2. Chapter 4 Carbohydrate Metabolism 牛永东

3. 生物化学的学习方法 特点一：与数理化不同，尚未进入定量科 学的阶段，还处在定性科学阶段。因此不可能 通过公式或定理推出一个准确的结论 特点二： 是没有绝对，几乎所有的结论 都可以被一些例外打破（生物多样性） 一般性结论：生物化学的学习应以概念 为主 --- 以记忆为主，在记忆的基础上加以理解

4. 【目的与要求】 掌握糖酵解 glycolysis 、有氧氧化、巴斯德效应 Pastuer effect 、磷酸戊糖途径 、磷酸戊糖途径、糖异生 gluconeogenesis 、乳酸循环 Cori cycle 等概念 …… 掌握糖酵解、有氧氧化 (TCA cycle) 、磷酸戊糖途径、糖异 生、糖原合成 glycogenesis 与分解 glycogenolysis 的细胞定 位、过程、关键酶、调节及意义 …… 掌握血糖的来源和去路及其调节 ……

5. outline Introduction Glycolysis (Anaerobic Degradation) Aerobic oxidation of glucose The Pentose Phosphate Pathway Glycogen Formation and Degradation Gluconeogenesis

6. Definition of Metabolism Metabolism (Greek for change) : all the chemical and physical processes that take place in the body * Synthesis (anabolism):  Glucose – Glycogen  FA+ Glycerol – TG  Amino Acids – Protein  Requires Energy Macromolecules Small molecules ANABOLISM CATABOLIS M * Breakdown (catabolism):  Glycogen – Glucose  TG – Fatty Acids + Glycerol  Protein – Amino Acids  Energy is released

7. 1. What are Carbohydrates? Carbohydrates are aldehyde or ketone compounds with multiple hydroxyl groups Empirical formula = (CH 2 O)n, literally a “carbon hydrate” CHO make up 3% of the body’s organic matter

8. Functions of CHO Energy Source (Energy Source (66.8 kJ/1g carbohydrate ) Structural elements Component of nucleic acids Conversion to lipids and non-essential amino acids …….

9. Categories of Carbohydrates Monosaccharides (Single sugar units): the smallest carbohydrates,serve as fuel and carbon sources Disaccharides (formed from 2 monosaccharides joined by a glycoside linkage) Polysaccharides: many monosaccharide units (starch, cellulose)

10. Monosaccharides C 6 H 12 O 6Glucose ( C 6 H 12 O 6 ) -found in fruits, vegetables, honey -“blood sugar” -used for energy Fructose - Found in fruits, honey, corn syrup -“fruit sugar” Galactose - Found as part of lactose in milk CHO Glucose (C 6 H 12 O 6 )

11. Disaccharides Sucrose = glucose + fructose (brown sugar;25% of sugar intake) Lactose = glucose + galactose (milk sugar; least sweet) Maltose = glucose + glucose (honey) Natural Sweetness Natural Sweetness Maltose Sucrose

12. Polysaccharides starch CH 2 OH  -[1-6] linkage  -[1-4] linkages Glucose 1 4 6 O H H H H OH OH HOH OH CH 2 OH

13. Section 1 Digestion Section 1 Digestion of carbohydrates Starch Glycogen Salivary amylase Pancreatic amylase maltose sucrose lactose galactose stomach Brush Border of the Mucosal Epithelium BLOOD glucose fructose galactose glucose fructose Monosaccharides 1 2 3 a -amylase Mouth no significant digestive enzymes present Responsible for most of carbohydrate digestion limited breakdown of starch and glycogen occurs

14. to capillaries Na+ dependent glucose Absorption and transporter,SGLT Lumen of intestine Intestinal Epithelial cell Fructose; also glucose, Glucose Galactose Na + 2K + Na + 3Na + ATP ADP + Pi = facilitated diffusion = Na + -dependent co-transport = Na,K-ATPase GLUT-5 Brush border SGLT-1 Fructose GalactoseGlucose GLUT-2 GalactoseGlucose GalactoseGlucose Na + 2K + 3Na +

15. Family of glucose transporters Name Tissue location K m Comments GLUT1 All mammalian tissues 1mmol/L Basal glucose uptake GLUT2 Liver and pancreatic 15~20mmol/L In the pancreas,plays a role  cells in regulation of insulin In the liver, removes excess glucose from the blood GLUT3 All mammalian tissues 1mmol/L Basal glucose uptake GLUT4 Muscle and fat cells 5mmol/L Amount in muscle plasma membrane increases with endurance training GLUT5 Small intestine － Primarily a fructose transporter

16. : Dietary Fiber Not digested : Dietary Fiber Water insoluble fibers - Cellulose, hemicellulose, pectins （ 果胶 ） …… Water soluble fiber - beans, rice, carrots, fruits…… - Obesity, diabetes, cancer…… Recommended intake of fiber 20-35 g/day; insoluble:soluble = 3:1

