mbs1- k3 - carbohydrate metabolism 1. new

7/27/2019 Mbs1- k3 - Carbohydrate Metabolism 1. New

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CARBOHYDRATE

METABOLISM

BIOCHEMISTRY

MEDICAL FACULTY USU


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Digestion and absorption Carbohydrate

1. Breakdown to monosaccharides

a. Mechanical digestion

b. Chemical digestion function of enzymes

2. Active transport process

3. Liver conversion of fructose and galactose toglucose

CARBOHYDRATE METABOLISM

CARBOHYDRATE METABOLISM


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GLYCOLIYSIS

The Embden Meyerhof Parnas Pathway

To provide energy (especially brain and RBC)

ATPIn the cytosol of all cells

Aerobic or anaerobic

In aerobic glycolysis :- glucose converted to two pyruvate

- sets the stage for pyruvate to acetyl CoA


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GLYCOLIYSIS

In anaerobic glycolysis

- In tissues: lack mitochondria or insufficient of

oxygen

- Pyruvate lactic acid (need NADH)

- Reoxidize the NADH

permitting glycolysis to proceed

Reactions of glycoliysis- First reaction Phosphorylation of glucose

by hexokinase or glukokinase


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PROPERTIES OF

HEXOKINASE AND GLUKOKINASE

Enzyme Hexokinase Glukokinase

Tissue distr. Most tissues Liver and cells

Km Low (0.1 mmol/L) High(10 mmol/L)

Vm Low High

Inhibition by

glucose 6 phosp

Yes No


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Comparison of relative enzymatic activities of

hexokinase and glucokinase over the physiological blood

Glc range


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GLYCOLIYSIS

Reactions of glycoliysis :

- Consist 3 irreversible reactions

Hexokinase or glucokinase

Phosphofructokinase

Pyruvate kinase

- Oxidation of glyceraldehyde 3 phosphate

the first oxidation reaction of glycolysis

by glyceraldehide 3 phosphatedehydrogenase

(NAD dependent)


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GLYCOLIYSIS

Reactions of glycoliysis :

-Arsenic is due competition with Pi in reaction form

3 phosphoglycerate

1 arseno 3 phosphoglyserate

- Fluoride inhibit Enolase


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GLYCOLIYSIS


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a. aerobically to acetyl Co A, acetyl Co A is

oxidized CO2 and H2O via the

citric acid cycle

b. anaerobically to lactate in muscle

and in certain micro-organisms or

c. anaerobically to ethanol(fermentation) microorganisms

Fates of Pyruvate


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Reduction of Pyruvate to Lactate


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Summary of Energy Relationships

for GlycolysisInput = 2 ATP

- glucose + ATP glucose-6-P

- fructose-6-P + ATP fructose 1,6 bisphosphate

Output= 4 ATP + 2 NADH

- 2 glyceraldehyde-3-P + 2 Pi + 2 NAD+

2 (1,3 bisphosphoglycerate) + 2 NADH

- 2 (1,3 bisphosphoglycerate) + 2 ADP2 (3-P-glycerate) + 2 ATP

- 2 PEP + 2 ADP 2 pyruvate + 2 ATP

Net = 2 ATP and 2 NADH


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ATP produced from complete oxidation of

1Glucose using aerobic respiration

38 ATPs are produced in eukaryotes.

Pathway

By substrate-level

phosphorylation

By oxidativephosphorylation

FromNADH FromFADH

Glycolysis 2 6 0

Intermediate

step

0 6

Krebs cycle 2 18 4

Total 4 30 4


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ATP produced from complete oxidation of 1

Glucose using aerobic respiration

Figure 24.5


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Regulation of Glycolysis

Allosteric enzymes : hexokinase, PFK 1, pyruvate

kinase

allosteric effectors : AMP, ATP, Citrate,Acetyl co A, Fructose 2,6 BP, Fructose 1,6 BP

Hormones : insulin, glucagon


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Synthesis of 2,3 Bisphosphoglycerate

In the red blood cells: 1,3 bisphosphoglycerate 2,3 bisphosphoglycerate (2,3 BPG) bybisphosphoglycerate mutase

2,3 BPG 3 phosphoglycerate (an intermediatein glycolysis)

Binds to hemoglobin, decreasing its affinity foroxygen

oxygen more readily available to tissue


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CLINICAL ASPECTS

Inhibition of pyruvate metabolism lacticacidosis

- Arsenic and mercuric ions react with the SHgroups of lipoic acid

- It inhibit pyruvate dehydrogenaseAldolase A and pyruvate kinase (PK) deficiencyhemolytic anemia

- Mature erythrocyte dependent on glycolysis forproduction of ATP

- Reduced rate glycolysis inadequate energy

the premature death and lysis of the red blood

cell

mbs1- k3 - carbohydrate metabolism 1. new

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