洪錦堂 老師 醫學大樓 0866 室 講義在我個人網站 ( 生化科 )

1. 洪錦堂 老師醫學大樓0866室講義在我個人網站(生化科) • Chapter 14Glycolysis, gluconeogenesis, and the pentose phosphate pathway • Chapter 15Principles of metabolic regulation: Glucose and glycogen • Chapter 16The citric acid cycle • Chapter 19Oxidative phosphorylation

2. To remind you….. • Class schedule • Exam

3. GlycolysisGluconeogenesisPentose phosphate pathway Chapter 14

4. Metabolism: Catabolism & Anabolism • Catabolic pathways converge to a few end products • Anabolic pathways diverge to synthesize many biomolecules • Some pathways serve both in catabolism and anabolism, such pathways are amphibolic

5. Outline • 14.1 Glycolysis • First Phase of Glycolysis (preparatory phase) • Second Phase of Glycolysis (lysis phase) • 14.2 Feeder pathways for glycolysis • 14.3 Fates of pyruvate under anaerobic conditions: Fermentation • 14.4 Glucogenesis • 14.5 Pentose phosphate pathway of glucose oxidation

6. 14.1 Glycolysis Why glucose? 1. Complete oxidation yields 2,840 KJ/mol 2. low cytosolic osmolarity 3. capable of supplying a huge array of metabolic intermediates for biosynthetic reactions

7. Glycolysis 又稱 The Embden-Meyerhof (Warburg) Pathway 1. Consume 2 ATP in 1st phase, produce 4 ATP in 2nd phase: net gain 4 - 2 = 2 ATP 2. Glucose(6C)  2＊3C (pyrurate) 3. Pyruvate is used in 3 ways:

8. Alcohol fermentation Lactate fermentation O2

9. Hexokinase Phosphohexose isomerase Phospho- Fructosekinase-1 Aldolase Triose phosphate isomerase

10. Glyceraldehyde 3-phosphate Dehydrogenase Phospho- Glycerate Kinase Phospho- Glycerate Mutase Enolase Pyruvate kinase

11. Glycolytic enzyme命名 (1) Kinase與ATP水解or 合成相關之enzyme (2) Mutase( 轉換)Transfer functional group from one position to another in the same molecule, 指～P由C3位置C2位置 (3) Isomerase指Aldose Ketose (4) Aldolase指產物各為-Aldose分子及ketose分子 (5) Enolase產生enol form 分子 -C=C- alcohol ※Mutase is a subclass of isomerase

12. First Phase of Glycolysis • The first reaction - phosphorylation of glucose • Hexokinase or glucokinase • This is a priming reaction - ATP is consumed here in order to get more later • ATP makes the phosphorylation of glucose spontaneous

13. Reaction 1: Phosphorylation of glucose spontaneous and irreversible

14. Glucokinase: Km 10 mM only turns on when cell is rich in glucose Not inhibited by G6P Exist in liver Specific for glucose Hexokinase is allosterically inhibited by its reaction product • Hexokinase: • Km 0.1 mM • So hexokinase is normally active! • Inhibited by G6P reversibly • Glucose, mannose….

15. Reaction 2: Phosphohexose isomerase (phosphoglucose isomerase) Reaction 3: Phosphofructose kinase (PFK-1)---- 2nd priming step Irreversible

16. Reaction 4: Fructose 1,6-bisphosphate Aldolase In erythrocyte –0.23kJ/mol

17. Reaction 5: DHAP→Glyceraldehyde 3-P by triose-phosphate isomerase

18. Glycolysis - Second Phase • Metabolic energy produces 4 ATP • Net ATP yield for glycolysis is two ATP • Second phase involves two very high energy phosphate intermediates • . • 1,3 BPG • Phosphoenolpyruvate

19. Reaction 6: Glyceraldehyde-3-phosphate dehydrogenase 1.Addition of a phosphate group to G3P 2.e- transfer from G3P to NAD+ (hydride H:-) 3.No ATP or ADP is involved

20. Reaction 7: Phosphoryl transfer from 1,3 bisphosphoglycerate to ADP Pay off

21. Substrate-level phosphorylation The formation of ATP by phosphoryl transfer from a substrate such as 1,3 BPG is referred as a substrate-level phosphorylation. It involves soluble proteins and chemical intermediates. Respiration-linked (oxidative) phosphorylation (氧化磷酸化) involves membrane-bound enzymes and transmembrane gradients of protons.

22. Reaction 8:Conversion of 3-phosphoglycerate to 2 phosphoglycerate Reaction 9: Dehydration of 3- to 2- phosphoenolpyruvate by enolase(烯醇酉每) 高能量

23. Reaction 10: Transfer of the phosphoryl group from phosphoenolpyruvate to ADP This is referred to as "substrate-level phosphorylation Payoff

24. SUMMARY 14.1 Glycolysis • Glycolysis is a near-universal pathway by which a glucose molecule is oxidized to two molecules of pyruvate, with energy conserved as ATP and NADH. 2. All ten glycolytic enzymes are in the cytosol, and all ten intermediates are phosphorylated compounds of three or six carbons.

