1. 14| Glucose Utilization and Biosynthesis
© 2013 W. H. Freeman and Company

2. Chapter 14. Glycolysis, gluconeogenesis, and the pentose phosphate pathway
* Three fates of glucose in higher plants and animals

3. I. Glycolysis
Glucose + 2NAD+ + 2ADP + 2Pi  2pyruvate + 2NADH + 2H+ + 2ATP + 2H2O
① Preparatory phase
Glucose + 2ATP  2glyceraldehyde 3-phosphate + 2ADP
Raising the free-energy content of the intermediates by the phosphoryl group transfer from ATP
② Payoff phase
2glyceraldehyde 3-phosphate + 2NAD+ + 4ADP + 2Pi  2pyruvate + 2NADH + 2H+ + 4ATP + 2H2O

7. * Fates of pyruvate (in terms of catabolism)
Electrons (as forms of NADH and FADH2)  O2
respiratory electron transport chain

8. * Free-energy change of glycolysis
Glucose + 2NAD+  2pyruvate + 2NADH + 2H+ ΔG’°=-146 kJ/mol
2ADP + 2Pi  2ATP + 2H2O ΔG’°=61 kJ/mol
Sum ΔG’°=-85 kJ/mol
Glucose + 2NAD+ + 2ADP + 2Pi  2pyruvate + 2NADH + 2H+ + 2ATP + 2H2O
Glucose  (glycolysis) 2pyruvate (TCA cycle) 6CO2
ΔG’°=-146 kJ/mol
ΔG’°=-2840 kJ/mol

9. * 10 reactions in glycolysis
① phosphorylation of glucose
glucose + ATP  glucose 6-phosphate + ADP ΔG’°=-16.7 kJ/mol
Irreversible reaction under cellular conditions
Hexokinase
Phosphorylation of glucose, fructose, mannose
Induced fit
Mg2+ is required

10. ② Conversion of glucose 6-phosphate to fructose 6-phosphate
Glucose 6-phosphate ↔ fructose 6-phosphate ΔG’°=1.7 kJ/mol
Phosphohexose isomerase
Specific for glucose 6-phosphate, fructose 6-phosphate
Mg2+-dependent
참고) isomerase, mutase, epimerase

11. Isomerase: aldose <-- ketose

12. Epimerase

13. ③ Phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate
Irreversible reaction under cellular conditions
Phosphofructokinase-1
Mg2+-dependent
In plants
fructose 6-phosphate + PPi  fructose 1,6-phosphate + Pi ΔG’°=-14.0 kJ/mol

14. ④ Cleavage of fructose 1,6-bisphosphate
Fructose 1,6-bisphosphate aldolase

15. ⑤ Interconversion of the triose phosphates
dihydroxyacetone phosphate ↔ glyceraldehyde 3-phosphate ΔG’°=7.5 kJ/mol
Triose phosphate isomerase

17. ⑥ Oxidation of glyceraldehydes 3-phosphate to 1,3-bisphosphoglycerate
Glyceraldehyde 3-P dehydrogenase
-Cys residue at the active site (reactivity to iodoacetate)
-Phospholysis
-NAD as coenzyme
Hydrolysis of acyl phosphate: ΔG’°=-49.3 kJ/mol

19. ⑦ Phosphoryl transfer from 1,3-bisphosphoglycerate to ADP
Phosphoglycerate kinase: Mg2+-dependent
Substrate-level phosphorylation: the formation of ATP by phosphoryl group transfer from a substrate to ADP

20. ⑧ Conversion of 3-phosphoglycerate to 2-phosphoglycerate
Phosphoglycerate mutase
-Mg2+-dependent
-His residue at the active site
-3-phosphoglycerate  2,3-bisphosphoglycerate  2-phosphoglycerate
-Muatase: an enzyme that catalyze the transfer of a functional group from one position to another in the same molecule
[2,3-bisphosphoglycerate]↑  the affinity of Hb for O2↓ in erythrocytes

22. ⑨ Dehydration of 2-phosphoglycerate to PEP
ΔG’° of hydrolysis of the phosphate group
- 2-phosphoglycerate: kJ/mol
- PEP: kJ/mol
Enolase

23. ⑩ Transfer of the phosphoryl group from PEP to ADP
Irreversible reaction under intracellular conditions
Substrate-level phosphorylation
Pyruvate kinase: K+, Mg2+ (Mn2+)-dependent

24. * The overall balance sheet of glycolysis
In cytosol
Glucose + 2NAD+ + 2ADP + 2Pi  2pyruvate + 2NADH + 2H+ + 2ATP + 2H2O
In the presence of O2
2NADH + 2H+ + O2  2NAD+ + 2H2O (respiratory electron transport)
in the innermenbrane of mitochondria
in the PM of prokaryotes
↓ : respiration-linked phosphorylation
ATP