17. Anaerobic degradation (glycolysis) glucose Aerobic oxidation Glycogen UDPG G-1-P G-6- P 6-phosphogluconate Fructose 6-p trioses phosphate non-carbohydrates pyruvate acetyl CoAlactate Tricarboxylic acid cycle 2 2 CO+ HO + energy Gluconeogenesis Glycogenesis Glycogenolysis Pentose phosphate pathway P i P i 3. Overview of carbohydrate metabolism

18. Section 2 Glycolysis (Anaerobic Degradation) “Glycolysis” is derived from Greek words glycos (sugar, sweet) and lysis (dissolution) The glycolytic pathway (Glucose to pyruvate) was elucidated by 1940, largely through the pioneering contributions of Gustav Embden.so glycolysis is also known as the Embden-Meyerhof pathway

19. Glycolysis Where in cell ? What are the inputs ? What are the outcomes ? Oxygen required ?

20. Glycolysis （糖酵解） For glycolysis, the overall goal is to break the glucose molecule into smaller, more oxidized pieces 11 steps metabolic pathway to convert 6 carbon glucose into 2 molecules of 3 carbon lactate 乳酸 and two molecules each of and ATP Occurs in cytoplasm has twoglycolysis has two stages: glycolytic pathway ( Glucose to pyruvate ); Fermentation （ 发酵 ） phase ( pyruvate to lactate ) Anaerobic –Does not REQUIRE oxygen –Occurs whether oxygen is available or not

21. breakage of C3-C4 bond glycolytic pathway = breakdown of glucose to yield energy and pyruvate

22. has two glycolytic pathway has two phases A. Energy investment phase (Reactions, 1-5) Glucose(6C) is first phophorylated (thus activated) and then cleaved to produce two glyceraldehyde-3- phosphate(3C) intermediates. 2 ATPs are invested. ( the preparatory phase) B. Energy payoff phase (Reactions 6-10) two glyceraldehyde 3-phosphate intermediates are oxidized, generating to two pyruvate plus four ATP molecules

23. CH 2 O H HO-C-H H-C-OH CHO H-C-OH -P-O O OH C=O CH 2 OH -P-O O OH glucose -P-O O OH isomerase Energy investment phase Step 3. Phosphofructokinase -1 (PFK-1) (2 ATP utilization) Step 1. Hexokinase (1 ATP utilization) Step 2. Phosphoglucose Isomerase (PGI)

24. H C H 2 OH HO-C-H H-C-OH CHO H-C-OH C=O CH 2 OH -P-O O OH -P-O O OH HO-C-H C=O CH 2 O -P-O O OH -P-O O OH CH 2 O H-C-OH + CH 2 OPO 3 = HC=O Glyceraldehyde 3-PO 4 DHAP CH 2 OPO 3 = C=O CH 2 OH dihydroxyacetone phosphate energy investment phase 4. Aldolase

25. isomerase dihydroxyacetone phosphate TPI The isomerization of an aldose to a ketose Glyceraldehyde 3-PO 4 energy investment phase 5. Triose Phosphate Isomerase (TIM or TPI )

26. Glucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1.6-bisphosphate Dihydroxyacetone phosphate Triose phosphate isomerase Aldolase Phosphofructokinase Phosphogluco- isomerase Hexokinase ATPATP ADP ATPATP Glyceraldehyde 3-phosphate energy investment phase Uses 2 ATP

27. CHO H-C-OH CH 2 OPO 3 COO H-C-OH CH 2 OPO 3 C H-C-OH CH 2 OPO 3 ~OPO 3 O PO 4 NAD + NADH + H++ H+ ADP ATP Glyceraldehyde-3-PO 4 dehydrogenase Phosphoglycerate kinase (Reactions, 6-10) Energy payoff phase

28. COO H-C-OH CH 2 OPO 3 3-PGA COO C=O CH 3 Pyruvate COO C~ CH 2 OPO 3 PEP COO H-C-OPO 3 CH 2 OH 2-PGA Low energy High energy -H 2 O ADP ATP Energy payoff phase

29. Glyceraldehyde 3-phosphate NAD + + Pi NADH + H + 1,3-Bisphosphoglycerate Glyceraldehyde 3-phosphate dehydrogenase Phosphoglycerate kinase ADP ATP 3-Phosphoglycerate 2-Phosphoglycerate Phosphoenolpyruvate Pyruvate Pyruvate kinase ADP ATP H2OH2O Enolase Phosphoglyceromutase energy payoff phase ATP generation Oxidation ATP generation

30. Overview of glycolytic pathway

31. Summary of Energy Relationships for glycolytic pathway * Input = 2 ATP 1. glucose + ATP  glucose-6-P 2. fructose-6-P + ATP  fructose 1,6 bisphosphate * Output = 4 ATP + 2 NADH 1. 2 glyceraldehyde-3-P + 2 Pi + 2 NAD+  2 (1,3 bisphosphoglycerate) + 2 NADH 2. 2 (1,3 bisphosphoglycerate) + 2 ADP  2 (3-P-glycerate) + 2 ATP 3. 2 PEP + 2 ADP  2 pyruvate + 2 ATP *Net =2 ATP and 2 NADH

