1. Glycolysis and Gluconeogenesis

2. Glycolysis What is glycolysis?
sequence of reactions that converts one molecule of glucose to two molecules of pyruvate with the formation of two ATP molecules
anaerobic

3. Glycolysis Why is glucose such a commonly used fuel?
tends to exist in ring form, very stable, doesn’t generally glycosylate proteins
formed from formaldehyde under prebiotic conditions

4. Glycolysis
What are the possible fates of glucose?

5. Glycolysis
What’s the difference between a facultative anaerobe and an obligate anaerobe?
Can you give an example of habitat-dependent anaerobiosis?
What about activity-dependent anaerobiosis?

6. Glycolysis
All the intermediates in glycolysis have either 3 or 6 carbon atoms
All of the reactions fall into one of 5 categories
phosphoryl transfer
phosphoryl shift
isomerization
dehydration
aldol cleavage

7. Glycolysis Entire reaction sequence may be divided into three stages
glucose is trapped and destabilized
six carbon molecule is split into two three carbon molecules
ATP is generated

8. Glycolysis – Stage 1 glucose converted to glucose-6-PO4 ATP is needed
catalyzed by hexokinase or glucokinase
induced fit
G01= -4.0 kcal/mole

9. Glycolysis – Stage 1 phosphoglucoisomerase
aldose is converted to ketose
G01=+0.4 kcal/mole

10. Glycolysis – Stage 1 rate limiting enzyme – allosteric
inhibited by high ATP, citric acid, long-chain fatty acids
stimulated by ADP or AMP
G01= kcal/mole

11. Glycolysis

12. Glycolysis – Stage 2
six carbon molecule split into 2- 3 carbon molecules
aldose and ketose
G01= kcal/mole

13. Glycolysis – Stage 3
At equilibrium most mixture exists as dihydroxyacetone phosphate
G01= kcal/mole

14. Triose Phosphate Isomerase

15. Glycolysis – Stage 3 redox reaction
energy from redox used to form acyl phosphate
G01= +1.5 kcal/mole

16. Glycolysis – Stage 3
Consists of two coupled processes

17. Glycolysis – Stage 3
formation of ATP – substrate level phosphorylation

18. Glycolysis – Stage 3
phosphoryl shift – uses 2,3 bisphosphoglycerate G01= +1.1 kcal/mole
dehydration G01 = +.44 kcal/mole
phosphoryl transfer G01 = -7.5 kcal/mole

19. Glycolysis

20. Fate of Pyruvate

21. Alcoholic Fermentation
Which organisms carry out this process?
yeast
other microorganisms
PDC requires thiamine pyrophosphate as coenzyme
NAD+ is regenerated

22. Lactic Acid Fermentation
Occurs in muscle cells, microorganisms
Regenerates NAD+

23. NAD+ and Dehydrogenases
Various dehydrogenases have a similar binding domain for NAD+ showing their common origin
Rossman fold

24. Glycolysis
How can fructose be used for energy?

25. Glycolysis
To use galactose it must be converted to glucose-6-PO4

26. Glycolysis

27. Glycolysis
What causes lactose intolerance?

28. Glycolysis What is galactosemia? inability to metabolize galactose
missing galactose 1-phosphate uridyl transferase
liver disease
development of cataracts
CNS malfunction

29. Control of Glycolysis Of what value is glycolysis for cells?
provides energy in form of ATP
provides building blocks for synthetic reactions
Where are most control points found?
enzymes that catalyze irreversible reactions
hexokinase
phosphofructokinase
pyruvate kinase

30. Phosphofructokinase
Most important control point in mammalian glycolytic pathway
allosteric enzyme
activated by AMP and fructose 2,6 bisphosphate
inhibited by high levels of ATP, citrate, fatty acids

31. Phosphofructokinase

32. Hexokinase Hexokinase is inhibited by its product glucose-6-PO4
glucose remains in blood
Glucokinase, an isozyme of hexokinase is not inhibited by glucose-6-PO4
found in liver
has lower affinity for glucose

