1. Carbohydrate Catabolism
Figure 24.5

2. Glycolysis

3. Glycolysis Start materials End products Arrow type No. of reactions
Type of reactions
Enzyme name for each reaction
Condition of each reaction
Intermediates name and No. of there carbon
Functional group of each metabolites
ATP production/ consumption

4. Glycolysis Start materials End products Arrow type No. of reactions
Type of reactions
Enzyme name for each reaction
Condition of each reaction
Intermediates name and No. of there carbon
Functional group of each metabolites
ATP production/ consumption

5. Glycolysis What is the overall pathway in glycolysis?
How is the 6-carbon glucose converted to the 3-carbon glyceraldehyde-3-phosphate?
How is glyceraldehyde-3-phosphate converted to pyruvate?
How is pyruvate metabolized anaerobically?
Where are the control points in the glycolytic pathway?
How much energy can be produced by glycolysis?

6. Glycolysis Definition Location Reaction of glycolysis
Glycolysis is the sequence of reactions that converts glucose into pyruvate in the presence of oxygen (aerobic) or lactate in the absence of oxygen (anaerobic) with the production of ATP
Location
Glycolysis is the major pathway for the utilization of glucose and is found in cytosol of all cells
Reaction of glycolysis
The breakdown of glucose to pyruvate is brought about by sequential action of 10 enzymes which can be divided into two phases
First phase, energy requiring phase or preparative phase
Second phase, energy generating phase pay off phase

7. Glycolysis A three-phase pathway in which:
Glucose is oxidized into pyruvic acid (PA)
It loses 2 pairs of hydrogens
NAD+ is reduced to NADH + H+
It accepts 2 pairs of hydrogens lost by glucose
ATP is synthesized by substrate-level phosphorylation
Pyruvic acid: end-product of glycolysis
Moves on to the Krebs cycle in an aerobic pathway (i.e. sufficient oxygen available to cell)
Is reduced to lactic acid in an anaerobic environment (insufficient O2 available to cell)
pyruvic acid lactic aicd

8. Glycolysis: Phase 1 and 2 Phase 1: Sugar activation
Two ATP molecules activate glucose into fructose-1,6-diphosphate
The 1 and 6 indicate which carbon atom to which they are attached.
Phase 2: Sugar cleavage (splitting)
Fructose-1,6-bisphosphate (6 C’s) is split into two 3-carbon compounds:
Glyceraldehyde 3-phosphate (GAP)

9. Glycolysis: Phase 3 Phase 3: Oxidation and ATP formation
The 3-carbon sugars are oxidized (reducing NAD+); i.e., 2 H’s + NAD NADH2
Inorganic phosphate groups (Pi) are attached to each oxidized fragment
The terminal phosphates are cleaved and captured by ADP to form four ATP molecules
The final products are:
Two pyruvic acid molecules
Two NADH + H+ molecules (reduced NAD+)
A net gain of two ATP molecules

10. Stage 1
Glucose
F-1,6-BP
Stage 2
DHAP
GAP
Stage 3 2X
PEP
Pyruvate

11. Glycolysis

12. The overall pathway of glycolysis
Glycolysis is the first stage of glucose metabolism
One molecule of glucose is converted to fructose-1,6-bisphosphate, which gives rise to two molecules of pyruvate
Glycolysis plays a key role in the way organisms extract energy from nutrients
Once pyruvate is formed, it has one of several fates

13. The reactions of glycolysis
What are the reaction of glycolysis?
In glycolysis, glucose is converted to pyruvate in a multistep pathway.
Glucose is converted to pyruvate in a series of 10 reactions, only one of which is an oxidation

14. The reactions of glycolysis (cont’d)
Phosphorylation of glucose to give glucose-6-phosphate
Isomerization of glucose-6-phosphate to give fructose-6-phosphate
Phosphorylation of fructose-6-phosphate to yield fructose-1,6-bisphosphate
Cleavage of fructose-1,6,-bisphosphate to give glyceraldehyde-3-phosphate and dihyroxyacetone phosphate
Isomerization of dihyroxyacetone phosphate to give glyceraldehyde-3-phosphate