32. Fate of Pyruvate Two anerobic pathways: (Low O 2 ) - to lactate via lactate dehydrogenase in muscle - to ethanol (fermentation) via ethanol dehydrogenase Aerobic pathway – through citric acid cycle and respiration; Enough O 2,this pathway yields far more energy NADH + O 2  NAD+ + energy Pyruvate + O 2  3CO 2 + energyAnaerobicGlycolysis Pyruvate AlcoholFermentation Aerobic Glycolysis Pyruvate Oxygen availability determines fate of Pyruvate

33. The anaerobic fate of Pyruvate ( Reaction 11 of glycolysis ) Hydrogen at C4 of NADH is transferred to the pyruvate uses up all the NADH (reducing equivalents) produced in glycolysis

34. Energy Yield From Glycolysis glucose  6 CO 2 = -2840 kJ/mol 2 ATPs produced = 61 kJ/mol glucose Energy yield = 61/2840 = 2% in all: high investment, low output Overall process of anaerobic glycolysis in muscle can be represented: The lactate, the end product, is exported from the muscle cell and carried by the blood to the liver, where it is reconverted to glucose

35. a.11 steps ; Location: cytosol b.Original material: glucose (C 6 H 12 O 6 ) c.End product: lactate - Twice substrate level phosphorylations - Net of 2 ATP d. Key enzymes: Hexokinase (HK) ……. energy investment phase Phosphofructokinase 1 (PFK-1) ……. energy investment phase Pyruvate kinase (PK) …….energy payoff phase e. Once dehydrogenation: oxidation Once hydrogenation: reduction f.No oxygen is required Summary of Glycolysis

36. The regulation of glycolysis Hormone regulation Covalent regulation Allosteric regulation Glucagon ATP cAMP ATP ADP F-6-P F-2,6-BP PFK-2 active FBP-2 inactive P P FBP-2 active inactive PFK-2 PiPi PKA ATP ADP PiPi Phosphoprotein Phosphatase F-1,6-BP Glucose ATP ADP PFK-1 AMP Citrate AMP Citrate      － － －  Lactate Adenylate cyclase  Glucose 6-phosphate glycolysis

37. 3. The significance of glycolysis Glycolysis is the emergency energy-yielding pathway, such as play ball, climb mountain.….. Glycolysis is the major way to produce ATP in some tissues, even though the oxygen supply is sufficient, such as RBC, retina, testis, skin……

38. Section 3 Aerobic oxidation of glucose The process of oxidation completely from glucose to CO 2 and H 2 O is named aerobic oxidation This process is the major process to provide energy for most tissues

39. 3 phases of Glucose Aerobic oxidation 2. Oxidation from pyruvate to acetyl CoA in mitochondria (3C to 2C) 3. Tricarboxylic acid cycle and oxidative phosphorylation (2C to 1C) O2O2 O2O2 O2O2 Glucose G-6-P Pyruvate Acetyl CoA TCA cycle H + +e CO 2 H2OH2O cytosolmitochondria 1. Oxidation from glucose to pyruvate in cytosol (6C to 3C)

40. CoASH CH 3 C O C O- O CH 3 C O S CoA NAD+ Pyruvate DH complex 2. Oxidation from pyruvate to acetyl CoA (3C to 2C) Pyruvate+NAD + +HSCoA Acetyl CoA+NADH+H + +CO 2 NADH Acetyl-CoA: a common two-carbon unit

41. E1. pyruvate dehydrogenase （丙酮酸脱氢酶） E2. dihydrolipoyl transacetylase （二氢硫辛酰胺转乙酰酶） E3. dihydrolipoyl dehydrogenase （二氢硫辛酰胺脱氢酶） Pyruvate dehydrogenase complex

42. TPP E1 FAD E3 E2

43. 3. Two stages of the 3rd phase of Glucose Aerobic oxidation Stage I The acetyl-CoA is completely oxidized into CO 2, with electrons collected by NAD and FAD via a cyclic pathway (tricarboxylic acid cycle) Stage II Electrons of NADH and FADH 2 are transferred to O 2 via a series carriers, producing H 2 O and a H + gradient, which will promote ATP formation （ oxidative phosphorylation ） (NEXT CHAPTER)

44. Tricarboxylic acid cycle (2C to 1C) Citric Acid Cycle or Krebs cycle Occurs in mitochondrial matrix Is the biochemical hub of the cell, oxidizing carbon fuels, usually in the form of acetyl CoA, interconversion of carbohydrates, lipids, and some amino acids, as well as serving as a source of precursors for biosynthesis For the citric acid cycle, the goal is to use the oxidative power of O 2 to derive as much energy as possible from the products of glycolysis

