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Metabolism of carbohydrates

1. summarize

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2. Digestion & absorption

• Hydrolyzed by enzyme

• active absorptive process

at small intestine

• Final products - glucose

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3.blood sugar

• the sources & outlet

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Blood glucoseLiver glycogen

Dietary carbohydrate

Glucogenesis (A.A,lactate,etc)

Liver ,muscle glycogen

Catabolism (H20,CO2,ATP)

Other substrates

glycosuria

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• blood sugar concentration is

regulated by tissues,hormones

Decreasing blood sugar level:

hormone insulin

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elevating blood sugar level:

hormone

Glucagon,epinephrine,glucocorticoid, growth hormone

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Blood glucoseLiver glycogen

Dietary carbohydrate

Glucogenesis (A.A,lactate,etc)

Liver ,muscle glycogen

Catabolism (H20,CO2,ATP)

Other substrates

glycosuria

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Hyperglycosemia: >7.2mmol/L

Hypoglycosemia: <3.9mmol/L

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• The tolerance to carbohydrates

Tolerance test for glucose

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4. the catabolic pathway of

carbohydrates

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catabolic pathway of

carbohydrates

anaerobic glycolysis

Aerobic

oxidationpentose pathway

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A. Anaerobic glycolysis

• concept

Glycolysis is the sequence of reactions that converts glucose into lactate with the concomitant production of ATP,under anaerobic conditions

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• the reaction site: cytosol

• basic process

(4 phases)

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1) phosphorylation of hexoses

GG6P

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G6PF6P

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F6P FBP

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• the characteristics of

HK,PFK

• the changes of the energy

• the significance

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己糖激酶（ HK ） a 二亚基的变构酶 b 催化不可逆反应，关键酶 ΔGo = -4.5 Kcal/mol c 葡萄糖激酶是肝中存在的己糖激酶的

同工酶

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名称 己糖激酶 葡萄糖激酶

存在 各组织细胞 肝细胞

底物 G G

产物 G6P G6P

Km 0.01-0.1mM 10-20mM

抑制剂 G6P ——

高糖膳食后，肝中的 G G6P Gn 储存

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磷酸果糖激酶（ PFK ）

a 四亚基的变构酶

b 催化不可逆反应 关键酶

ΔGo = -3.4 Kcal/mol

c 酵解过程中的主要限速酶

★ 、 磷酸化酶 （ phosphorylase ）

a 催化反应， α-1,4 糖苷键

磷酸解

b 产物 G1P Gn-1

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2) Formation of glyceraldehyde-3-

phosphate (G3P) by cleavage and

isomerization

DAP

DAPG3P

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3) Formation of pyruvate

a. dehydrogenation

G3P

BPG

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b. energy released

BPG 3PG

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c. transfer phosphoryl group

3PG 2PG

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d. dehydrate

2PG PEP

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e. energy released

PEP

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4) reduction of pyruvate to

lactate

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• summarize

a. concept

b. the reaction site c. basic process (4 phases)

d.key enzyme,limited enzyme

e. the changes of energy

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Consumption & generation of ATP

in glycolysis

reaction ATP change per glucose

G-----------G6P - 1

F6P--------FBP -1

(2) BPG----(2) 3PG +2

(2)PEP-------(2)pyruvate +2

net +2

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f. characteristics

g. Physiologic role of glycolysis

• the control of glycolysisa. enzymes

b. hormones

c. ATP/ADP

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LDH

CH3 - C- COOH CH3-CH-COOH

O OH

+ + NADH+H+ NAD+

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B. Aerobic oxidation of glucose

• general

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lactate pyruvate acetyl CoA

Citric acid cycle

Biological oxidation

CO2,H2O, energy

O2 lack of O2

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• the reaction site

• basic process

(3 phases)

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1) glycolysis

(G----------pyruvate)

2) formation of acetylCoA

from pyruvate

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• Components of pyruvate dehydrogenase

complex

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3) Citric acid cycle

a. acetyl CoA entering Citric

acid cycle

(synthesis of citric acid )

