Carbohydrate metabolism

These are major source of energy for living organisms.
Supplying a huge array of metabolic intermediates for biosynthetic reactions.
The structural elements in cell coat or connective tissues.

1. Carbohydrate Metabolism
Mr.Tapeshwar Yadav.
II year M.Sc. Biochemistry
Mamata Medical College
Khammam

2. Carbohydrates
Definition : Carbohydrates are
polyhydroxy aldehydes or ketones.

3. Biological significance of
Carbohydrates
•These are major source of energy for
living organisms.
•Supplying a huge array of metabolic
intermediates for biosynthetic
reactions.
•The structural elements in cell coat
or connective tissues.

4. Digestion :
•Partly digested in mouth by salivary
amylase.
•In stomach there is no digestion takes
place.
•Complete digestion and absorption
will be taken place at small intestine

5. Glucose transporters (GLUT)
•There are 5 types GLUT
–GLUT1: RBC
–GLUT4: Adipose tissue, Muscle

6. The metabolism of glucose
•Aerobic oxidation
•Glycolysis
•Gluconeogenesis
•Pentose phosphate pathway
•Glycogenesis
•Glycogenolysis
•Uronic acid pathway

7. Glycogen
Glycogenesis Glycogenolysis
Pentose phosphate
pathway
Ribose, NADPH
GlycolysisPyruvate/
Lactate
H
2
O+CO
2
A
e
r
o
b
ic

o
x
id
a
tio
n
D
ig
e
s
tio
n

a
b
s
o
r
p
t
io
n
Starch
Lactate,
Amino
acids,
Glycerol
Glucose
G
luconeo
-genesis

8. Aerobic oxidation
•C
6
H
12
O
6
6H
2
O+6CO
2
+ Energy
(in the form of heat)

11. Glycolysis

12. •The anaerobic catabolic pathway by
which a molecule of glucose is
broken down into two molecules of
lactate.
Glucose → 2 Lactic acid (lack of O
2
)
•All of the enzymes of glycolysis
locate in cytosol.

13. Glycolysis overview
Glucose
Pyruvate
Lactic acid
Glycolysis
If O
2
is not available

14. 1) Glycolytic pathway :
Glucose → Pyruvate
including 10 reactions.

15. •Phosphorylated Glucose cannot get
out from cell.
•Hexokinase (having 4 Isoenzymes).
•Glucokinase, GK in liver.
•Irreversible.
(1) Glucose is phosphorylated to
Glucose 6-phosphate
OH
OH
H
OH
H
OHH
OH
CH
2
H
HO
OH
OH
H
OH
H
OHH
OH
CH
2
H
OP
ATP ADP
Hexokinase
Mg
2+
G G-6-P

16. Particulars Hexokinase Glucokinase
Occurrence in all tissues only in liver
K
m
value 0.1mmol/L 10mmol/L
Substrate Glucose,
Fructose,
Mannose
Glucose
Regulation G-6-P Insulin
Comparison of
Hexokinase and Glucokinase

17. (2) G-6-P is isomerised to Fructose 6-P
OH
OH
H
OH
H
OHH
OH
CH
2
H
OP
G-6-P
isomerase OH
CH
2OH
H
CH
2
OHH
H
OH
O
OP
F-6-P

18. (3) F-6-P is phosphorylated Fructose
1,6-bisphosphate
•The second phosphorylation
•Phosphofructokinase-1, PFK-1
OH
CH
2OH
H
CH
2
OHH
H OH
O
OP
F-1,6-BP
OH
CH
2
H
CH
2
OHH
H
OH
O
OP OP
ATP ADP
Mg
2+
F-6-P
PFK-1

19. (4) F-1,6-BP cleaved to 2 Triose
phosphates
•Reversible
F-1,6-BP
CH
2
CO
CHHO
COHH
COHH
CH
2
OP
OP
CH
2
CO
OP
CHO
CHOH
CH
2OPCH
2OH
+
aldolase
dihydroxyacetone
phosphate,
DHAP
glyceraldehyde
3-phosphate,
GAP

20. (5) Triose phosphate isomerization
G→2 molecule glyceraldehyde-3-
phosphate, consume 2 ATP .
CH
2
CO
OP
CHO
CHOH
CH
2OPCH
2OH
DHAP GAP
phosphotriose
isomerase