45. NADH+H + CO 2 C2C2 NADH+H + CO 2 GTP FADH 2 NADH+H + C6C6 C4C4 C4C4 C5C5 Tricarboxylic acid cycle Substrates required: Oxaloacetic Acid GDP 3NAD + FAD two-carbon units (Acetyl-CoA) Intermediate Reactants: Citric Acid Output: Oxaloacetic Acid GTP 3 NADH FADH 2 2CO 2 (4 high-energy electrons) Each Acetyl-CoA yields 2 CO 2, 3 NADH + H +, 1 FADH 2, 1 GTP

46. C O C CH 2 C O O- -OO CH 3 C O S CoA Citrate synthase CoASH Stage I Tricarboxylic acid cycle Oxaloacetic Acid ＋ ＋ C CH 2 C3C3 HOC2C2 CH 2 C1C1 O O-O O- -OO Citrate 4C 2C 6 C

47. Aconitase cis-aconitate intermediate C H 2 C C C C C O O- O O- -O O H C CH 2 C3C3 HOC2C2 CH 2 C1C1 O O- O O- -OO 6 C

48. Isocitrate DH O- NAD NADH a-ketoglutarate Isocitrate CH 2 CH 2 C C C O O- -O O O CO 2 C CH 2 C HC C C O O O- -O O HOHO 6 C 5 C

49. a-ketoglutarate DH NAD +, CoASH NADHNADH Succinyl CoA a-ketoglutarate CH 2 CH 2 C C C O O- -O O O CH 2 CH 2 C C S O O- CoA O CO 2 5 C4 C

50. GDP, P i GTP Succinyl CoA SuccinylCoA synthetase CH 2 CH 2 C C S O O- CoA O CH 2 CH 2 C C O- O O- O CoASH 4C

51. (FAD) fumarate (FADH 2 ) CH 2 CH 2 C C O- O O- O C C C C O- O O- O H H 4C

52. H2OH2OH2OH2O fumarate malate C C C C O- O O- O H H CHO C CH 2 C OO- -OO H 4C

53. malate DH NAD + NADHNADH malate Oxaloacetic Acid CHO C CH 2 C OO- -OO H C O C CH 2 C O O- -OO 4C

54. Tricarboxylic acid cycle CHCOOH CH 2 COOH HO CH 2 COOH HCCOOH CHCOOHHO NAD + NADH+H + CO 2 CH 2 COOH CH 2 CCOOHO CH 3 C O ~ SCoA O CCOOH CH 2 COOH CH 2 COOH CCOOH CH 2 HO COOH CH 2 COOH CCOOH CHCOOH CoASH GTP CoASH GDP+Pi CH 2 COOH CH 2 COOH FADH 2 FAD H C C O OH C H HO O C CH 2 COOH CH 2 C O SCoA ~ CoASH CO 2 NAD + NADH+H + NAD + NADH+H + citrate synthase isocitrate dehydrogenase  - ketoglutarate dehydrogenase

55. Aerobic oxidation of glucose C 6 H 12 O 6 + 6O 2 + 38 ADP +38 P 6CO 2 + 6H 2 O + 38 ATP

56. Generation of ATP in aerobic oxidation of glucose Total per mole of glucose under aerobic conditions: 38 or 36 (32 or 30) ATPs Reactions Catalyzed by Methods of ATP production formed moles of ATP Glyceraldehyde 3-phosphate dehydrogenase Glycolytic pathway Respiratory chain Oxidation of 2 NADH 6 or 4 /5 or 3 Phosphoglycerate kinase Phosphorylation at substrate level 2 Pyruvate kinase Phosphorylation at substrate level 2 consumption of ATP by reactions catalyzed by hexokinase and phosphofructokinase- 2 Production of acetyl CoA Pyruvate dehydrogenase complex Respiratory chain Oxidation of 2 NADH TCA cycle Isocitrate dehydrogenase Alpha-ketoglutarate Dehydrogenase complex Succinyl CoA synthetase Succinate dehydrogenase Malate dehydrogenase Respiratory chain Oxidation of 2 NADH Phosphorylation at substrate level Respiratory chain Oxidation of 2 FADH2 Respiratory chain Oxidation of 2 NADH 6 or 5 4 or 3 6 or 5 2

57. 3 control points of citric acid cycle : citrate synthase isocitrate dehydrogenase  -ketoglutarate dehydrogenase C2C2 C6C6 C4C4 C4C4 C5C5 Krebs Cycle pyruvate Iso C 6 Regulation of pyruvate dehydrogenase Regulation of aerobic oxidation

58. Regulation of pyruvate dehydrogenase Inhibited by products, NADH & Acetyl CoA Also regulated by covalent modification, the kinase & phosphatase also regulated

59. GTP Acetyl CoA Oxaloacetate CoA Citrate [1] cis - Aconitate Isocitrate  -Ketoglutarate NAD + NADH, CO 2 [2] Succinate GDP [4] Fumarate FAD FADH 2 [5] Malate NAD + NADH [6] CoA, NAD + [3] Succinyl CoA NADH, CO 2 Allosteric inhibitor ADP allosteric activator NADH: allosteric inhibitor GTP allosteric inhibitor The Alosteric regulation of citric acid cycle citrate synthase isocitrate dehydrogenase  - ketoglutarate dehydrogenase

