1. Glycolysis

2. To recognize the sole energy producing pathway (glycolysis) in RBCs
To understand the different reactions of glycolysis
To know what specifies glycolysis in RBCS.
To retrieve the importance of 2,3,BPG
To know how specific metabolism of RBCs suits its function

3. Glycolysis is the sequence of reactions that convert glucose into pyruvate (or lactate) with the concomitant production of small amount of ATP

4. Glycolysis occurs in the cytosol
Glycolysis occurs in all tissues
Glycolysis can proceed either in presence and in absence of O2

5. Glycolysis Two phases:
First phase; Energy–investment phase (preparatory): converts glucose (6 C) to two Glyceraldehyde-3-P (3 C)

6. Glycolysis Two phases:
-Second phase; Energy–generation phase (pay off): produces two pyruvates or two lactates

7. RX1: Hexose Kinase 1st step in glycolysis
This is a priming reaction - ATP is consumed here in order to get more later

8. Rx 2: Phosphoglucoisomerase
Reversible reaction

9. Rx 3: Phosphofructokinase PFK is the committed step in glycolysis!
The second priming reaction of glycolysis
Committed step means PFK is highly regulated

10. Phosphofructokinase is highly regulated
ATP inhibits PFK, AMP reverses inhibition
PFK increases activity when energy status is low
PFK decreases activity when energy status is high

11. Reaction 4: Aldolase I Hexose cleaved to form two trioses,
Reversible Reaction
C1 thru C3 of F1,6-BP -> dihydroxyacetone phosphate
C4 thru C6 -> Glyceraldehyde 3 phosphate

12. Reaction 4: Aldolase I

13. Rx 5: Triose Phosphate Isomerase (TPI)
Reversible rxn
Conversion of DHAP to G-3-P by TPI maintains steady state [G-3-P]

14. Any Questions

15. Glycolysis - Second Phase
In this phase, 2 G-3-P are converted to 2 pyruvates (aerobic) or 2 lactates (anaerobic)

16. Glycolysis - Second Phase
Second phase involves two very high energy phosphate intermediates
1,3 BPG
Phosphoenolpyruvate

17. Glycolysis - Second Phase
Substrate level energy (phosphorylation) production of 4 ATP (2 X 2 ATP from each 3C molecule)
Net ATP yield for glycolysis is 4-2 = 2 ATP

18. Rx 6: Glyceraldehyde-3P-Dehydrogenase
G3P is oxidized and phosphorylated to 1,3-BPG
Reversible rxn
Pi is used as phosphate donor
Production 1 NADH + H+ (3 ATP from Respiratory Chain aerobically but not in RBCs)

19. Rx 6: Glyceraldehyde-3P-Dehydrogenase
NADH generated in this reaction is re-oxidized by respiratory electron transport chain (generates 3 ATP) but NOT in RBCs.
ETC will regenerate NAD for more glycolysis to run but NOT in RBCs.
If no ETC, transfer of pyruvate to lactate is needed.

20. Rx 7: Phosphoglycerate Kinase (PGK)
ATP synthesis from a high-energy phosphate
This is referred to as "substrate-level phosphorylation“

21. Rx 8: Phosphoglycerate Mutase
Phosphoryl group moves from C-3 to C-2
Mutases are isomerases that transfer phosphates from one hydroxyl to another

22. Rx 9: Enolase Reversible rxn
"Energy content" of 2-PG and PEP are similar
Enolase just rearranges to a form a compound from which energy can be released in hydrolysis

23. Rx 10: Pyruvate Kinase
Substrate level phosphorylation generates second ATP
Regulatory step
Allosterically activated by AMP, F-1,6-bisP
Allosterically inhibited by ATP and acetyl-CoA

24. Rx 10: Pyruvate Kinase
Substrate level phosphorylation generates second ATP
Hereditary deficiency of pyruvate kinase causes hemolytic anemia as it decreases the net ATP yield of glycolysis in RBCs especially if 2,3,BPG is produced.

25. Fates of Pyruvate

26. Lactate formation   
Under anaerobic conditions pyruvate is converted to lactate by the enzyme lactate dehydrogenase
Important for the regeneration of NAD+ under anaerobic conditions.

27. Lactate forming cells
Cells of lens and cornea of the eye, kidney medulla, testes, leukocytes, and RBCs, because these tissues are all poorly vascularized and/or lack mitochondria.
2.In exercising skeletal muscle.

28. Lactate utilization:
The direction of the lactate dehydrogenase reaction depends on:
the relative intracellular conc.of pyruvate and lactate.
the ratio of NADH/NAD+ in the cell.
In the liver, heart and CNS, the ratio of NADH/NAD+ is lower than in exercising muscle.
These tissues oxidize lactate (obtained from the blood) to pyruvate.
In the liver, pyruvate is either converted to glucose by gluconeogenesis or oxidized in the TCA cycle.
Heart muscle and CNS oxidizes lactate to CO2 and H2O via the TCA cycle.