15. The reactions of glycolysis (cont’d)
Oxidation of glyceraldehyde-3-phosphate to give 1,3-bisphosphoglycerate
Transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP to give 3-phosphoglycerate
Isomerization of 3-phosphoglycerate to give 2-phosphoglycerate
Dehydration of 2-phosphoglycerate to give phosphoenolpyruvate
Transfer of a phosphate group from phosphoenolpyruvate to ADP to give pyruvate

16. Conversion of glucose to glyceraldehyde-3-phosphate (preparation phase) of glycolysis
In step 1 of glycolysis, glucose is phosphorylated to give glucose-6-phosphate
G6P is an intermediate in several metabolic pathway
The reaction is endergonic, as it is driven by the free energy of hydrolysis of ATP
The kinase is ATP dependent enzymes that transfer a phosphate group from ATP to a substrate
hexokinas
Glucokinase
This reaction is irreversible (control point)

17. Conversion of glucose to glyceraldehyde-3-phosphate (cont,d)
The second step is the isomerization of glucose-6-phosphate to fructose-6-phosphate
The C-1 aldehyde of glucose-6-phosphate is reduced to a hydroxyl group
The C-2 hydroxyl group is oxidized to give the ketone group of fructose-6-phosphate
There is no net redox reaction
Isomerase is an enzyme that catalyzes the structural rearrangement of isomer

18. Conversion of glucose to glyceraldehyde-3-phosphate (cont,d)
Step 3
Fructose-6-phosphate is then phosphorylated by ATP again to generate fructose-1,6-bisphosphate
This is the second reaction to be coupled to ATP hydrolysis
This is the key point reaction (F1,6BP key intermediate)
This reaction is irreversible (control point)

19. Conversion of glucose to glyceraldehyde-3-phosphate (cont,d)
In step 4 Fructose-1,6-bisphosphate is split into two 3-carbon fragments
Reaction catalyzed by aldolase
Side chains of an essential Lys and Cys play key roles in catalysis the reaction
aldolase

20. Conversion of glucose to glyceraldehyde-3-phosphate (cont,d)
In step 5, dihydroxyacetone phosphate (DHAP) is converted to glyceraldehyde-3-phosphate
These compounds are trioses

21. Summary
In the first stages of glycolysis, glucose is converted to two molecules of glyceraldehyde-3-phosphate
The key intermediate in this series of reactions is fructose-1,6-bisphosphate. The reaction that produces this intermediate is a key control point of the pathway, and the enzyme that catalyzes it, phosphofructokinase, is subject to allosteric control

22. Glyceraldehyde-3-Phohsphate is Converted to Pyruvate (pay off phase)
Step 6
The first reaction that begins the conversion to pyruvate involves the oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate
This reaction involves addition of a phosphate group, as well as an electron transfer reaction
The oxidizing agent, NAD+, is reduced to NADH
Dehydrogenase is an enzyme that oxidizes a substrate by transferring one or more hydrides (H-) to an acceptor, usually NAD+/NADP+ or FAD/FMN

23. Oxidation and Phosphorylation Reaction

24. Oxidation and Phosphorylation Reaction

25. Glyceraldehyde-3-Phohsphate is Converted to Pyruvate (Cont’d)
1,3-bisphosphoglycerate is converted to 3 phosphoglycerate
This step (step 7) involves another reaction in which ATP is produced by phosphorylation of ADP
1,3-bisphosphoglycerate transfers a phosphate group to ADP. This is known as substrate-level phosphorylation
Reaction is catalyzed by phosphoglycerate kinase
This reaction is the sum of the endergonic phosphorylation of ADP and the exergonic hydrolysis of the mixed phosphate anhydride

