Introduction to Glycolysis for basic biochemistry

Introduction to Glycolysis for basic biochemistry

1. Glycolysis

2. Lesson Learning Outcome Upon c ompl e t i o n of this lec t u r e, should be able to: understand the glycolytic pathway fates of pyruvate students

3. Cellular Respiration Is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste product. The reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy in the process. Cell u lar r e s p i r a tion i s c o n side r ed an exothermic redox reaction which releases heat.

4. Overall cellular respiration

5. The Glycolytic Pathway Glucose is converted to two pyruvate

6. Gly c ol y sis

7. Glycolysis In cytoplasm, an anaerobic process which generates ATP, NAPH and pyruvate Glycolysis: a series of 10 enzyme-catalyzed reactions by which glucose is oxidized to two molecules of pyruvate – there is net conversion of 2ADP to 2ATP C 6 H 1 2 O 6 Glucose glycolysis O 2 C H 3 CC O O - Pyruvate + 2 H + + 2 A D P + 2 P i + 2 A T P C 6 H 1 2 O 6 Glucose O 2 CH 3 C C O O - Pyruvate

8. Fates of Pyruvate Pyruvate is most commonly metabolized in one of three ways, depending on the type of organism and the presence or absence of O 2 O CH 3 CC O O - Pyruvate OH CH 3 C H C O O - Lactate CH 3 CH 2 OH + CO 2 Ethanol 3 C O 2 + 2 H 2 O aerobic conditions plants and animals anaerobic conditions c o n t r a c t i n g m u s cl e anaerobic conditions f e r m e n t a t i o n i n y e a s t

9. Reactions of glycolysis R eaction 1 : p ho s pho r yl a t i o n of  - D -glu c o s e to give glucose-6-phosphate O H O H HO H O CH 2 OH O + - O - P - O - P - O - A M P O - O - ATP  -D-Glucose hexokinase M g 2 + O H HO H O CH 2 O PO 3 2 - O OH  - D - Gl u c o s e -6 - ph os ph a te + O - O - P - O - A M P O - ADP O O

10. – this reaction is driven by the free energy of hydrolysis of ATP T h es e t w o r eact i on a r e c ouple d , s o the o v e r all reaction is the sum of the two and is exergonic The enzyme that catalyzes this reaction is hexokinase Glu c o s e - 6 - pho s p h a t e inhibits h e x okina s e – f e e d ba c k inhibition

11. R e a c t i o n 2 : is o m e r i z a t i o n of glu c os e - 6 - phosph a t e to fructose-6-phosphate  -D-Glu Th e en z y me th a t c a t a l y z e s this r e a cti o n is glucosephosphate isomerase The aldehyde group at C1 is reduced to hydroxyl, and the C2-hydroxyl is oxidized to give the ketone group of fructose- 6-phosphate 2 3 6 CH OPO 2 - O H HO H O C H 2 O P O 3 O 2 - phosphogluco- isomerase 1 2 6

12. Reaction 3: phosphorylation of fructose-6-phosphate 1 CH 2 O H O H H O H HO  - D - Fr u c to s e -6 - ph os ph a t e 6 CH 2 O PO 3 2 - H O H + ATP phospho- fructokinase M g 2 + 2 3 1 CH 2 O PO 3 2 - O O H H H H O 6 CH O PO HO H  - D - Fr u c to s e -1 , 6 - b i s ph o s ph a t e The phosphorylation of fructose-6-phosphate is highly exergonic and irreversible – enzyme responsible is phosphofructokinase 2 - + ADP

13. Reaction 4: cleavage of fructose-1,6-bisphosphate to two triose phosphates by enzyme aldolase 2 C = O C H O P O 3 HO H H O H H O H CH 2 O P Fruct 2 - aldolase C H 2 O P O 3 2 - C = O C H 2 O H D i h y d r

14. Reaction 5: isomerization of triose phosphates catalyzed by triosephosphate isomerase r ea c tion i n v ol v es t w o succ e ss i v e k e t o - enol tautomerizations on l y t h e D e na n tiomer of gl y ce r alde h y d e 3 - phosphate is formed C H 2 O H C = O CH 2 OPO 3 2 - D i h y d r oxya ce t o n e phosphate CH O H C OH CH 2 OPO 3 2 - D - G l y c e r a l d e h y d e 3-phosphate CH O H C-OH CH 2 OPO 3 2 - An enediol i n t e r m e d i a t e

15. R ea c tion 6 : o xid a tion of the -CH O g r o u p of D - glyceraldehyde-3-phosphate the -CHO group is oxidized to a carboxyl group the oxidizing agent, NAD + , is reduced to NADH G- C- H + A two-electron oxidation O H 2 O G- C- OH O 2 H + 2 e - H + 2 e - N A D H A two-electron reduction + + + N AD + + O G - C - H + H 2 O + N A D + O G- C- OH H + +

16. the o v e r all r ea c tion i n v ol v es a n e x e r g oni c o xi d a tion and an endergonic phosphorylation the overall reaction is slightly endergonic  G o' = +49.3 kJ•mol -1  G o' = -43.1 kJ•mol -1 oxidation: phosphorylation: O C-O - O O C-H to C-O - O O O C - H to to C - O - P - O - O - O O C - O - P - O - O -  G o' = +6.2 kJ•mol -1

