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Mia Kusmiati Departemen Biokimia FK UNISBA. Carbohydrates Carbohydrates are called carbohydrates because they are essentially hydrates of carbon (i.e.

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Presentation on theme: "Mia Kusmiati Departemen Biokimia FK UNISBA. Carbohydrates Carbohydrates are called carbohydrates because they are essentially hydrates of carbon (i.e."— Presentation transcript:

1 Mia Kusmiati Departemen Biokimia FK UNISBA

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3 Carbohydrates Carbohydrates are called carbohydrates because they are essentially hydrates of carbon (i.e. they are composed of carbon and water and have a composition of (CH 2 O) n. The major nutritional role of carbohydrates is to provide energy and digestible carbohydrates provide 4 kilocalories per gram. No single carbohydrate is essential, but carbohydrates do participate in many required functions in the body.

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9 Glycolysis Glycolysis What is glycolysis?  Ten step metabolic pathway to convert glucose into two molecules of pyruvate and two molecules each of NADH and ATP.  All carbohydrates to be catabolized must enter the glycolytic pathway. - Glycolysis is central in generating both energy and metabolic intermediaries.

10  Major anaerobic pathway in all cells  NAD + is the major oxidant  Requires PO 4  Generates 2 ATP’s per glucose oxidized  End product is lactate (mammals) or ethanol (yeast)  Connects with Krebs cycle via pyruvate

11 Phase I. Energy Investment. 1- Glucose is phosphorylated. Glucose enters a cell through a specific glucose transport process. It is quickly phosphorylated at the expense of an ATP. The investment of an ATP here is called “priming.” hexokinase Enzymes = hexokinase or glucokinase Isomerization of glucose 6-phosphate phosphoglucoisomerase Enzyme = phosphoglucoisomerase

12 glucose 6-phosphate fructose 6-phosphate aldose to ketose isomerization reversible,  G  = 1.7 kJ/mole

13 3- Second phosphorylation phosphofructokinase Enzyme = phosphofructokinase -second ATP investment -highly exergonic, essentially irreversible,  G°´= kJ/mole regulated - highly regulated, modulating carbon flux through glycolysis in response to energy and carbon requirements fructose 1,6 bisphosphate ATP ADP

14 4- Cleavage to two triose phosphates aldolase Enzyme = aldolase glyceraldehyde dihydroxyacetone 3-phosphate phosphate 3-phosphate phosphate where P = phosphate  cleaves a 6C sugar to 2 3C sugars   G°´= kJ/mole, driven by next Rx. HC=O H 2 COP HCOH O=C HCOP + CH 2 OH H

15 5-Isomerization of Dihydroxyacetone phosphate triose-phosphate isomerase Enzyme = triose-phosphate isomerase H 2 C-OH C=O CH 2 -O- P dihydroxyacetone glyceraldehyde phosphate 3-phosphate

16 5-Isomerization of Dihydroxyacetone phosphate triose-phosphate isomerase Enzyme = triose-phosphate isomerase H 2 C-OH C=O CH 2 -O- P dihydroxyacetone glyceraldehyde phosphate 3-phosphate

17  allows interconversion of two triose phosphate products of aldolase cleavage  only glyceraldehyde 3-phosphate can be used further in glycolysis.  aldose-ketose isomerization similar to phosphoglucoisomerase rxn  allows dihydroxyacetone phosphate to be metabolized as glyceraldehyde 3-phosphate  reversible,  G  ´= +7.5 kJ/mole. This is important in gluconeogenesis

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19 6- Oxidation of glyceraldehyde 3-phosphate Enzyme= glyceraldehyde-3-phosphate dehydrogenase + -addition of phosphate, oxidation, production of NADH, formation of high energy compound glyceraldehyde 3-phosphate 1,3 bisphosphoglycerate O HOPO OH NAD NADH O OPOH C=O O - HCOH H 2 C O- P

20 7- Transfer of phosphate to make ATP Enzyme = phosphoglycerate kinase - first substrate level phosphorylation, yielding ATP - 2 1,3 bis PG yield 2 ATPs, thus so far ATP yield = ATP input - high free energy yield,  G°´= kJ/mole drives several of the previous steps. O=C-O- P O=C-OH P HC-OH + P HC-OH + P H 2 C-O-P P Adenosine Adenosine 1,3PG ADP 3-phosphoglycerate ATP

21 8- Phosphate shift setup Enzyme= phosphoglycerate mutase - shifts phosphate from position 3 to 2 - reversible, ΔG  = kJ/mole

22 9- Generation of second very high energy compound Enzyme = enolase -- little energy change in this reaction, ΔG  = +1.7 kJ/mole because the energy is locked into enolphosphate

23 10- Final generation of ATP Enzyme = pyruvate kinase P O H ADP ATP O - OOC-C=CH - OOC-C-CH 3 phosphoenolpyruvate pyruvate -second substrate level phosphorylation yielding ATP - highly exergonic reaction, irreversible, ΔG  = kJ/mole.

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28  6-phosphofructokinase-1 Allosteric enzyme negative allosteric effectors Citrate, ATP Positive allosteric effectors AMP, fructose1,6-bisphosphate, fructose2,6- bisphosphate Changes in energy state of the cell (ATP and AMP)

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30  Pyruvate Kinase  Allosteric enzyme Inhibited by ATP.  Isoenzyme in liver activated by fructose 1,6 bisphosphate inhibited by alanine  Regulated by phosphorylation and dephosphorylation  Hexokinase  Different isoenzymes Hexokinase IV glucose 6-phosphate is an allosteric inhibitor promote biosynthesis

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32  Glycolysis is the emergency energy-yielding pathway  Main way to produce ATP in some tissues red blood cells, retina, testis, skin, medulla of kidney  In clinical practice

33  Glucose oxidation 1. Oxidation of glucose to pyruvate in cytosol 2. Oxidation of pyruvate to acetylCoA in mitochondria 3. Tricarboxylic acid cycle and oxidative phosphorylation


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