25. * The glycolysis rate is high in cancer cells
Glucose uptake and glycolysis proceed about ten times faster in most solid
Tumors than in noncancerous tissues

26. * Fates of pyruvate under aerobic and anaerobic conditions
1. under aerobic conditions
glycolysis
TCA cycle
Glucose Pyruvate acetyl-CoA CO2+4H2O
2NAD+
2NADH
2NAD+
2NADH
6NAD+
6NADH
2FADH2
2FAD
In the presence of O2
2NADH + 2H+ + O2  2NAD+ + 2H2O (respiratory electron transport)
in the innermenbrane of mitochondria
in the PM of prokaryotes
↓ : respiration-linked phosphorylation
ATP

27. 2. under anaerobic and hypoxic conditions
① lactic acid fermentation
in very active skeletal muscle and submerged plant parts
in lactobacillus, streptococcus
2NAD+
2NADH
Glucose

28. Lactobacillus, streptococcus
Lactose  lactic acid  lactate + H+  acidification of milk  denaturation of casein and other milk proteins  cheese, yogurt

29. ② Alcohol fermentation
in yeast
2NAD+
2NADH
Glucose

30. Pyruvate decarboxylase
-Mg2+-dependent
-Thiamine pyrophosphate (TPP) as a coenzyme (derived from Vitamin B1, beriberi)
-absent in vertebrate tissues and in other organisms that carry out lactic acid fermentation
-TPP
important role in the cleavage of bonds adjacent to a carbonyl group
(decarboxylation of a-keto acids, acyl group transfer)
The thiazolium ring of TPP: deprotonation of the C2 carbon  nucleophilic attack on the carbon atom of a carbonyl group

31. Electron sink로서의 역활

33. * Feeder pathways for glycolysis

34. 1. Glycogen and starch are degraded by phosphorolysis
Glycogen  glucose 1-P  glucose 6-P
Glycogen phosphorylase phosphoglucomutase
Srarch  glucose 1-P  glucose 6-P
Starch phosphorylase (in plants)

35. ① Glycogen (starch) phosphorylase
-cofactor: pyridoxal phosphate
-(a14) glucosidase activity
② Debranching enzyme
-transferase activity
-(a16) glucosidase activity
③ Phosphoglucomutase
-serine at the active site
-glucose 1-P  glucose 1,6-bisP
 glucose 6-P

36. Glycogenin (7-8 glucose)
Glycogen synthase
UDP-glucose

37. 참고1
Anomeric carbon
Anomer

38. 참고2
Anomeric carbon

39. 참고3
(a14) glycosidic bond
(a16) glycosidic bond

40. 2. Fructose
Fructose + ATP  fructose 6-P + ADP (in the muscle and kidney)
Hexokinase (Mg2+)

41. 2. Fructose
In the liver
Fructose + ATP  ADP + fructose 1-P  glyceraldehyde + DHA-P
Fructokinase (Mg2+) Fructose 1-P aldolase
Glyceraldehyde  glyceraldehyde 3-P (triose kinase)
DHA-P  gleceraldehyde 3-P (triose phosphate isomerase)
Glyceraldehyde
3-phosphte

42. 3. Galactose
galactose + ATP  glucose 1-P + ADP
↓ phosphoglucomutase
glucose 6-P

43. 4. Mannose
Mannose + ATP  ADP + mannose 6-P  fructose 6-P
Hexokinase (Mg2+) phosphomannose isomerase

44. 5. Polysaccharides and disaccharides
Starch (glycogen)  oligosaccharide  maltose + dextrin
a-amylase (in saliva) a-amylase secreted from pancreas into the small
intestine

45. Enzymes that hydrolyze disaccharides and dextrin are located
on the outer surface of the intestinal epithelial cells
Dextrin + nH2O  n glucose (dextrinase)
Maltose + H2O  2glucose (maltase)
Lactose + H2O  galactose + glucose (lactase)
Sucrose + H2O  fructose + glucose (sucrase)
Trehalose + H2O  2glucose (trehalase)
Monomers  epithelial cell  blood  various tissues
Lactose intolerance
Microvillus (villi)

46. Gluconeogenesis
2pyruvate + 4ATP + 2GTP + 2NADH + 4H2O
 glucose + 4ADP + 2GDP + 6Pi + 2NAD+ + 2H+
Gluconeogenesis occurs in all animals, plants, fungi, and microorganisms
In mammals, gluconeogenesis takes place mainly in liver and to a lesser extent in renal cortex
glucolysis
Glucose
2 pyruvate
gluconeogenesis