60. * Pastuer effect The total amount of glucose consumed by yeast are about 7 times greater under anaerobic conditions than under aerobic conditions This effect is also seen in muscle under anaerobic conditions The yield of ATP under anaerobic conditions is 2 per molecule; but under aerobic conditions the yield is 38 ATP per glucose Therefore, glucose flux through the pathway is regulated to achieve constant ATP levels or decided by the fate of NADH+H +

61. Section 4 The Pentose Phosphate Pathway (PPP)

62. Pentose phosphate pathway The PENTOSE PHOSPHATE pathway,by carring out oxidation and decarboxylation of the 6-C sugar glucose-6-P, is basically used for the synthesis of NADPH and 5-C sugar ribulose-5-P It plays only a minor role (compared to GLYCOLYSIS) in degradation for ATP energy Other names: Pentose phosphate Shunt Hexose Monophosphate Shunt

63. Two stages: –Oxidative portion (NADPH producing) –Non-oxidative (carbon recycling/unit transferring) Location: cytosol Original material: glucose 6-phosphate End product: NADPH, pentose phosphate Important in adipose tissue, adrenal cortex, liver (biosynthesis) 、 Important in red blood cells (antioxidant reasons) Pentose phosphate pathway

64. G-6-P dehydrogenase CHO C-OH HO-C C-OH CH 2 OP COO - C-OH HO-C C-OH CH 2 OP C C-OH HO-C C C-OH CH 2 OP O O NADP + NADPH + H + + H 2 O STAGE I (Oxidation=NADPH producing and formation of pentose phosphate) Glucose-6-PO 4 6-Phosphoglucono-  - lactone 6-Phospho- gluconate Lactonase G-6-P dehydrogenase: Rate limiting step, controlled by NADP + levels Glucose-6-phosphate Dehydrogenase catalyzes oxidation of the aldehyde (hemiacetal), at C1 of glucose-6-phosphate, to a carboxylic acid, in ester linkage (lactone). NADP + serves as electron acceptor

65. COO - C-OH HO-C-H C-OH CH 2 OP C=O CH 2 OH C-OH CH 2 OP CHO C-OH CH 2 OP C-OH CO 2 NADP + NADPH + H + Ru5P isomerase Ru5P epimerase Ribose-5-PO 4 5-p- 木酮糖 Xylulose-5-PO4 Ribulose-5-PO 4 (Ru5P) 6-Phosphogluconate 6-phosphogluconate Dehydrogenase CH 2 OH C-OH C CH 2 OP C=O HO- STAGE I 6C 5C

66. CH 2 OH C-OH C CH 2 OP C=O HO- CHO C-OH CH 2 OP C-OH CH 2 OP C-OH HO-C C=O CH 2 OH + C-OH CH 2 OP CHO 酮醇转移酶 Transketolase 7-p- 景天糖 Sedoheptulose-7-PO 4 Ribose-5-PO 4 Xyulose-5-PO 4 Glyceraldehyde-3-PO 4 STAGE II ( Non-oxidative=carbon recycling ) 5C 7C 3C

67. C-OH CH 2 OP CHO C-OH CH 2 OP C-OH HO-C C=O CH 2 OH C-OH CH 2 OP CHO C-OH CH 2 OP HO-C C=O CH 2 OH + Glyceraldehyde-3-PO 4 Fructose-6-PO 4 4-p- 赤藓糖 Erythrose-4-PO4 Transaldolase 醛糖移转酶 Sedoheptulose-7-PO 4 STAGE II ( Non-oxidative=carbon recycling ) 3C 7C 4C 6C

68. C-OH CH 2 OP CHO CH 2 OH C-OH C CH 2 OP C=O HO- + C-OH CH 2 OP CHO C-OH CH 2 OP HO-C C=O CH 2 OH + Transketolase Erythrose-4-PO 4 Xylulose-5-PO 4 Glyceraldehyde-3-PO 4 Fructose-6-PO 4 STAGE II ( Non-oxidative=carbon recycling ) glycolysis 4C 5C 3C 6C

69. Sedoheptulose 7-P (7 C) Erythrose 4-P (4C) Ribose 5-P (5 C) Glyceraldehyde 3-P (3C) Fructose 6-P (6C) Fructose 6-P Glyceraldehyde 3-P Glucose ATPADP Glucose 6-P 6-Phosphogluconate Oxidative stage Xylulose 5-P ( 5C) Ribulose 5-P (5C) CO 2 NADPH NADP NADPH Non-oxidative stage Pentose phosphate pathway

70. C5 + C5  C3 + C7 (Transketolase) C3 + C7  C6 + C4 (Transaldolase) C5 + C4  C6 + C3 (Transketolase) 3 C5  2 C6 + C3 (Overall) + + + + + SUMMARY 3CO 2 3 G 6-P C5 + C5 + C5 C3 + C6+ C6 3 Glucose-6-PO 4 + 6 NADP + + 3H 2 O 6 NADPH + 6H+ + 3CO 2 + 2 Fructose-6-PO 4 + Glyceraldehyde-3-PO 4 Per glucose oxidized, 2 NADPHs are formed C7 、 C4 are strictly intermediates Glyceraldehyde-3-PO4 is both an intermediate and finalproduct Fructose-6-PO4 is never used as an intermediate, return to the glycolytic pathway

