高中生物奥赛辅导生化——糖代谢

1、生物化学 淀粉酶淀粉酶纤维素酶纤维素酶半纤维素酶半纤维素酶果胶酶果胶酶a a- -淀粉酶淀粉酶b-b-淀粉酶淀粉酶葡萄糖淀粉酶葡萄糖淀粉酶异淀粉酶异淀粉酶麦芽糖酶麦芽糖酶蔗糖酶蔗糖酶乳糖酶乳糖酶1.1 糖类水解酶1.2 糖类在人体中的消化糖类食物糖类食物唾液淀粉酶唾液淀粉酶咀嚼、部分水解咀嚼、部分水解HCl有限水解有限水解胰淀粉酶胰淀粉酶a a-糊精、麦芽糖和少量葡萄糖糊精、麦芽糖和少量葡萄糖糖苷酶糖苷酶单糖单糖吸收吸收 糖的吸收就是指游离的葡萄糖（单糖）进入糖的吸收就是指游离的葡萄糖（单糖）进入到生物体内（细胞内）的过程。到生物体内（细胞内）的过程。糖的吸收方式糖的吸收方式主动运输主动运输促

2、进扩散促进扩散基团转位基团转位1.3 糖的吸收血糖血糖80120 mg/100 ml4070， 120180低低 高高血糖的来源、去向u Glucose is very soluble source of quick and ready energy.u It is a relatively stable and easily transported.u Glucose is the only source of energy in red blood cells酵解（酵解（glycolysis): 是酶将是酶将葡萄糖葡萄糖降解成降解成丙酮酸丙酮酸并伴随着并伴随着生成生成ATP的过程。它是动物

3、、植物、的过程。它是动物、植物、微生物细胞中葡萄糖分解产生能量的微生物细胞中葡萄糖分解产生能量的共同代共同代谢谢途径。途径。发酵（发酵（fermentation)：厌氧有机体把酵解生成厌氧有机体把酵解生成的的NADH中的氢交给中的氢交给丙酮酸，生成乳酸；丙酮酸，生成乳酸；或或丙酮酸脱羧生成的丙酮酸脱羧生成的乙醛，生成乙醇乙醛，生成乙醇。2.1 概念 Glycolysis 糖酵解是葡萄糖生成丙酮酸的代谢途径糖酵解是葡萄糖生成丙酮酸的代谢途径糖酵解概况丙酮酸丙酮酸Anaerobic conditionsAerobic conditionsExercising muscleYeastThe fate

4、 of glucose is varies with physiological conditions, tissues, and organisms.葡萄糖葡萄糖2. 糖酵解是无氧条件下的反糖酵解是无氧条件下的反应应(fermentations);3. 糖酵解发生的部位是糖酵解发生的部位是细胞质细胞质；2.2.2 糖酵解概况Preparatary phasePayoff phase(产能产能)22 ATP2.2.2 糖酵解概况4糖酵解途径包括两个阶段糖酵解途径包括两个阶段(耗能耗能) 2ATPNet: 2 ATP； a limited amount5. 中间代谢产物是磷酸化的中间代谢产物是磷

5、酸化的;6. 化学变化的三种类型；化学变化的三种类型；7. 糖酵解是严密调控的糖酵解是严密调控的.碳原子途径碳原子途径磷酸途径磷酸途径氧化还原反应的电子途径氧化还原反应的电子途径2.2.2 糖酵解概况2.2.2 糖酵解概况Glucose is phosphorylated. The negative charge concentrates glucose in the cell and glucose becomes less stable. (P ，C ，e )2.2.2 糖酵解概况8. Types of reactions occurring in glycolysisPhosphoryl

6、 group transfer: kinase(激酶激酶);磷酸化酶磷酸化酶+ATPRROHO-POOO-+ADP+H+KinaseABCD激酶激酶2.2.2 糖酵解概况8. Types of reactions occurring in glycolysisPhosphoryl group shift: mutase（变位酶）（变位酶）RCMutaseO HHC H2O-POOO-RCOHC H2OHO-PO-OPhosphoryl shift. A phosphoryl group is shifted from one oxygen atom to another within a mo

