosphate oxygenation of glyceraldehyde 3-phosphate to 1,3-diphospho

17、-glyceratePi、NAD+ NADH+H+ Glyceraldehyde3 phosphate dehydrogenaseGluG-6-PF-6-PF-1,6-2PATPADPATPADP1,3-diphospho-glycerate3-phospho-glycerate2-phosphoglyceratepyruvateDihydroxyacetone phosphateGlyceraldehyde 3-phosphateNAD+NADH+H+ADPATPADPATPPhosphoenolpyruvateThe only dehydrogenation reaction in Gly

18、colysis1,3-BPG is high-energy compound PO32-Glyceraldehyde 3-phosphate1,3-diphospho-glycerate(1,3-BPG) The conversion of diphosphoglycerate to 3-phosphoglycerateADP ATP Phosphoglycerate kinaseGluG-6-PF-6-PF-1,6-2PATPADPATPADP1,3-diphospho-glycerate3-phospho-glycerate2-phosphoglyceratepyruvateDihydro

19、xyacetone phosphateGlyceraldehyde 3-phosphateNAD+NADH+H+ADPATPADPATPPhosphoenolpyruvate 1st substrate-level phosphorylationOPO32-diphosphoglycerate(1,3-BPG)3-phosphoglycerate The conversion of 3-phospho-glycerate to 2-phosphoglyceratePhosphoglycerate mutaseGluG-6-PF-6-PF-1,6-2PATPADPATPADP1,3-diphos

20、pho-glycerate3-phospho-glycerate2-phosphoglyceratepyruvateDihydroxyacetone phosphateGlyceraldehyde 3-phosphateNAD+NADH+H+ADPATPADPATPPhosphoenolpyruvate3-phospho-glycerate2-phosphoglycerate The conversion of 2-phosphoglycerate to phosphoenolpyruvateenolase(Mg2+/Mn2+ )GluG-6-PF-6-PF-1,6-2PATPADPATPAD

21、P1,3-diphospho-glycerate3-phospho-glycerate2-phosphoglyceratepyruvateDihydroxyacetone phosphateGlyceraldehyde 3-phosphateNAD+NADH+H+ADPATPADPATPPhosphoenolpyruvatePEP is a high energy compound2-phosphoglycerate phosphoenolpyruvateH2OADP ATP K+ Mg2+Pyruvate kinaseGluG-6-PF-6-PF-1,6-2PATPADPATPADP1,3-

22、diphospho-glycerate3-phospho-glycerate2-phosphoglyceratepyruvateDihydroxyacetone phosphateGlyceraldehyde 3-phosphateNAD+NADH+H+ADPATPADPATPPhosphoenolpyruvate The conversion of Phosphoenolpyruvate to pyruvate2nd substrate-level phosphorylation Phosphoenolpyruvateenolpyruvatepyruvate (二) The conversi

23、on of two molecules of pyruvate to two molecules of lactate pyruvatelactateNADH+H+ may come from dehydrogenation of Glyceraldehyde 3-phosphateLactate dehydrogenase (LDH) NADH + H+ NAD+ E1: hexokinase E2: phosphofructokinaseE3: Pyruvate kinaseNAD+ lactateGluG-6-PF-6-PF-1, 6-2PATP ADP ATPADP1,3-diphos

24、phoglycerate3-phospho-glycerate2-phosphoglyceratepyruvateDihydroxyacetone phosphateGlyceraldehyde 3-phosphateNAD+ NADH+H+ ADP ATP ADP ATPphosphoenolpyruvateE2E1E3NADH+H+ Summary of glycolysis reaction site：cytosol Glycolysis is an anaerobic process including three unreverse reactions G G-6-P ATP ADP

25、 hexokinaseATP ADP F-6-P F-1,6-2P phosphofructokinaseADP ATP PEP pyruvatePyruvate kinase The form and numbers of energy production form：substrate-level phosphorylation Pure numbers of ATP：One molecule of glucose 22-2= 2ATPOne glucose unit from glycogen 22-1= 3ATP fates of lactate Used by degradation