71. *** The significance of PPP 1.Produce ribose 5-phosphate needed for DNA and RNA synthesis 2. Generate reducing equivalents NADPH 1) Reducing power for biosynthesis of fatty acids, cholesterol, folate, and so on 2) Coenzyme of glutathione reductase to keep the normal level of reduced glutathione 3) NADPH serves as the coenzyme of mixed function oxidases (mono-oxygenases)

72. Section 5 Glycogen Biosynthesis and Degradation

73. Introduction A constant source of blood glucose is an absolute requirement for life - glucose is the preferred energy source for the brain and for cells with few or no mitochondria, such as mature erythrocytes - glucose is an essential energy source in exercising muscle

74. 1. Glycogen is a highly branched homopolymer of a-glucose (polysaccharide) 2. Approx. every 10 residues there is a branch, linked by an a-1,6-glycosidic linkage What is Glycogen? Reducing end a-1,4-glycosidic linkage a-1,6-glycosidic linkage ））

75. Glycogen Biosynthesis(Glycogenesis) Glycogenesis: the process of storing excess glucose as glycogen (In times of plenty the body needs to store fuel) occurs in the cell cytoplasm of liver, muscle & kidney, when blood glucose levels are high Excess glucose is stored (limited capacity) –liver and muscle are major glycogen storage sites liver glycogen used to regulate blood glucose levels –brain cells cannot live for > 5 minutes without glucose muscle glycogen used to fuel an active muscle Glycogenesis involves addition of a-D-glucose residues to the C4 (non- reducing end) of an pre-existing chain

76. Requirement of formation glycogen Glycogenin glycogen synthase glycogen-branching enzyme UDP-glucose pyrophosphorylase

77. Requirement of Formation glycogen Primer –glycogenin acts as the primer to which the first glucose residue is attached –glycogenin also catalyzes attachment of additional glucose units to form chains of up to eight units Glycogen-branching enzyme –takes over at this point –chain cannot extend indefinitely

78. Requirement of Formation glycogen Glycogen Synthase –exists in an active (dephosphorylated) and inactive (phosphorylated) form –relative amount of each form is regulated by cellular level of cAMP –cAMP is regulated by insulin:glucagon ratio High insulin keeps GS in dephosphorylated, active form High insulin can also stimulate dephosphorylation of GS High glucagon activates cAMP which activates PK which phosphorylates and inactivates GS –Glycogen Synthase reaction is primary target of insulin’s stimulatory effect on glycogenesis

79. glycogen primer UTP PPi Glycogenesis

80. glycogen synthase oligo  1,6-glucantransferase Debranching glycogen synthase oligo  1,6-glucantransferase Debranching Glycogenesis

81. Glycogenolysis Glycogenolysis : glycogen  glucose In times of need the body needs to mobilize its’ fuel stores Hepatic glycogen not sufficient during 12 hr fast Glycogen degradation Occurs in cytosol Signal that glucose is needed is given by hormones –epinephrine stimulates glycogen breakdown in muscle –glucagon which stimulates glycogen breakdown in liver in response to low BG –used to sustain blood glucose level between meals and to provide energy during an emergency/exercise

82. Glycogenolysis 1,4 glucose 1-phosphate 12 glucose 1-phosphate 1 glucose phosphorylase a glucan transferase glucosidase phosphorylase a Debranching has two enzyme activities in one peptide: oligo - 1,4 1,4-glucantransferase and 1,6-glucosidase   

83. Glycogen Phosphorylase Regulation Glycogen phosphorylase –exists in a “b” inactive form (dephosphorylated) and an “a” active form (phosphorylated) –phosphorylase kinase converts glycogen phosphorylase to active form “a” via addition of inorganic phosphate phosphorylase kinase also exists in an active “a” and an inactive “b” form –activated by cAMP-dependent protein kinase; it is also activated by calcium ions –PK is activated by glucagon and epinephrine »via 2nd messenger cAMP

84. Glycogen Phosphorylase Regulation Glycogen phosphorylase “a” (active) is converted to “b” form by phosphoprotein phosphatase –Stimulated by insulin Glycogen phosphorylase can also be regulated by allosterically –GP “b” inactive form can be converted to GP “b” active form by high AMP –GP “b” active form can be converted back to GP “b” inactive form by high ATP

85. Regulation of Glycogenesis and Glycogenolysis

86. The significance of glycogenesis and glycogenolysis - Liver glycogen (as much as 10% of liver wet weight) functions as a glucose reserve for maintaining blood glucose concentration - Muscle glycogen (total 400 gram) serves as a fuel reserve for synthesis of ATP within that tissue