7、lecule by a mutase.2.2.2 糖酵解概况8. Types of reactions occurring in glycolysisIsomerization: isomerase(异构酶异构酶);RIsomeraseCCH2OHORCCOHHOHIsomerization. A ketose (酮糖） is converted into an aldose （醛醣）, or vice versa, by an isomerase.2.2.2 糖酵解概况8. Types of reactions occurring in glycolysisDehydration: dehy

8、dratase（enolase, 烯醇化酶）烯醇化酶）Dehydration. A molecule of water is eliminated by a dehydratase.HDehydrataseCCO HHHHCCH+H2O2.2.2 糖酵解概况8. Types of reactions occurring in glycolysisAldol cleavage: aldolase（醛缩酶）（醛缩酶）Aldol cleavage. A carbon-carbon bond is split in a reversal of an aldol condensation by an a

9、ldolase.RAldolaseCCOHHCHOHRORCCOHCHOHROH Phosphoryl group transfer: kinase; Phosphoryl group shift: mutase（变位酶）（变位酶）; Isomerization: isomerase; Dehydrogenation: dehydrogenase（脱氢酶）（脱氢酶）; Dehydration: dehydratase (enolase，烯醇化酶，烯醇化酶); Aldol cleavage: aldolase（醛缩酶）（醛缩酶）.糖酵解概况Preparatory phase:Phosphoryl

10、ation of glucose and its conversion to glyceraldehyde-3-phosphatePayoff phaseConversion of glyceraldehyde-3-phosphate to pyruvate and the coupled formation of ATP2.2.3 糖酵解的反应葡萄糖葡萄糖葡萄糖葡萄糖-6-磷酸磷酸果糖果糖-6-磷酸磷酸果糖果糖-1,6-二磷酸二磷酸甘油醛甘油醛-3-磷酸磷酸二羟丙酮磷酸二羟丙酮磷酸甘油醛甘油醛-3-磷酸磷酸二羟丙酮磷酸二羟丙酮磷酸1,3-二磷酸甘油酸二磷酸甘油酸 3-磷酸甘油酸磷酸甘油酸 2

11、-磷酸甘油酸磷酸甘油酸磷酸烯醇式丙酮酸磷酸烯醇式丙酮酸丙酮酸丙酮酸 带有负电荷的磷酸基团使中间产物具有极性，从而使这些产物不易透过脂膜而失散。 磷酸基团在各反应步骤中，对酶来说，起到信号基团的作用，有利于与酶结合而被催化。 磷酸基团经酵解作用后，最终形成ATP的末端磷酸基团，因此具有保存能量的作用。Intermediary metabolites are phosphated（磷酸化的）(1) Glucose is Phosphorylated First to Enter GlycolysisG= -4.0 kcal mol-1Hexokinase己糖激酶(1) Glucose is Pho

12、sphorylated First to Enter Glycolysis己糖激酶与葡萄糖结合时的构象变化己糖激酶与葡萄糖结合时的构象变化(2) Glucose-6-P Isomerizes from an Aldose to a Ketose G= 0.40 kcal/molPhosphoglucose Isomerase磷酸葡萄糖同分异构酶(2) Glucose-6-P Isomerizes from an Aldose to a Ketose Phosphoglucose IsomeraseThe enzyme opens the ring, catalyzes the isomeriz

13、ation, and promotes the closure of the five member ring. (3) Fructose-6-P is Further Activated by PhosphorylationPhosphofructokinasePFK（磷酸果糖激酶）G= -3.4 kcal mol-1The 2nd investment of an ATP in glycolysis. 磷酸果糖激酶是一种变构酶，糖酵解的速率糖酵解的速率严格地依赖该酶的活力水平，它是哺乳动物糖酵解途径最重要的调控关键酶调控关键酶。 肝中PFK受高浓度的ATP的抑制。ATP结合于调节部位结合于

14、调节部位。ATP对该酶的别构抑制效应可被AMP解除。因此ATP/AMP的比例关系对此酶有明显的调节作用。(3) Fructose-6-P is Further Activated by Phosphorylation(4) Fructose-1,6-Bisphosphate is Cleaved (lysed) in the MiddleAldolase (醛缩酶）G= 5.7 kcal mol-1Reverse aldol condensation; converts a 6 carbon atom sugar to 2 molecules, each containing 3 carbon