26、Lactate cycle（gluconeogenesis ）fructosehexokinaseGluG-6-PF-6-PF-1,6-2PATPADPATPADPpyruvategalactoseGalactose-1-PGlucose-1-PkinaseisomeraseMannose Mannose -6-PhexokinaseisomeraseOther hexoses can enter into glycolysis二、regulation of glycolysisKey enzymes hexokinase phosphofructokinase Pyruvate kinase

27、Forms allosteric regulation covalent modification （一） 6- phosphofructokinase -1(PFK-1) * allosteric regulation allosteric activator ： F-2,6-2P; AMP; ADP; F-1,6-2P; allosteric inhibitor：citric acid ; ATP F-1,6-2P activated by positive feed back AMP、ATP compete the allosteric site outside of the activ

28、ation centerF-6-P F-1,6-2P ATP ADP PFK-1PP2BPi PKA ATP ADP Pi GlucagonATP cAMP activationF-2,6-2P +/+AMP +citric acidAMP +citric acidPFK-2（with activation）FBP-2（without activation）6-PFK-2 PFK-2（ without activation ）FBP-2（ with activation ）PPFructose Bisphosphatase -2 （二） Pyruvate kinase1. allosteric

29、 regulation allosteric inhibitor：ATP, Alanine allosteric activator ： fructose-1,6-diphosphate2. Regulation of covalent modification Pyruvate kinasePyruvate kinaseATP ADP Pi phosphoprotein phosphatase（without activaiton） （with activation） GlucagonPKA, CaM kinasePPKA：protein kinase ACaM：Calmodulin (三)

30、 hexokinase or glucose kinase* Glucose-6-phosphate has feedback inhibition on hexokiase ，but has no effect on glucose kinase in liver* Long-chain acyl-CoA esters has allosteric inhibition on glucose kinase in liver 三、 Physiologic role of glycolysisThe effective way of energy production under anaerob

31、ic conditions2. The important energy production pathway under anaerobic conditions in some cells Cells without mitochondria：red blood cells cells with active metabolism ：white blood cells , bone marrow cellsSection III Aerobic Oxidation of CarbohydrateReaction site ： cytosol and mitochondriaconcept:

32、 when oxygen is enough，glucose oxidation is processing completely to produce H2O and CO2，and to release energy.The Process of Aerobic Oxidation of CarbohydratesStage 1 ：glycolysis pathwayStage 2： oxidative decarxylation of pyruvateStage 3：TAC cycle G（Gn） Stage 4：oxidative phosphorylationpyruvateacet

33、yl CoA CO2 NADH+H+ FADH2H2O O ATP ADP TAC cycle cytosolmitochondria（一）oxidative decarboxylation of pyruvatepyruvateacetyl CoA NAD+ , HSCoA CO2 , NADH + H+ Pyruvate Dehydrogenase complexComponents of Pyruvate Dehydrogenase complex enzymeE1： Pyruvate Dehydrogenase E2：Dehydrolipoyl Transacetylase E3：De

34、hydrolipoyl DehydrogenaseHSCoANAD+ co-enzyme TPP Lipoic acid（ ) HSCoA FAD, NAD+SSLCO2 CoASHNAD+NADH+H+5. NADH+H+的生成1. -羥乙基-TPP的生成 2.乙酰硫辛酰胺的生成 3.乙酰CoA的生成4. 硫辛酰胺的生成 TAC、citric acid cycle、Krebs cycle（二） Tricarboxylic acid Cycle, TAC*introductionReaction site mitochondriaCoASHNADH+H+NAD+CO2NAD+NADH+H+CO

35、2GTPGDP+PiFADFADH2NADH+H+NAD+H2OH2OH2OCoASHCoASHH2O Citrate synthaseaconitase Isocitrate dehydrogenase -ketoglutaratedehydrogenase complexsuccinyl-CoA synthetase Succinate dehydrogenasefumuraseMalate dehydrogenaseGTPGDPATPADPAMP kinase Synthesis of citrate ：un-reverse reaction O=C-COOH CH3 CH2COOH C

36、H2 + C=O HO-C-COO- COOH SCoA CH2COOHOxaloacetate acetyl CoA citrateCitrate synthaseH2OCoA-SHUn-reverse reaction synthesis of isocitrate COO- COO- COO- CH2 CH H-C-OH- OOC-C-OH - OOC-C - OOC-C-H CH2 CH2 CH2 COO- COO- COO- Citrate cis-Aconitate isocitrate H2OH2O 1st oxidative decarboxylation to form-ke