87. Section 6 Gluconeogenesis

88. *** Gluconeogenesis Synthesis of glucose from non-CHO precursors –Lactate, most amino acids and glycerol *** –Lactate and amino acids (except leucine and lysine) are converted to either pyruvate or OAA (oxalloacetate) –Glycerol is converted (phosphorylated) to G3P and then to dihydroxyacetone phosphate Occurs primarily in liver, sometimes kidney

89. Blood Glucose Ribose 5-PO 4 Glycogen L-lactate Pyruvate PEP 2PGA 3PGA 1,3bisPGA Gly-3-P F1,6bisP OAA F6P G6P DHAP Glucose H2OH2O PO 4 Phosphatase H2OH2OPO 4 Phosphatase Kinase Gluconeogenesis

90. Reversal of glycolysis except at 3 steps –HK(GK), PFK and PK 3 Steps need to be bypassed Hexokinase and Phosphofructokinase are bypassed by glucose 6 phosphatase and fructose 1,6-bisphosphatase Pyruvate Kinase bypass involves formation of OAA as an intermediate –OAA in mitochondrial matrix cannot directly cross membrane so is converted to malate

91. Gluconeogenesis Bypass of PK reaction continued –Malate and aspartate can transverse mitochondrial matrix converted back to OAA in cytoplasm –OAA is decarboxylated and phosphorylated to PEP by PEP carboxykinase Carbon skeletons of many amino acids that enter TCA cycle can thus be used for glucose synthesis (glucogenic amino acids)

92. Bypasses in Gluconeogenesis-1 (2 reactions) Pyruvate Carboxylase (Gluconeogenesis) catalyzes: pyruvate + HCO 3 - + ATP  oxaloacetate + ADP + P i PEP Carboxykinase (Gluconeogenesis) catalyzes: oxaloacetate + GTP  PEP + GDP + CO 2 C C C H 2 O O - OPO 3 2 - C C C H 3 O O - O ATP ADP + P i C CH 2 C C O O O - O - O HCO 3 - GTP GDP C O 2 pyruvate oxaloacetate PEP Pyruvate Carboxylase PEP Carboxykinase

93. Fructose 1,6 bi-sphosphatase glycolysis ATPADP Fructose 1,6-2 PO 4 Fructose-6-PO 4 H2OH2OPO 4 Gluconeogenesis Mg 2+ Bypasses in Gluconeogenesis-2

94. Glucose-6-Phosphatase (Gluconeogenesis) catalyzes: glucose-6-phosphate + H 2 O  glucose + P i H O OH H OHH OH CH 2 OH H OH H H O OH H OHH OH CH 2 OPO 3 2 - H OH H H 2 O 1 6 5 4 3 2 + P i glucose-6phosphate glucose Glucose 6 phosphatase Bypasses in Gluconeogenesis-3

95. Substrate cycle or futile cycle: nothing is accomplished but the waste of ATP. In substrate cycle, ATP is formed in one direction and then is hydrolyzed in the opposite direction. Substrate cycle produces net hydrolysis of ATP We must remember that the direction of the substrate cycle is strictly controlled by allosteric effectors to meet the needs of the body for energy Substrate cycle is a pair of opposed irreversible reactions

96. Glucose Paradox Evidence that glucose ingested during a meal is not used to form glycogen directly Glucose is first taken up by RBCs in bloodstream and converted to lactate by glycolysis Lactate is taken up by liver and converted to G6P by gluconeogenesis G6P converted to glycogen

97. 1.To keep blood sugar level stable 2.To replenish liver glycogen 3. To clear the products of other tissues’ metabolites from the blood 4. To convert glucogenic amino acids to glucose 5. To regulate acid-base balance The significance of gluconeogenesis

98. Cori Cycle （ Muscles lack G6-phosphatase ） - used to prevent high blood lactate levels and to fuel muscle activity - l-actate leaves muscle cells - transported via blood to liver - liver converts to glucose - glucose released back into circulation - returned to muscles

99. F-6-P F-1,6-BP phosphofructokinase-1 F-1,6-biphosphatase ATP citrate ADP AMP F-2,6-BP F-1,6-BP insulin glucokinase phosphofructokinase-1 pyruvate kinase glycolysis gluconeogenesis pyruvate carboxylase phosphoenolpyruvate carboxykinase fructose 1,6-biphosphatase glucose 6-phosphatase glucagon Glucocorticoids epinephrine Regulation of gluconeogenesis and glycolysis

100. ***** Section VII Blood Sugar and Its Regulation Blood sugar 3.89~6.11mmol/L Origin (income) Fate (outcome) Dietary supply Liver glycogen Gluconeoesis (non-carbohydrate) Other saccharides 8.89--10.00mmol/L (threshold of kidney) glycogen glycogenesis urine glucose aerobic oxidation CO 2 + H 2 O + energy PPP other saccharides non-carbohydrates (lipids and some amino acids)