25. SUMMARY 14.1 Glycolysis 3. In the preparatory phase of glycolysis, ATP is invested to convert glucose to fructose 1,6-bisphosphate. The bond between C-3 and C-4 is then broken to yield two molecules of triose phosphate.

26. 4e- SUMMARY 14.1 Glycolysis 4. In the payoff phase, each of the two molecules of glyceraldehyde 3-phosphate derived from glucose undergoes oxidation at C-1; the energy of this oxidation reaction is conserved in the formation of one NADH and two ATP per triose phosphate oxidized. The net equation for the overall process is Glucose+2NAD++2ADP+2Pi 2pyruvate+2NADH+2H+ +2ATP+2H2O

27. SUMMARY 14.1 Glycolysis 5. Glycolysis is tightly regulated in coordination with other energy-yielding pathways to assure a steady supply of ATP. Hexokinase, PFK-1, and pyruvate kinase are all subject to allosteric regulation that controls the flow of carbon through the pathway and maintains constant levels of metabolic intermediates.

28. 14.2 Feeder pathways for glycolysis Glycogen and starch Maltose, lactose, trehalose, sucrose Fructose, mannose, galactose

30. Fig. 14-11Conversion of galactose to glucose 1-phosphate

31. Galactosemia

32. Catabolism of glycogen • Cellular glycogen • Dietary glycogen

33. Catabolism of cellular glycogen Glycogen phosphorylase catalyzes an attack by Pi on the (a1→4) glycosidic linkage that joins the last two glucose residues at a nonreducing end, generating glucose 1-phosphate and a polymer one glucose unit shorter. 14-10

35. Glucose 1-phosphate produced by glycogen phosphorylase is converted to glucose 6-phosphate by phosphoglucomutase, which catalyzes the reversible reaction Glycolysis Pentose phosphate pathway

36. Dietary polysaccharides and disaccharides are hydrolyzed to monosaccharides by various enzymes a-amylase: Salivary---digest to short polysaccharide fragment or oligosaccharides Pancrease---digest to disaccharides (maltose), trisaccharides (maltotrioses) and dextrins

37. Intestine secrects enzymes to digest dextrin and disaccharides

38. Catabolism of dietary and cellular glycogen

39. Lactose intolerance:乳糖不耐症 Lack lactase Diarrhea and discomfort Undigested lactose and its metabolites increase the osmolarity of the intestinal contents, favoring the retention of water in the intestine.

40. Anaerobic Metabolism and tooth decay (蛀牙) Sucrose Plaque (polysaccharide) Products of anaerobic glycolysis carried out by bacteria lactate and pyruvate tooth decay

41. SUMMARY 14.2 Feeder Pathways for Glycolysis 1. Glycogen and starch, polymeric storage forms of glucose, enter glycolysis in a two-step process. Phosphorolytic cleavage of a glucose residue from an end of the polymer, forming glucose-1 phosphate, is catalyzed by glycogen phosphorylase or starch phosphorylase. Phosphoglucomutase then converts the glucose 1-phosphate to glucose 6-phosphate, which can enter glycolysis.

42. SUMMARY 14.2 Feeder Pathways for Glycolysis 2. Ingested polysaccharides and disaccharides are converted to monosaccharides by intestinal hydrolytic enzymes, and the monosaccharides then enter intestinal cells and are transported to the liver or other tissues.

43. SUMMARY 14.2Feeder Pathways for Glycolysis 3. A variety of D-hexoses, including fructose, galactose, and mannose, can be funneled into glycolysis. Each is phosphorylated and converted to either glucose 6-phosphate or fructose 6-phosphate.

44. SUMMARY 14.2 Feeder Pathways for Glycolysis 4. Conversion of galactose 1-phosphate to glucose 1-phosphate involves two nucleotide derivatives: UDP-galactose and UDP-glucose. Genetic defects in any of the three enzymes that catalyze conversion of galactose to glucose 1-phosphate result in galactosemias of varying severity.

45. 14.3 Fates of Pyruvate under Anaerobic Conditions: Fermentation O2

46. Anaerobic pathways 乙醛 yeast muscle Fetal Alcohol syndrome

47. Thiamine Pyrophosphate Carries “Active Acetaldehyde” Groups • Thiamine pyrophosphate (TPP), a coenzyme derived from vitamin B1. • Lack of vitamin B1 in the human diet leads to the condition known as beriberi. • Thiamine pyrophosphate plays an important role in the cleavage of bonds adjacent to a carbonyl group, such as the decarboxylation of -keto acids, and in chemical rearrangements in which an activated acetaldehyde group is transferred from one carbon atom to another

48. Thiamine Pyrophosphate Carries “Active Acetaldehyde” Groups

49. Replenishment of NAD+ 1. under anaerobic condition : Lactic acid fermentation 2. under anaerobic condition : Alcoholic fermentation 3. under aerobic condition : Mitochondria oxidation of each NADH to yield 2.5 (1.5) ATP

50. Oxygen debt Cori cycle