37、toglutarate： COO- COO- H-C-OH C=O -OOC-C-H CH2 CH2 CH2 COO- COO- isocitrate -ketoglutarateIsocitrate dehydrogenase NAD+NADH+H+CO2Mg2+Un-reverse reaction 1st oxidative decarboxylation to form succinyl-CoA: COO- O=CSCoA C=O CH2 CH2 CH2 CH2 COO- COO-ketoglutarate succinyl-CoA high energy compound-ketog

38、lutarate dehydrogenase complexNAD+CoA-SHNADH+H+CO2Un-reverse reactionsubstrate-level phosphorylation：catalysed by succinyl-CoA synthetaseO=CSCoA COO- CH2 CH2 CH2 CH2 COO- COO-succinyl-CoA succinateThe only substrate-level phosphorylation in TAC to produce GTPsuccinyl-CoA synthetaseGDP+PiGTP+CoA dehy

39、drogenation of succinate to form fumarate: CH2-COO- HC-COO- CH2-COO- -OOC-C-H Succinate fumarate Succinate dehydrogenaseFADFADH2 Formation of malate： HC-COO- HO-CH-COO- -OOC-C-H CH2-COO- fumarate malate fumuraseH2O Formation of Oxaloacetate： HO-CH-COO- O=C-COOH CH2-COO- CH2-COO- Malate Oxaloacetate

40、MalatedehydrogenaseNAD+NADH+H+ Summary of TAC Concept of TAC：Acetyl-CoA+Oxaloacetatecitrate repeat dehydrogenation and decarboxylation Oxaloacetate. Acetyl-CoA is oxidated.the reaction is located in mitochondria Points of TAC cycleFour times of dehydrogenation ，three un-reverse reaction, two times o

41、f decarboxylation ，one time of substrate-level phosphorylationAfter TAC cycle, one molecular of acetyl-CoA forms：1 FADH2，3 NADH+H+，2 CO2， 1 GTP. Total: 12ATP 。Key enzymes： Citrate synthase -ketoglutaratedehydrogenase complex Isocitrate dehydrogenase the reaction cycle can not be reversed TCA Cycle I

42、ntermediates act as catalyzer without change of amountOxaloacetate and other TAC cycle Intermediates can not be synthesized directly from acetyl-CoAIntermediates can not be directly oxidated in TAC cycle to form CO2 and H2O Role of TCA Cycle Intermediates ：Some of the Cycle Intermediates can be conv

43、erted to other materials, for example：Oxaloacetateaspartate-ketoglutarateGlutaminecitrateFatty acid Succinyl CoA porphyrin When sugar supply is not enough，malate、oxaloacetatepyruvateacetyl-CoA TAC，the absence of oxaloacetate can course TAC obstacle oxaloacetateoxaloacetate decarboxyase Pyruvate CO2

44、malate蘋果酸酶 Pyruvate CO2 NAD+ NADH + H+ * Recruit of oxaloacetate ： oxaloacetatecitrateCitratelyaseAcetyl-CoA pyruvatePyruvatecarboxylase CO2 malateMalatedehydrogenaseNADH+H+ NAD+ aspartateglutamineoxaloacetic transaminase -ketoglutarateglutamine2. Physiological significance of TAC cycle The common p

45、athway of oxidative degradation of three major nutrientsThe hinge linked the metabolism of three major nutrientsProviding small precursor molecules for metabolsim of other substancesProcviding H+ + e for respiratory chainH+ + e enter into respiratory chain where they can be oxidation completely to p

46、roduce H2O, coupled with oxidative phosphorylation to form ATP from ADPNADH+H+ H2O、3ATP O H2O、2ATP FADH2 O 二、 Aerobic Oxidation to create ATP 1mol glucoseStage I： 2（3）2+4-2=6（8）Stage II： 3 2=6Stage III：122=24Tptal =36（38） mol The physiological significance of Aerobic OxidationThe most major pathway