101. glycogenolysis 1 2 2 3 4 5 5 6 Regulation of high Blood Sugar insulin High blood sugar leve l (hyperglycemia) insulin receptor active transport in muscle and adipose tissue cells (not in liver and brain) glycolysis and aerobic oxidation glycogenesis proteinsynthesis lipogenesis lipolysis gluconeogenesis modulating system cAMP

102. cAMP Modulating system 11 3 3 4 2 Regulation of Low Blood Sugar

103. 选择题练习 糖代谢

104. 1. 糖类最主要的生理功能是 ( ) A 提供能量 B 细胞膜组分 C 软骨的基质 D 信息传递 E 免疫作用

105. 2. 关于糖类消化吸收的叙述, 错误的是 ( ) A 食物中的糖主要是淀粉 B 消化的部位主要是小肠 C 部分消化的部位可在口腔 D 胰淀粉酶将淀粉全部水解成葡萄糖 E 异麦芽糖酶可水解  -1,6- 糖苷键

106. 3. 关于糖酵解途径中的关键酶正确的是 ( ) A 磷酸果糖激酶 -1 B 果糖双磷酸酶 -1 C 磷酸甘油酸激酶 D 丙酮酸羧化酶 E 果糖双磷酸酶 -2

107. 4. 1 分子葡萄糖在有氧或无氧条件下经酵解途 径氧化产生 ATP 分子数之比为 ( ) A 2 B 4 C 6 D 19 E 36

108. 5. 1 分子乙酰 CoA 经三羧酸循环氧化后的产物是 ( ) A 柠檬酸 B 草酰乙酸 C 2CO 2 + 4 分子还原当量 D CO 2 +H 2 O E 草酰乙酸 +CO 2

109. 6. 三羧酸循环主要在细胞的哪个部位进行 ? A 胞液 B 细胞核 C 微粒体 D 线粒体 E 高尔基体

110. 7. 磷酸戊糖途径是在哪个亚细胞部位进行的 ? A 胞液中 B 线粒体 C 微粒体 D 高尔基体 E 溶酶体

111. 8. 磷酸戊糖途径主要的生理功用 ( ) A 为核酸的生物合成提供核糖 B 为机体提供大量 NADPH+H + C 生成 6- 磷酸葡萄糖 D 生成 3- 磷酸甘油醛 E 生成 6- 磷酸葡萄糖酸

112. 9. 关于糖原合成的叙述错误的是 ( ) A 葡萄糖的直接供体是 UDPG B 从 1- 磷酸葡萄糖合成糖原不消耗高能磷酸键 C 新加上的葡萄糖基连于糖原引物非还原端 D 新加上的葡萄糖基以  -1,4 糖苷键连于糖原引物上 E 新加上的葡萄糖基连于糖原引物 C 4 上

113. 10. 下例哪种酶不是糖异生的关键酶 ? A 丙酮酸羧化酶 B 磷酸烯醇式丙酮酸羧基酶 C 磷酸甘油酸激酶 D 果糖双磷酸酶 E 葡萄糖 6- 磷酸酶

114. 11. Which one is the main organ that regulate blood sugar metabolism? A brain B kidney C liver D pancreas E adrenal gland

115. 12. The end product of glycolytic pathway in human body is ( ) A CO 2 and H 2 O B pyruvic acid C acetone D lactic acid E oxalacetic acid

116. 13. Which one can promote synthesis of glucogen, fat and protein simultaneously? A glycagon B insulin C adrenaline D adrenal cortex hormone E glucocorticoid

117. 14. Which one is the allosteric inhibitor of 6-phosphofructokinase-1? A 1,6-diphosphofructose B 2,6 -diphosphofructose C AMP D ADP E citric acid

118. 15. 关于糖酵解的叙述, 下列那些是正确的 ? A 整个过程在胞液中进行 B 糖原的 1 个葡萄糖单位经酵解净生成 2 分子 ATP C 己糖激酶是关键酶之一 D 是一个可逆过程 E 使 1 分子葡萄糖生成 2 分子乳酸

119. 16. 三羧酸循环中, 不可逆的反应有 ( ) A 柠檬酸 → 异柠檬酸 B 异柠檬酸 →  - 酮戊二酸 C  - 酮戊二酸 → 琥珀酰 CoA D 琥珀酸 → 延胡索酸 E 苹果酸 → 草酰乙酸

120. 17. 如果摄入葡萄糖过多, 在体内的去向是 ( ) A 补充血糖 B 合成糖原储存 C 转变为脂肪 D 转变为唾液酸 E 转变为非必需脂肪酸

121. 18. 胰岛素降血糖的作用是 ( ) A 促进肌肉脂肪等组织摄取葡萄糖 B 激活糖原合成酶促糖原的合成 C 加速糖的氧化分解 D 促进脂肪动员 E 抑制丙酮酸脱氢酶活性

122. 19. The cofactors of pyruvic dehydrogenase complex is ( ) A thioctic acid B TPP C CoA D FAD E NAD +

123. 20. The high-energy compounds produced by substrate level phosphorylation in glyco-aerobic oxidation are ( ) A ATP B GTP C UTP D CTP E TTP