15、 atoms.果糖果糖-1，6-二磷酸二磷酸FBP二羟丙酮磷酸二羟丙酮磷酸（DHAP）甘油醛甘油醛-3-磷酸磷酸（GAP）(5) Triose phosphate InterconvertTriose phosphate isomerase丙糖磷酸异构酶 ，TIM二羟丙酮磷酸二羟丙酮磷酸（DHAP）甘油醛甘油醛-3-磷酸磷酸（GAP）G = 1.8 kcal mol-1甘油醛甘油醛-3-磷酸磷酸(5) Triose phosphate InterconvertAll the DHAP is converted to glyceraldehyde 3-phosphate（GAP）. Althou

16、gh, the reaction is reversible it is shifted to the right since glyceraldehyde 3-phosphate is a substrate for the next reactions of glycolysis. Thus, both 3-carbon fragments are subsequently oxidized.(5) Triose phosphate Interconvert二羟丙酮磷酸二羟丙酮磷酸（DHAP）甘油醛甘油醛-3-磷酸磷酸（GAP）单烯二羟负单烯二羟负离子中间体离子中间体G = 1.8 kca

17、l mol-1(6) Glyceraldehyde-3-phosphate is OxidizedGlyceraldehyde 3-phosphate DH甘油醛甘油醛-3-磷酸脱氢酶，磷酸脱氢酶，GAPDHThe energy yielding phaseG = 1.5 kcal mol-11，3二二磷酸甘磷酸甘油酸油酸(6) Glyceraldehyde-3-phosphate is OxidizedGAPDH碘乙酸碘乙酸无活性的酶无活性的酶甘油醛-3-磷酸脱氢酶 甘油醛-3-磷酸脱氢酶（GAPDH）能够利用砷酸砷酸代替磷酸磷酸参加反应，生成3-P-甘油酰砷酸甘油酰砷酸，这是一个高度不稳定

18、的化合物， 在水溶液中，可立刻自发地分解为3-P-甘油酸和砷酸甘油酸和砷酸。 因此，砷酸不抑制糖酵解的继续进行砷酸不抑制糖酵解的继续进行，但它不它不能产生高能磷酸键能产生高能磷酸键。所以，砷酸是糖酵解中基质水平磷酸化的解偶联剂解偶联剂。(7) The anhydride phosphate in 1,3-BPG is used to generate ATPPhosphoglycerate Kinase （磷酸甘油酸激酶，PGK）Substrate-level phosphorylation （ 底物水平的磷酸化）G = -4.5 kcal mol-1Remember: 2 molecules

19、 of ATP are produced per glucose.1，3-二磷酸甘油酸二磷酸甘油酸3-磷酸甘油酸磷酸甘油酸u Mutase belongs to the isomerase family.(8) Phosphate reversibly shifts between C2 and C3 on glyceratePhosphate shiftPhosphoglycerate mutase磷酸甘油酸变位酶G = 1.1 kcal mol-13-磷酸甘油酸磷酸甘油酸2-磷酸甘油酸磷酸甘油酸 磷酸烯醇式丙酮酸，PEP has high phosphoryl group transfer

20、 potential （高基团转移势能）.(9) The Phosphoryl Group Transfer Potential is Markedly Elevated by DehydrationEnolase（烯醇化酶）G = 0.4 kcal mol-1Dehydration reaction(10) The Phosphate Group on PEP is Transferred to ADPPyruvate Kinase，丙酮酸激酶G = -7.5 kcal mol-1烯醇式烯醇式酮式酮式2nd example of substrate level phosphorylation

21、 （底物水平磷酸化）. The net yield from glycolysis （酵解） is 2 ATP.Substrate level phosphorylcation is the synthesis of ATP from ADP that is not linked to the electron transport system（电子传递系统）.PEP+ADPPyr+ATP(10) The Phosphate Group on PEP is Transferred to ADP红血球红血球标准态标准态Summary: G at each step of GlycolysisGl

22、ucosePyruvateGlucose + 2 Pi + 2 ADP + 2 NAD+ 2 pyruvate + 2 ATP + 2 NADH +2 H+The Energy released from the anaerobic conversion of glucose to pyruvate is -47 kcal mol-1. Under aerobic conditions much more chemical bond energy can be extracted from pyruvate.The question still remains: How is NAD+ sup