21. (6) Glyceraldehyde 3-phosphate oxidised
1,3-bisphospho glycerate
CHO
CHOH
CH
2OP
NAD
+
NADH+H
+
Pi
glyceraldehyde
3-phosphate
dehydrogenase,
GAPDH
C
CHOH
CH
2OP
O O~P
glycerate
1,3-bisphosphate,
1,3-BPG
glyceraldehyde
3-phosphate

22. (7) 1,3-BPG dephosphorylated to 3-
phospho glycerate
•Substrate level phosphorylation
COO
-
CHOH
CH
2OP
C
CHOH
CH
2OP
O O~P
ADP ATP
glycerate
1,3-bisphosphate
glycerate
3-phosphate
Phosphoglycerate
kinase

23. (8) Glycerate 3-phosphate mutated
glycerate 2-phosphate
COO
-
CHOH
CH
2OP
COO
-
CH
CH
2OH
OP
glycerate
3-phosphate
glycerate
2-phosphate
Mutase

24. (9) Glycerate 2-phosphate →
phosphoenol pyruvate
COO
-
CH
CH
2OH
OP
COO
-
C
CH
2
O
PEP
~P+ H
2O
enolase
glycerate
2-phosphate

25. (10) PEP →pyruvate
•Second substrate level
phosphorylation
•irreversible
COO
-
C
CH
3
ADP ATP
COO
-
C
CH
2
O
PEP
~P
pyruvate kinase
O
Pyruvate

26. 2) Pyruvate → lactate
COO
C
CH
3
NAD
+
NADH + H
+
O
Pyr
COO
CHOH
CH
3
Lactate dehydrogenase,
LDH
Lactic acid

27. Summary of Glycolysis
ATP
ADP
Mg
2+
PFK-1
GAP DHAP
glycerate
1,3-bisphosphate
NADH+H
+
glyceraldehyde
3-phosphate
dehydrogenase
H
3PO
4
NADH+H
+
NAD
+
ADP
ATP
glycerate
3-phosphate
glycerate
2-phosphate
H
2O
PEP
ATP
ADP
pyruvate kinase
lactate
pyruvate
G G-6-P F- 6-P F- 1,6-BP
NAD
+
Phosphoglycerate
kinase
Isomerase
Aldolase
Mutase
Enolase
LDH
HK
ATP
ADP
Mg
2+

28. Total reaction:
C
6
H
12
O
6
+ 2ADP + 2Pi
2CH
3
CHOHCOOH + 2ATP + 2H
2
O
Formation of ATP:
The net yield is 2 ~P or 2 molecules of
ATP per glucose.

29. 2. Regulation of Glycolysis
•Three key enzymes catalyze
irreversible reactions : Hexokinase,
Phosphofructokinase & Pyruvate
Kinase.

30. 1) PFK-1
The reaction catalyzed by PFK-1 is
usually the rate-limiting step of the
Glycolysis pathway.
This enzyme is regulated by covalent
modification, allosteric regulation.

31. bifunctional
enzyme

32. 2) Pyruvate kinase
•Allosteric regulation:
F-1,6-BP acts as allosteric activator；

ATP and Ala in liver act as allosteric
inhibitors;

33. • Covalent modification:
phosphorylated by Glucagon
through cAMP and PKA and inhibited.
ATP ADP
PKA
Glucagon
Pyruvate Kinase
(active)
Pyruvate Kinase- P
(inactive)
cAMP

34. 3) Hexokinase and glucokinase
•This enzyme is regulated by covalent
modification, allosteric regulation and
isoenzyme regulation.
•Inhibited by its product G-6-P.
•Insulin induces synthesis of
glucokinase.

35. 3. Significance of glycolysis
1) Glycolysis is the emergency energy-
yielding pathway.
2) Glycolysis is the main way to
produce ATP in some tissues, even
though the oxygen supply is
sufficient, such as red blood cells,
retina, testis, skin, medulla of kidney.
•In glycolysis, 1mol G produces 2mol
lactic acid and 2mol ATP.

36. § 3 Aerobic Oxidation of
Glucose

37. •The process of complete
oxidation of glucose to CO
2
and
water with liberation of energy as
the form of ATP is named aerobic
oxidation.
•The main pathway of G oxidation.