26. Glyceraldehyde-3-Phohsphate is Converted to Pyruvate (Cont’d)
The next step (step 8) involves the isomerization of 3-phosphoglycerate to 2-phosphoglycerate
The phosphate group is transferred from carbon 3 to carbon 2 of the glyceric acid backbone
This reaction is catalyzed by phosphoglyceromutase
Mutase is an enzyme that catalyzes the intramolecular shift of a chemical group from one position to another within the same molecule such as phosphoryl group

27. Glyceraldehyde-3-Phohsphate is Converted to Pyruvate (Cont’d)
Next, (step 9) 2-phosphoglycerate loses one molecule of water, producing phosphenolpyruvate
Enolase catalyzes the dehydration reaction (-H2O) and requires a Mg2+ as a cofactor
Phosphoenolpyruvate contains a high energy bond
enolase

28. Glyceraldehyde-3-Phohsphate is Converted to Pyruvate (Cont’d)
Phosphenolpyruvate (PEP) transfers its phosphate group to ADP, producing ATP and pyruvate
Reaction is catalyzed by pyruvate kinase
The double bond shift to the oxygen on carbon 2 and a hydrogen shifts to carbon 3
This reaction is irreversible (control point)

29. Summary
In the final stages of glycolysis, two molecules of pyruvate are produced for each molecule of glucose that entered the pathway
These reactions involve electron transfer (redox step 6), and the net production of two ATP for each glucose
There are three control points in the glycolytic pathway

30. Glucose and other monosaccharides Enzyme location cytosol
Entering substrates
Glucose and other monosaccharides
Enzyme location
cytosol
Net ATP production
2 ATP / glucose enter the pathway
Coenzyme production
2NADH + 2H+ formed under aerobic conditions
Final products
under aerobic conditions
Pyruvate
under anaerobic conditions
Lactate
Net reaction
Aerobic:
Anaerobic:

31. Fates of pyruvate from glycolysis

32. Anaerobic Metabolism of Pyruvate
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; H4 predominates in heart muscle, and M4 in skeletal muscle

33. The conversion of pyruvate to lactate in muscles
NAD+ Needs to be Recycled to Prevent Decrease in Oxidation Reactions
So NAD + will be present for further glycolysis to take place

34. Alcoholic Fermentation
Two reactions lead to the production of ethanol:
Decarboxylation of pyruvate to acetaldehyde
Reduction of acetaldehyde to ethanol
Pyruvate decarboxylase is the enzyme that catalyzes the first reaction
This enzyme require Mg2+ and the cofactor, thiamine pyrophosphate (TPP)
Alcohol dehydrogenase catalyzes the conversion of acetaldehyde to ethanol

35. Alcoholic fermentation
NAD+ Needs to be Recycled to Prevent Decrease in Oxidation Reactions
So NAD + will be present for further glycolysis to take place

37. Summary
Pyruvate is converted to lactate in anaerobic tissues, such as actively metabolizing muscle. NAD+ is recycled in the process
In some organisms, pyruvate is converted to ethanol in a process requiring thiamine pyrophosphate as a coenzyme

38. Control Points in Glycolysis
Three reactions exhibit particularly large decreases in free energy; the enzymes that catalyze these reactions are sites of allosteric control
Hexokinase (step 1)
Phosphofructokinase (step 3)
Pyruvate kinase (step 10)

39. Energy yield from glycolysis
The ATP yield from glycolysis is different in anaerobic and aerobic conditions
During aerobic (oxygen plenty) condition, the two NADH generated in step 6 can enter the mitochondrial electron transport chain to complete oxidation
As each NADH provides 3ATPs, this reaction provides 3 x 2 = 6 ATPs
The net gain of energy from glycolysis pathways is 8 ATPs

