Part Two METABOLISM
Metabolism of Carbohydrate Biological Oxidation Metabolism of Lipids Metabolism of Proteins Metabolism of Nucleotides Regulation of Metabolism Substance synthesis and decompose
Chapter Four Metabolism of Carbohydrates
Carbohydrate chemistry 1. Concept of Carbohydrate Carbohydrates are aldehyde or ketone derivatives of polyhydric alcohols hydroxy group
2. Category and naming They are classified as follows Monosaccharide Disaccharides Oligosaccharide Polysaccharide Glycoconjugate
(1) Monosaccharide glucose——hexoaldoses fructose——hexoketoses 目 录
(2) Disaccharides two molecules of monosaccharide maltose, sucrose, lactose.
Sugars with four, five, six or seven carbons are called tetroses, pentose, hexoses and heptoses respectively.
(3) Polysaccharides Yield a lot of monosaccharides when hydrolyzed starch, cellulose ,glycogen
① starch, mainly stored in plant 淀粉颗粒 α-1,6-glycosidic bond α-1,4-glycosidic bond 目 录
② glycogen, mainly stored in animals α-1,4-glycosidic bond α-1,6-glycosidic bond 目 录
Single cellulose molecule β-1,4-glycosidic bond ③ cellulose, function as framework of plants Hydrogen bond Cellulose fiber Microfiber 目 录
(4) Glycoconjugates They refer to the compounds consisting of saccharide and nonsaccharide, such as protein, lipid etc. Including: Glycolipid, is the compound constituted by saccharide and lipid. Glycoprotein, is the compound constituted by saccharide and protein. Proteoglycans, is the structural elements in connective tissues.
Section One Introduction
1. To be oxidized and to supply energy This is the major function of saccharide The physiological functions of saccharides 2. Work as remarkably versatile precursors for biosynthetic reactions such as amino acid, fat, cholesterol, nucleoside 3. Participate in the composition of tissue cells in organism. Such as glycoprotein, proteoglycan, glycolipid
1. Digestion and Absorption of Carbohydrates 1.1 Digestion of Carbohydrates starchare the major dietary carbohydrate source for human. Other carbohydrate sources include glycogen, maltose, sucrose, lactose and glucose. Digesting place: Mainly in small intestine, less in mouth.
Process of digesting Starch Mouth Stomach α-amylase in saliva Small intestine α-amylase in pancreatic juice maltose+maltotriose （40%） （25%） α-limit dextrins+isomaltose （30%） （5%） The surface of the small intestinal epithelial cells α-limit dextrinase α-glucosidase Glucose
The cellulose existing abundant in diet are useful for the human health due to that they can stimulate the moving of intestine, even though they can not be digested because of lacking of -glucosidase in human intestine.
1.2 Absorption of Carbohydrates (1) Absorption place the upper small intestine (2) Molecule absorbed Monosaccharide, mainly glucose
Na+pump (3) Mechanism of absorption lumen membrane Intracellular membrane Small intestinal epithelial cell Portal vein Intestine lumen K+ ATP ADP+Pi Na+ G Na+-dependent glucose transporter, SGLT
1.3 Absorption route of Carbohydrates SGLT Small intestinal epithelial cells Small intestine lumen SGLT---- Na+ (Sodium)-glucose transporter Portal vein GLUT, refer to glucose transporter. There are five kinds of GLUT having been found Liver GLUT Various tissue cells Blood circulation
ATP glycogenesis glycogenolysis Aerobic Anaerobic Digestion and absorption Gluconeogenesis Other substances glycogen 2. The Fate of Absorbed Glucose H2O and CO2 Pentose phosphate pathway glycolysis ribose + NADPH+H+ Glucose Pyruvate Lactate Starch Lactate, amino acid, glycerol
Section Two Anaerobic degradation of Glucose Glycolysis
1. Basic Process of Glycolysis * Definition of Glycolysis The process in which a molecule of glucose is degraded in a series of enzymatic reactions to yield two molecules of pyruvate or lactate under anaerobic condition is term glycolysis. * The site of glycolysis is cytoplasm.