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b. dehydrogenation & decarboxylation

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• In this stage produced:

2 molecules of CO2

2 pairs of NADH+H+

1 molecule of GTP

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c. Regenesis of oxaloacetate

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• the sources of oxaloacetate

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• In this stage produced:

1 pairs of FADH2

1 pairs of NADH+H+

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• summarize a. concept

b. the reaction site c. basic process (3 phases)

d. key enzyme

e. the changes of energy

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(32)

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NADH+H+ FADH2 ATP GTP CO2 H2O

Formation of pyruvate

2 （ 1 ） 2 或 3

2 （ 1）

2 （ 1 ）

acetyl

CoA enter TCA cycle

2 （ 1 ） 2 （ 1

）

2 （ 1）

2 （ 1）

2 （ 1 ） 2 （ 1 ）

2 （ 1 ）

2 （ 1 ）

2 （ 1 ）

formation of acetyl CoA

2(1)

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Glucose+6O2 6CO2+6H2O = -2790kJ/mol

30.5KJ38/2790KJ=41%

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f. characteristics

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g. Physiologic role of aerobic

oxidation of glucose & TCA

cycle

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• the control of aerobic

oxidation of glucose & TCA

cycle

Pasteur effect

crabtree effect

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a. enzymes

b. hormones

c. ATP/ADP

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C .Pentose phosphate pathway

(hexose monophosphate shunt)

• general

• the reaction site

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• basic process

(2 phases)

a. Oxidation stage

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b. non oxidation stage

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C3

C7

C6

C4

C3

C6

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• Physiologic role of Pentose

phosphate pathway

a.providing NADPH+H+ for biosyntheses

b.Providing ribose 5-phosphate for nucleotide

lack of G6PDH (erythrocyte hemolytic

anemia)

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五、生理意义 ①  非供能，提供生物合成所需的原料 a 、 5-P 核糖 b 、还原型 NADPH ⑴ 合成 FA ，类固醇激素，胆固

醇 ⑵ 维持体内一定量的 GSH ，保

持 RBC 的完整性，保护 SH 酶的活性

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NADPH+H+ NADP+

G-S-S-G GSH （ oxidation ） （ deoxidized ）

peroxides FA(unsaturated )

lysosome hydrolase release cell membrane hemolysis

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★ 遗传性 GPDH 缺乏症 蚕豆黄 c 、加单氧酶体系供氢体 参与生物转化 d 、 WBC 的杀菌作用，过氧化氢的 生成 2 、 3C ， 4C ， 5C ， 6C ， 7C 糖的互

变

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D. glycogenolysis

• concept

• the reaction site

• basic process

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E. glycogenesis

• concept

• the reaction site

• basic process

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F.The control of glycogenolysis

& glycogenesis

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G. gluconeogenesis

• concept

• the reaction site

• basic process

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HK PFK

G G6P G6F 1 ， 6 2P-F(FBP)

  3 PG BPG G3P

PK

PEP pyruvate

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ADP HK ATP

① G-6-P G

glucose-6-phosphatase

ADP PFK ATP

② 1 ， 6-2P-F G6F

fructose I,6-biphosphatase

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3. Phosphoenelpyruvate is formed from

pyruvate by way of oxaloacetate

(bypass of carboxylation of pyruvate)

Key enzyme:

pyruvate carboxylase

PEP carboxykinase

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• the key enzyme

• Physiologic role of

gluconeogenesis

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a.In a long period of

starvation

b.Reuse of lactate: cori’s

cycle

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c. Promote the excretion

of H+ in kidney

＃ lactic acidosis

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H+ PEP carboxykinase

0xaloacetate PEP Oxaloacetate ， α-ketoglutarate oxatoacetate

α-ketoglutarate ， Glu

NH3 NH3+H+ NH4 （ excrete ） Gln

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• gluconeogenesis &

glycolysis are reciprocally

regulated