17. R e a c t ion 7 : t r a n s f er of a p h os ph at e g r o u p f r o m 1 ,3 - bisphosphoglycerate to ADP – this reaction is called substrate-level phosphorylation + 1 , 3 - B i s ph o s ph o - glycerate COO - H C O H CH 2 O P O 3 2 - 3 - P h o s ph og l y c e r a te C H O P O 2 3 2 - O C - O P O 3 2 - H C OH + O - O - P - O - A M P O - ADP phospho- glycerate kinase Mg 2+ - O - P - O - P - O - A M P O O O - O - ATP

18. the su m o f the ende r g on i c – this reaction is pho s ph o r y l a t i o n of ADP and the exergonic hydrolysis of the mixed phosphate anhydride phosphorylation:  G o' = -49.3 kJ•mol -1  G o' = +0.5 kJ•mol -1 O C-O - O O C - O - P - O - O - ADP + P i h y d r o l y s i s :  G o' = -18.8 kJ•mol -1 + P i A T P + H 2 O O O C - O - P - O - O - + ADP + P i O C-O - + ATP + H 2 O

19. Reaction 8: isomerization of 3-phosphoglycerate to 2-phosphoglycerate COO - H C O H CH 2 O P O 3 2 - 3- P h os ph og l y c e r ate COO - H C O P O 3 2 - CH 2 O H 2- P h os ph og l y c e r ate phosphoglycerate mutase

20. Reaction 9: dehydration of 2-phosphoglycerate 3 COO - H C O P O CH 2 O H 2- P h os p 2 - C O O - C enolase Mg 2+

21. Reaction 10 : phosphate transfer to ADP stage 1: transfer of the phosphate group COO - C O PO CH 2 3 2 - P h o s ph o e n o l - pyruvate + - O - P - O - P - O - A M P O - O - ATP COO - C - O H CH 2 E n ol of p y r u vate O - O - P - O - A M P O - ADP + pyruvate kinase Mg 2+ O O

22. Stage 2: enolization to pyruvate COO - C - O H CH 2 E n ol of p y r u va t e C O O - C = O CH 3 Pyruvate

23. Glycolysis Summing these 10 reactions gives the net equation for glycolysis C 6 H 1 2 O 6 Glucose + 2 N A D + + 2 H P O 4 2 - + 2 A D P gly c oly s i s O 2 CH 3 CC O O - Pyruvate + 2 N A D H + 2 A T P + 2 H 2 O + 2 H +

24. Energetics of Glycolysis Three reactions exhibit particularly large decreases in free energy; the enzymes that catalyze these reactions are sites of allosteric control hexokinase phosphofructokinase pyruvate kinase

25. Fructose is phosphorylated by fructokinase (liver) or hexokinase (adipose) on the 1 or 6 positions resp. Fructose-6-phosphate is an intermediate of glycolysis. Fructose-1-phosphate is acted upon by an aldolase- like enzyme that gives DHAP (dihydroxyacetone phosphate) and glyceraldehyde. DHAP is a glycolysis intermediate and glyceraldehyde can be phosphorylated to glyceraldehyde-3-P. Glycerol is phosphorylated to G-3-P which is then converted to glyceraldehyde 3 phosphate.

26. Galactose has a slightly complicated multi-step pathway for conversion to glucose-1-phosphate. gal gal-1-P UDP-gal UDP-glc glc-1-P. If this pathway is disrupted because of defect in one or more enzymes involved in the conversion of gal to glc-1-P, then galactose accumulates in the blood and the subject suffers from galactosemia which is a genetic disorder, an inborn error of metabolism.

27. Reactions of Pyruvate Pyruvate does not accumulate in cells, but rather undergoes one of three enzyme- catalyzed reactions, depending of the type of cell and its state of oxygenation reduction to lactate reduction to ethanol oxidation and decarboxylation to acetyl-CoA

28. Lactate Fermentation ⦿ In vertebrates under anaerobic conditions, the most important pathway for the regeneration of NAD + is reduction of pyruvate to lactate lactate dehydrogenase (LDH) is a tetrameric isoenzyme consisting of H and M subunits; H 4 predominates in heart muscle, and M 4 in skeletal muscle O CH CCOO - + NADH + H + 3 P y r u v a t e OH CH 3 CHCOO - + NAD + Lactate lactate d e h y d r o g e n a s e

29. Pyruvate to Lactate while lactate fermentation allows glycolysis to continue, it increases the concentration of lactate and also of H + in muscle tissue when blood lactate reaches about 0.4 mg/100 mL, muscle tissue becomes almost completely exhausted C 6 H 1 2 O 6 Gluco O H lactate fermentation

30. Pyruvate to Ethanol Yeasts and several other organisms regenerate NAD + by this two-step pathway; decarboxylation of pyruvate to acetaldehyde 3 Pyruvate O pyruvate decarboxylase O CH C COO - + H + 3 O CH CH + NADH + reduction of acetaldehyde to ethanol alcohol H + A c e t a l d e h y d e d e h y d r og e n a s e CH 3 CH 2 OH + Ethanol NAD +

31. Pyruvate to Acetyl-CoA U n de r ae r ob i c c o ndit i o n s , p y ru v a t e u n de r g oes oxidative decarboxylation the carboxylate group is converted to CO 2 the remaining two carbons are converted to the acetyl group of acetyl-CoA 3 P y r u va te O CH 3 CSCoA + Acetyl-CoA C O 2 + N A D H oxidative decarboxylation O CH C COO - + N A D + + C o A S H

32. End of lecture