51. Conversion of pyruvate to PEP
Pyruvate+HCO3-+ATP 
Oxaloacetate+ADP+Pi
Oxaloacetate+NADH+H+<-> malate+NAD+
Oxaloacetate+GTPPEP+CO2+GDP
Biotin:
Carboxyl carrier
[NADH]/[NAD+]=8X10-4 in cytosol
Gluconeogenesis에 필요한 NADH 부족

52. Glucose 6-phosphatase is found in ER
The enzyme is present in liver, kidney (renal cortex), and epithelial cells of the small intestine but not in other tissues

53. * The pentose phosphate pathway of glucose oxidation
(phosphogluconate pathway)
1. Oxidative reactions of the pentose phosphate pathway
2. Non-oxidative reactions of the pentose phosphate pathway

54. 1. Oxidative reactions of the pentose phosphate pathway
Glucose 6-P + 2NADP+ + H2O 
ribose 5-P + CO2 + 2NADPH + 2H+
Ribose 5-P  a precursor for nucleotide
synthesis
NADPH  reductant for anabolisms

55. In tissues that require primarily NADPH rather than ribose 5-P
6 ribose 5-P  5 glucose 6-P
non-oxidative pentose phosphate pathway
Transketolase : 2-carbon transfer from ketose to aldose
Transaldolase : 3- carbon transfer from ketose to aldose
Aldose: glyceraldehyde 3-P (C3), erythrose 4-P (C4), ribose 5-P (C5),
glucose 6-P
Ketose: xylulose 5-P (C5), fructose 6-P (C6), sedoheptulose 7-P (C7)

58. * Regulation of glycolysis
Homeostasis of the ATP concentration
A  B  C  D  E : metabolic pathway
E1 E2 E3 E4
E1, E3, E4: activities are high
E2: activity is low  rate-limiting step
Rate-limiting step (BC)
-very exergonic reaction (ΔG << 0)
-irreversible reaction under cellular conditions
-the target of metabolic regulation
* Regulation points of glycolysis
① Hexokinase ② phosphofructokinase-1 ③ pyruvate kinase

59. 1. Regulation of phosphofructokinase-1 (PFK-1)
Fructose 6-P + ATP  fructose 1,6-bisP + ADP
Allosteric regulator (effector): ATP, ADP, AMP, citrate, fructose 2,6-bisP
-ATP, citrate: inhibition of PFK-1
-AMP, fructose 2,6 bisP: activation of PFK-1
Allosteric site
Active site
PFK-1 in plants is not regulated by fructose 2,6-bisP
PFK-1 in plants is inhibited by PEP

61. Glucagon (secreted from pancreas)  increase [glucose] in blood
Low [glucose] in blood
 secretion of glucagon from pancreas
 binding of glucagon to the receptor in the liver cell
 activation of AC
 increase in [cAMP]
 activation of PKA
 phosphorylation of PFK-2/FBPase-2
 increase in FBPase-2 activity
 decrease in [fructose 2,6-bisP]
 Low PFK-1 activity
 low glycolysis rate
Phosphofructokinase-2 (PFK-2)
Fructose 6-P
Fructose 2,6-bisP
Fructose bisphosphatase-2 (FBP-2)
PFK-2/FBP-2
Phosphorylated form : FBP-2 > PFK-2
Unphosphorylated form : PFK-2 > FBP-2

62. ② Regulation of hexokinase
Glucose + ATP  glucose 6-P and ADP
Isozymes: different proteins that catalyze the same reaction
Hexokinase II in myocytes: Km = 0.1 mM glucose
Inhibited by glucose 6-P
Hexokinase IV (glucokinase) in the liver cell: Km = 10 mM
Inhibited by fructose 6-P
③ Pyruvate kinase
PEP + ADP  pyruvate + ATP
Allosteric regulator: ATP, acetyl-CoA, fatty acid (all are inhibitors)
AMP, fructose 1,6-bisphosphate (activators)

63. Regulation of glycolysis and gluconeogenesis
2pyruvate + 4ATP + 2GTP + 2NADH + 4H2O
 glucose + 4ADP + 2GDP + 6Pi + 2NAD+ + 2H+
Gluconeogenesis occurs primarily in the liver
glucolysis
Glucose
2 pyruvate
gluconeogenesis
Futile cycling

64. Three irreversible reactions in glycolysis
Hexokinase  glucose 6-phosphatase
PFK  FBP-1
Pyruvate kinase  pyruvate carboxylase
malate DH
PEP carboxykinase

65. Regulation
Fructose 2,6 bisP : activation of PFK-1, inhibition of FBP-1
High [ATP]  glycolysis억제, gluconeogenesis선호