33. Pyruvate Kinase Pyruvate kinase exists as isozymes
L form – predominates in liver
M form – mostly in muscle and brain
PK is an allosteric enzyme
activated by fructose 1,6 bisphosphate
inhibited by ATP, alanine
L form of PK influenced by covalent modification
inhibited by phosphorylation

34. Pyruvate Kinase

35. Glucose Transport
What is the role of glucose transporters in animal cells?
facilitate movement of glucose across cell membrane
What kind of molecule is a transporter and where is it located?
small protein embedded in plasma membrane

36. Glucose Transport
mammalian glucose transporter

37. Glucose Transport

38. Glycolysis and Cancer
Why are rapidly growing tumor cells dependent upon glycolysis?
insufficient oxygen supply
What is the function of HIF-1?
hypoxia-inducible transcription factor stimulates synthesis of many glycolytic enzymes and GLUT-1 and 3
also stimulates vascular endothelial growth factor

39. Gluconeogenesis What is gluconeogenesis?
synthesis of glucose from non-carbohydrate precursors
Why is this an important pathway?
What are some of the major precursors?
lactate, amino acids, glycerol
Where does this process occur?
liver, kidney

40. Gluconeogenesis
If gluconeogenesis involves the conversion of pyruvate to glucose why is it not simply the reverse of glycolysis?
glycolysis contains several irreversible reactions
Which reactions in glycolysis are irreversible?
phosphoenolpyruvate to pyruvate
fructose 6-phosphate to fructose 1,6-bisphosphate
glucose to glucose 6-phosphate

41. Gluconeogenesis
What is the first reaction?

42. Gluconeogenesis Why is pyruvate carboxylase of special interest?
structural properties
contains ATP-grasp domain at N-terminal end
contains biotin-binding domain at C-terminal end

43. Gluconeogenesis What is the role of biotin in this reaction?
prosthetic group lined to -amino group of lysine residue
carrier of activated carbon dioxide

44. Gluconeogenesis Pyruvate carboxylase is an allosteric enzyme
activated by acetyl CoA
needed to form carboxybiotin

45. Gluconeogenesis
Carboxylation of pyruvate occurs in the mitocondria but next step in reaction sequence occurs in cytosol

46. Gluconeogenesis Decarboxylation of oxaloacetate is coupled with
phosphorylation by GTP
enzyme is phosphoenolpyruvate carboxykinase

47. Gluconeogenesis Which other steps in glycolysis are irreversible?
conversion of fructose 1,6-bisphosphate to fructose 6-phosphate
conversion of glucose 6-phosphate to glucose

48. Gluconeogenesis G° = -16.7 kJ mol-1
fructose-1,6-bisphosphatase is an allosteric enzyme, inhibited by AMP and activated by ATP

49. Gluconeogenesis
Enzyme that catalyzes last reaction not found in all tissues
liver and kidney cortex

50. Gluconeogenesis
Is gluconeogenesis an energetically favorable reaction in the cell?
What drives this reaction?
Are glycolysis and gluconeogenesis active at the same time?

51. Regulation of Glycolysis and Gluconeogenesis
What are some of the factors that ensure the reciprocal regulation of these processes?
allosteric regulators of key enzymes
energy charge
fructose 2,6-bisphosphate
hormones

52. Regulation of Glycolysis and Gluconeogenesis

53. Regulation of Glycolysis and Gluconeogenesis
fructose 2,6-bisphosphate stimulates PFK and inhibits fructose 1,6-bisphosphase
controlled by insulin and glucagon and reflects the nutritional status of the cell

54. Regulation of Glycolysis and Gluconeogenesis
How do hormones influence the enzymes associated with these processes?
influence gene expression
change transcription rate
influence degradation of m-RNA
insulin PFK, PK
glucagon PEPCK, fructose 1,6-bisphosphatase

55. Regulation of Glycolysis and Gluconeogenesis
What are substrate cycles and why are they important?
can amplify metabolic signals
can generate heat

56. Regulation of Glycolysis and Gluconeogenesis
What is the Cori cycle and why is it important?

57. Regulation of Glycolysis and Gluconeogenesis