The basic process of glycolysis can be divided into two stages: • The first stage The reaction process from glucose to pyruvate is called glycolytic pathway • The secondary stage The reaction process from pyruvate to lactate
Glu ATP ADP G-6-P F-6-P ATP ADP F-1,6-2P 3-PGA DHAP NAD+ NADH+H+ hexokinase 1,3-DPGA ADP ATP 3-PGA Glucose-6-phosphate 2-PGA Glucose PEP One of key enzymes ADP ATP Pyruvate 1.1 Pyruvate Formation from Glucose (1) Glucose is phosphorylated to be glucose-6-phosphate
Now it has been found that there are four kinds of isoenyzme of hexokinase in mammal animals called hexokinase I to IV type, respectively.In liver, it is hexokinase IV, namelyglucokinase. The characters of glucokinase are: ① The affinity to glucose is very low (high Km, Km ~10 mmol/L, p131 error) ② It is regulated by hormones
Glu ATP ADP G-6-P F-6-P ATP ADP F-1,6-2P 3-GAP DHAP Phosphohexose isomerase NAD+ NADH+H+ 1,3-DPGA ADP ATP 3-PGA Fructose-6-phosphate Glucose-6-phosphate 2-PGA PEP ADP ATP Pyruvate ⑵ Glucose-6-phosphate →Fructose-6-phosphate
Glu ATP ADP G-6-P F-6-P ATP ADP F-1,6-2P 3-GAP DHAP Phosphofructokinase-1 NAD+ NADH+H+ 1,3-DPGA Fructose-6-phosphate Fructose-1,6-bisphosphate ADP ATP 3-PGA 2-PGA PEP One of key enzymes ADP ATP Pyruvate (3) fructose-6-phosphate → Fructose-1,6-bisphosphate
Glu ATP ADP G-6-P F-6-P ATP ADP F-1,6-2P aldolase 3-GAP DHAP NAD+ Dihydroxyacetone phosphate, DHAP NADH+H+ 1,3-DPGA Fructose-1,6-bisphosphate ADP Glyceraldehyde-3-phosphate, 3-PGA ATP 3-PGA 2-PGA PEP ADP ATP Pyruvate (4) phosphohexose →2 molecules of phosphotriose
Glu ATP ADP G-6-P F-6-P ATP phosphotriose isomerase ADP F-1,6-2P 3-GAP DHAP NAD+ NADH+H+ 1,3-DPGA ADP ATP Dihydroxyacetone phosphate Glyceraldehyde-3-phosphate 3-PGA 2-PGA PEP ADP ATP Pyruvate (5) Phosphotrioses interconverse
Glu ATP ADP G-6-P F-6-P ATP ADP F-1,6-2P 3-GAP DHAP Glyceraldehyde-3-phosphaste dehydrogenase NAD+ NADH+H+ 1,3-DPGA ADP Glyceraldehyde-3-phosphaste 1,3-bisphosphoglycerate ATP 3-PGA 2-PGA PEP ADP ATP Pyruvate (6) glyceraldehyde-3-phosphate→1,3-bisphosphoglycerate
Glu ATP ADP G-6-P F-6-P ATP ADP F-1,6-2P Phosphoglycerate kinase 3-GAP DHAP ADP ATP NAD+ 1,3-bisphosphoglycerate NADH+H+ 3-phosphoglycerate 1,3-DPGA ADP ATP 3-PGA 2-PGA PEP ADP ATP Pyruvate (7) 1,3-bisphosphoglycerate→3-phosphoglycerate Substrate-level phosphorylation high-energy compound
Substrate-level phosphorylation is the production of ATP from ADP by a direct transfer of a high-energy phosphate group from a high-energy transfer compound. 1,3-bisphosphoglycerate
Glu ATP ADP G-6-P F-6-P ATP ADP F-1,6-2P Phosphoglycerate mutase 3-GAP DHAP NAD+ NADH+H+ 1,3-DPGA 3-phosphoglycerate 2-phosphoglycerate ADP ATP 3-PGA 2-PGA PEP ADP ATP Pyruvate (8) 3-phosphoglycerate→2-phosphoglycerate
Glu ATP ADP G-6-P F-6-P ATP ADP F-1,6-2P 3-GAP DHAP enolase NAD+ NADH+H+ 1,3-DPGA ADP phophoenolpyruvate 2-phosphoglycerate ATP 3-PGA 2-PGA PEP ADP ATP Pyruvate (9) 2-phosphoglycerate →phophoenolpyruvate, PEP
Glu ATP ADP G-6-P F-6-P ATP ADP F-1,6-2P Pyruvate kinase 3-GAP DHAP NAD+ ADP NADH+H+ pyruvate 1,3-DPGA Phosphoenolpyruvate ADP ATP ATP 3-PGA 2-PGA PEP One of key enzymes ADP ATP Pyruvate (10) Phosphoenolpyruvate → pyruvate, and yield ATP through substrate level phosphorylation
NADH + H+ NAD+ Lactate dehydrogenase, LDH 1.2 Conversion of Pyruvate to Lactate lactate pyruvate Here, the NADH+H+in the reaction comes from the six step in the above, the dehydrogenation reaction of 3-phosphoglyceraldehyde
Glu G-6-P F-6-P F-1, 6-2P ADP ATP ATP ADP DHAP 3-GAP E1:hexokinase NAD+ E2: 6-PFK-1 NADH+H+ 1,3-DPG E3: Pyruvate kinase ADP ATP 3-PGA lactate NAD+ 2-PGA NADH+H+ ATP ADP Pyruvate PEP E1 E2 Glycolysis metabolism E3 制作：吴耀生
ATP ATP ADP ADP ADP ATP G-6-P G hexokinase F-6-P F-1,6-2P PFK-1 pyruvate PEP Pyruvate kinase Summary for glycolysis (1) Reaction site：in cytoplasm (2) It is a process toproduce energybut without the need for oxygen (3) There arethree irreversible reactionsteps
(4) The manner to yield energy and the number of ATP produced. Manner：substrate level phosphorylation The net number of yielding ATP ： If to begin from Glucose, 2×2-2= 2ATP If to begin from Glycogen, 2×2-1= 3ATP (5) The fate of the final product lactate To be released into blood stream, and then to be taken into liver metabolized. To be decomposed and utilized further To go into Lactate cycle ( gluconeogenesis）
galactose Galactose kinase Galactose-1-phosphate Glu Mannose ATP ADP hexokinase G-6-P Glucose-1-phosphate mutase Mannose-6-phosphate mutase F-6-P ATP hexokinase ADP fructose F-1,6-2P pyruvate Except for glucose, other hexose can converse to phosphohexose and then go into glycolysis pathway.
①hexokinase ②6-phosphofructokinase-1 ③pyruvate kinase ① allosteric regulation ② covalent modification 2. Regulation of Glycolysis Key enzymes Regulation models
3. The significance of Glycolysis (1) Glycolysis is the emergency energy-yielding pathway. (2) Glycolysis is the main way to produce ATP in some tissues, even though the oxygen supply is sufficient In cells without mitochondria, red blood cells In metabolism active cells, retina, testis, skin, medulla of kidney.
Section Three Aerobic Oxidation of Glucose
Concept The process of complete oxidation of glucose to CO2 and water with release of energy as the form of ATP is termedaerobic oxidation. The place for aerobic oxidation：cytoplasm, and mitochondria