47、to provide energy in most tissues of the human beings三、regulation of Aerobic Oxidation glycolysis： hexokinase oxidative decarboxylation of pyruvate ：Pyruvate Dehydrogenase complex TAC cycle：citrate synthase Pyruvate kinase 6- phosphofructokinase -1-ketoglutarate dehydrogenase complexIsocitrate dehyd

48、rogenaseKey enzymes1. Pyruvate Dehydrogenase complex allosteric regulationallosteric inhibitor ：Acetyl-CoA; NADH; ATP allosteric activator ：AMP; ADP; NAD+ * Acetyl-CoA/HSCoA or NADH/NAD+，inhibit Regulation of covalent modification 目 錄pyruvateAcetyl-CoA citrateoxaloacetateSuccinyl CoA -ketoglutaratei

49、socitratemalate NADH FADH2 GTP ATP Isocitrate dehydrogenaseCitrate synthase-ketoglutarate dehydrogenase complexATP +ADP ADP +ATP citrateSuccinyl-CoA NADH Succinyl-CoA NADH +Ca2+ Ca2+ ATP、ADP inhibition by production accumulation allosteric feedback inhibition by Intermediates others, esp:Ca2+ can ac

50、tivate many enzymes2. Regulation of TAC cycleCharacteristics of regulation of Aerobic Oxidation Regulation by key enzymes Regulation by ATP/ADP or ATP/AMP ratio through the whole process TAC cycle affected by the speed of oxidative phosphorylation harmony regulation between TAC cycle and glycolysis

51、pathway . glycolysis pathway which provides pyruvate to form acetyl-CoA is dependent on the need of TAC cycle.2ADP ATP+AMP Adenylate Kinase The concentration of ATP in the body is 50-fold more than AMP. After the above reaction，the change of ATP/AMP is larger than that of ATP, which leads to signal

52、amplification Regulation by ATP/ADP or ATP/AMP ration， the influence by ATP/AMP is more notable四、Pastuer effect：* concept：the phenomenon of glycolysis inhibition by Aerobic Oxidation* mechanism In the presence of oxygen，NADH+H+e enter into the mitochondria to be oxidation and the conversion of pyruv

53、ate to lactate is suppressed.In the Absence of oxygen，glycolysis pathway is enhanced，the concentration of NADH+H+ in cytosol increases and pyruvate is converted to lactate as hydrogen acceptorSection VIPentose Phosphate Pathway* concept：磷酸戊糖途徑是指由葡萄糖生成磷酸戊糖及NADPH+H+，前者再進一步轉變成3-磷酸甘油醛和6-磷酸果糖的反應過程。* Site

54、 ：cytosolStage I：oxidative reaction To form Pentose Phosphate ， NADPH+H+ and CO2一、the process of Pentose Phosphate pathway* The reaction includes two stages Stage II：group transfer reaction6-磷酸葡萄糖酸 5-磷酸核酮糖 NADPH+H+ NADP+ H2O NADP+ CO2 NADPH+H+ 6-磷酸葡萄糖脫氫酶6-磷酸葡萄糖酸脫氫酶 HCOHCH2OH CO Glucose-6-phosphate6-

55、磷酸葡萄糖酸內酯 1. The formation of Pentose Phosphate 5-磷酸核糖 6-磷酸葡萄糖脫氫酶是關鍵酶。兩次脫氫生成NADPH + H+。磷酸核糖是非常重要的中間產物。G-6-P 5-磷酸核糖 NADP+ NADPH+H+ NADP+ NADPH+H+ CO2 磷酸戊糖通過3C、4C、6C、7C等演變，最終生成3-磷酸甘油醛和6-磷酸果糖。3-磷酸甘油醛和6-磷酸果糖，可進入酵解途徑。2. 基團轉移反應 5-磷酸核酮糖(C5) 3 5-磷酸核糖 C55-磷酸木酮糖 C55-磷酸木酮糖 C57-磷酸景天糖 C73-磷酸甘油醛 C34-磷酸赤蘚糖 C46-磷酸果糖