40. Energy yield (number of ATP generated) per molecule of glucose in the glycolytic pathway, under aerobic conditions (oxygen is available)
Step
Reaction
Enzyme
Source
No. of ATPs gained /glucose molecule 1
Hexokinase -
- 1 3
Posphofructokinase 6
Glyceraldehyde-3-phosphate dehydrogenase
NADH
3 X 2 = 6 7
1,3-bisPhosphoglycerate kinase
ATP
1 x 2 = 2 10
Pyruvate kinase
Total = 10 minus 2 = 8

41. Energy yield from glycolysis (cont’d)
But when oxygen is in deficiency (anaerobic condition)one molecule of glucose is converted to two molecule of lactate, the net yield of 2 molecules of ATP
4 molecules of ATP are synthesised by the 2 substrate level phosphorylation (steps 7 and 10)
But 2 ATP molecules are used in the steps 1 and 3, the net yield is only 2 ATP

42. Energy yield (number of ATP generated) per molecule of glucose in the glycolytic pathway, under anaerobic conditions (oxygen deficiency)
Step
Enzyme
Source
No. of ATPs gained /glucose molecule 1
Hexokinase -
- 1 3
Posphofructokinase 7
1,3-bisPhosphoglycerate kinase
ATP
1 x 2 = 2 10
Pyruvate kinase
Total = 4 minus 2 = 2

43. Glucosephosphate isomerase 2
ATP 1
Hexokinase
G-6-P
Glucosephosphate isomerase 2
F-6-P
ATP 3
Phosphofructokinase
F-1,6-BP 4
Aldolase
Triosphosphate isomerase
DHAP
GA3P 5 6
Glyceraldehyde-3-phosphate dehydrogenase
1,3BPG
ATP
NADH 7
3-Phosphoglycerate kinase
3-PG 8
Phosphoglyceromutase
2-PG 9
Enolase
PEP
ATP 10
Pyruvate kinase
Pyruvate

44. What did you learn?
Answer the following questions regarding glycolysis and energy.
What is the overall energy yield in ATP production when one molecule of glucose is converted to pyruvate?
Based on free energy yield, predict the reactions that are irreversible or poorly reversible in the glycolysis pathway.
Why is the phosphoglycerate kinase reaction reversible? What about the other kinase reactions?
Explain why G-6-P is ismerized to F-6-P, which then phosphorylated again to fructose F1,6-bP utilizing another ATP

45. Practice 4
Q 4 During glycolysis, a 6-carbon sugar diphosphate molecule is split into two 3-carbon sugar phosphate molecules.
A) True
B) False
Q 5 Under aerobic conditions, the end-product of glycolysis is further reduced to yield more ATP.

46. Answer to practice 4
Q 4 During glycolysis, a 6-carbon sugar diphosphate molecule is split into two 3-carbon sugar phosphate molecules.
A) True
B) False
Q 5 Under aerobic conditions, the end-product of glycolysis is further reduced to yield more ATP.

47. Practice 1
Q 1 In glycolysis, glucose is converted to A) CO2 and H2O. B) pyruvate. C) citrate. D) acetyl coA. E) NAD+ and ADP.

48. Practice 2
Q 2 The NET result of a single glycolysis run is the formation of
A) 1 NADH and 1 ATP.
B) 2 NADH and 2 ATP.
C) 2 NADH and 4 ATP.
D) 4 NADH and 2 ATP.
E) 4 NADH and 4 ATP.

49. Answer to practice 2
Q 2 The NET result of a single glycolysis run is the formation of
A) 1 NADH and 1 ATP.
B) 2 NADH and 2 ATP.
C) 2 NADH and 4 ATP.
D) 4 NADH and 2 ATP.
E) 4 NADH and 4 ATP.

50. Practice 3
Q 3 Under anaerobic conditions, the end-product of glycolysis is converted to
A) CO2 and H2O.
B) amino acids.
C) lactic acid.
D) hydrochloric acid.
E) acetic acid.

51. Answer to practice 3
Q 3 Under anaerobic conditions, the end-product of glycolysis is converted to
A) CO2 and H2O.
B) amino acids.
C) lactic acid.
D) hydrochloric acid.
E) acetic acid.