23、plied under anaerobic conditions? Or how is redox balance maintained?Summary: The Conversion of Glucose to Pyruvate2.2.4 丙酮酸的代谢去路lPyruvate reduced (还原) and NAD+ regenerated (生成);lCatalyzed by lactate dehydrogenase (乳酸脱氢酶);lThis happens in animal tissues when O2 is limited;lThis also happens in many

24、microorganisms (e.g., lactobacilli).(1) Pyruvate is the final electron acceptor in lactic acid fermentationWhat happens to the lactate after a run?uPyruvate decarboxylase 丙酮酸脱羧酶 (present only in those alcohol fermentative organisms) and alcohol dehydrogenase 乙醇脱氢酶 (present in many organisms includin

25、g human) catalyzes the two-step reactions.G0 = -10.46 kJ/mol(2) Acetaldehyde is the final electron acceptor in alcohol fermentationRemember! 酵解过程必须提供NAD+，而缺氧的情况下, NADH不能够把H传递给电子传递链而产生NAD+；NADH的H可以选择传递给产物从而使酵解过程得以进行从而产生能量。l碳原子途径（碳骨架的去向）碳原子途径（碳骨架的去向）:Glucose(6C)2pyruvate(3C)n磷原子途径磷原子途径 (ATP的变化的变化):消耗消

26、耗G6P 的形成的形成 1FBP的形成的形成 1产生产生1,3-二磷酸甘油酸的形成二磷酸甘油酸的形成 + 2PEP的形成的形成 + 2u氧化还原反应的电子途径氧化还原反应的电子途径:1,3-二磷酸甘油酸的形成二磷酸甘油酸的形成终产物终产物2 NADH + H+2.2.5 Overal balance of glycolysis2.2.6 Regulation of the Glycolytic pathwaynEnzyme reactions that have a significant negative G are often control sites.nIN glycolysis:nH

27、exokinase nPhosphofuctokinase(PFK)nPyruvate Kinaseare regulatory enzymes.nPFK is the most important. 磷酸果糖激酶催化的反应是糖酵解的限速反应。High levels of ATP inhibit, increased levels of AMP reverses the action of ATP.Citrate(柠檬酸） also inhibits PFK. High levels of citrate indicates that the cell is rich in biosynthe

28、tic precursors（生物合成前导物） emanating from the pathway. PFK is an allosteric enzyme糖酵解作用不仅是提供能量，也为生物合成提供碳骨架。糖酵解作用不仅是提供能量，也为生物合成提供碳骨架。 PFK is an allosteric enzyme 酶的可逆变构，磷酸化作用的调节及转录的控制根据不同情况下可在百万之一秒、几秒或几小时内发生变化。. 糖原磷酸解转变为糖原磷酸解转变为1-磷酸葡萄糖进入糖酵解磷酸葡萄糖进入糖酵解n这步反应是磷酸解而不是水解这步反应是磷酸解而不是水解.2.2.7

29、 其它糖进入糖酵解的途径其它糖进入糖酵解的途径2.2.7 其它糖进入糖酵解的途径其它糖进入糖酵解的途径Mutase 变位酶变位酶FructoseFructokinase（激酶）Fructose-1-PFBPFructose-1-P-kinaseFructose-1-P aldolase （醛缩酶）triose kinaseglyceraldehyde-3-phosphate (G3P) Fructose(果糖）果糖）enters glycolysis mainly via F-1-P pathway2.2.7 其它糖进入糖酵解的途径其它糖进入糖酵解的途径肝脏肝脏肌肉肌肉2.2.7

30、.4 Galactose （半乳糖）（半乳糖） enters glycolysis pathway via the galactose-glucose interconversion pathway （p87-88）GalactoseGalactose-1-phosphateUDP-GlucoseUDP-GalactoseGlucose-1-phosphateGlucose-6-phosphateUDP-4-keto-GlucosenIn adults:尿苷酰转移酶尿苷酰转移酶UDP-半乳糖半乳糖-4-差向异构酶差向异构酶UDP-Galactose4-epimeraseUDP-葡萄糖葡萄糖焦磷酸化酶焦磷酸化酶 Galactose enters glycolysis pathway via the galactose-glucose interconversion pathwayGalactoseG