56、 C66-磷酸果糖 C63-磷酸甘油醛 C3磷酸戊糖途徑第一階段 第二階段 5-磷酸木酮糖 C55-磷酸木酮糖 C57-磷酸景天糖 C73-磷酸甘油醛 C34-磷酸赤蘚糖 C46-磷酸果糖 C66-磷酸果糖 C63-磷酸甘油醛 C36-磷酸葡萄糖(C6)3 6-磷酸葡萄糖酸內酯(C6)3 6-磷酸葡萄糖酸(C6)3 5-磷酸核酮糖(C5) 3 5-磷酸核糖 C53NADP+ 3NADP+3H+ 6-磷酸葡萄糖脫氫酶 3NADP+ 3NADP+3H+ 6-磷酸葡萄糖酸脫氫酶 CO2總反應式 ： 36-磷酸葡萄糖 + 6 NADP+ 26-磷酸果糖+3-磷酸甘油醛+6NADPH+H+3CO2 磷酸

57、戊糖途徑的特點 生成NADPH+H+生成5-磷酸核糖3、4、5、6、7碳糖的演變二、磷酸戊糖途徑的調節 * 6-磷酸葡萄糖脫氫酶是關鍵酶* NADPH/NADP+比值升高抑制， 降低激活。 三、磷酸戊糖途徑的生理意義（一）為核苷酸的生成提供核糖 （二）提供NADPH作為供氫體參與多種代謝反應 1. NADPH是體內許多合成代謝的供氫體 2. NADPH參與體內的羥化反應，與生物合成或生物轉化有關3. NADPH可維持GSH的還原性 2G-SH G-S-S-GNADP+ NADPH+H+A AH2 Section V Glycogenesis and Glycogenolysis糖原儲存的主要器

58、官及其生理意義肌糖原，180 300g，為肌肉收縮氧化供能肝糖原，70 100g，維持血糖水平 1. 葡萄糖單元以-1,4-糖苷 鍵形成長鏈。2. 約10個葡萄糖單元處形成分枝，分枝處葡萄糖以-1,6-糖苷鍵連接，分支增加，溶解度增加。3. 每條鏈都終止于一個非還原端.非還原端增多，以利于其被酶分解。糖原的結構特點及其意義 目 錄一、糖原的合成代謝 （二）合成部位（一）定義糖原的合成(glycogenesis) 指由葡萄糖合成糖原的過程。肝、肌肉細胞胞漿葡萄糖6-磷酸葡萄糖1-磷酸葡萄糖變位酶UDPGUDPG焦磷酸化酶UTPPPiOCH2OHpp尿苷糖原n糖原n+1 + UDP 糖原合酶（三）

59、糖原合成途徑 1. 葡萄糖磷酸化生成6-磷酸葡萄糖葡萄糖 6-磷酸葡萄糖 ATP ADP 己糖激酶;葡萄糖激酶（肝） 1-磷酸葡萄糖 磷酸葡萄糖變位酶 6-磷酸葡萄糖 2. 6-磷酸葡萄糖轉變成1-磷酸葡萄糖 +UTP 尿苷 PPPPPi UDPG焦磷酸化酶 3. 1- 磷酸葡萄糖轉變成尿苷二磷酸葡萄糖 1- 磷酸葡萄糖 尿苷二磷酸葡萄糖 UDPG 糖原n + UDPG 糖原n+1 + UDP 糖原合酶UDP UTP ADP ATP 核苷二磷酸激酶4. -1,4-糖苷鍵式結合糖鏈延長 糖原n：較小糖原分子，糖原引物，UDPG 上葡萄糖基的接受體。 糖原合酶催化糖原糖鏈末端延長：糖原合酶pp尿苷

60、pp尿苷糖原（n）糖原（n+1）反應反復進行，糖鏈不斷延長。5.糖原分枝的形成 分 支 酶 -1,6-糖苷鍵 -1,4-糖苷鍵 當糖鏈長度達到12 18個葡萄糖基時轉移67個葡萄糖基近來人們在糖原分子的核心發現了一種名為glycogenin的蛋白質。Glycogenin可對其自身進行共價修飾，將UDP-葡萄糖分子的C1結合到其酶分子的酪氨酸殘基上，從而使它糖基化。這個結合上去的葡萄糖分子即成為糖原合成時的引物。作為引物的第一個糖原分子從何而來？ 二、糖原的分解代謝 * 定義* 肝糖元的分解 糖原分解 (glycogenolysis )習慣上指肝糖原分解成為葡萄糖的過程。糖原（n）糖原（n-1）