38. 1. Process of aerobic oxidation
G Pyr
cytosol Mitochodria
glycolytic
pathway
second
stage
third
stage
CO
2+ H
2O+ATP
Pyr CH
3CO~SCoA
first
stage
TAC

39. 1) Oxidative decarboxylation of
Pyruvate to Acetyl CoA
•irreversible;
•in mitochodria.
COO
-
C
CH
3
NAD
+
NADH + H
+
O
pyruvate
CH
3C
Pyruvate
dehydrogenase
complex
Acetyl CoA
O
~SCoA+ HSCoA + CO
2

40. Pyruvate dehydrogenase complex:
E
1
pyruvate dehydrogenase
Es E
2
dihydrolipoyl transacetylase
E
3
dihydrolipoyl dehydrogenase
thiamine pyrophosphate, TPP (VB
1
)
HSCoA (pantothenic acid)
cofactors lipoic Acid
NAD
+
(Vpp)
FAD (VB
2
)

41. HSCoA
NAD
+
Pyruvate dehydrogenase complex:

42. The structure of
pyruvate dehydrogenase complex

43. SS
CH
H
2
C
H
2C (CH
2)
4COOH
SH SH
CH
H
2
C
H
2C (CH
2)
4COOH
+2H
-2H
lipoic acid dihydrolipoic acid
C
C
NH
2
HC
N
C
H
2
S
C
C
N
C
N
C
H
CH
3
CH
2CH
2H
3C OPO
O
-
O
P
O
O
-
O
-
+
TPP

44. HSCoA
HSCH
2CH
2NHCCH
2
O
CH
2NHCC
O
OH
H
CCH
2
CH
3
CH
3
OPO
OH
O
P
OH
O
O
3'AMP
¦Â-alaninepantoic acidpyrophosphate
pantothenic acid
4'-phosphopantotheine
¦Â-mercapto-
ethylamine

45. CO
2
CoASH
NAD
+
NADH
+H
+

46. 2) Tricarboxylic acid cycle, TCAC
•The cycle comprises the combination of a
molecule of acetyl-CoA with oxaloacetate,
resulting in the formation of a six-carbon
tricarboxylic acid, citrate. There follows a
series of reactions in the course of which
two molecules of CO
2
are released and
oxaloacetate is regenerated.
•Also called citrate cycle or Krebs cycle.

47. (1) Process of reactions

51. Citrate cycle
CO
CH
2
COO
COO
CH
3CO~SCoA
C
CH
2
COO
COO
CH
2
HO
COO
C
CH
COO
COO
CH
2COO
CH
CH
COO
COO
CH
2COO
H
2O
H
2O
HO
CO
2
CH
2
CH
2
COCOO
COOCH
2
CH
2
COO
CO~SCoA CO
2
NAD
+NADH+H
+
CH
2
CH
2
COO
COO
GDP+PiGTP
CH
CH
2
COO
COO
OOCCH
CCOOH
HO
NAD
+
NADH+H
+
FAD
FADH
2
H
2O
acetyl CoA
H
2O
oxaloacetate
citrate
synthase
citrate
aconitase
cis-aconitate
aconitase
isocitrate
NAD
+
NADH+H
+
isocitrate dehydrogenase
¦Á-keto-
glutarate
¦Á-ketoglutarate
dehydrogenase
complex
succinyl-CoA
ADPATP
CoASH
succinyl CoA
syntetase
succinate dehydrogenase
fumarate
succinate
fumarase
malate
malate dehydrogenase
HSCoA
HSCoA

52. Summary of
Krebs Cycle
①
Reducing
equivalents

53. ② The net reaction of the TCAC:
acetylCoA+3NAD
+
+FAD+GDP+Pi+2H
2
O
→2CO
2
+3NADH+3H
+
+FADH
2
+GTP+
HSCoA
③ Irreversible and aerobic reaction
④ The enzymes are located in the
mitochondrial matrix.

54. ⑤
Anaplerotic reaction of
oxaloacetate
pyruvate carboxylase
Biotin
ATP ADP + Pi
+ CO
2C
CH
3
COOH
O
C
C
COOH
COOH
O
H
2
NAD
+
NADH+H
+
malic acid DH
+ CO
2
malic enzyme
C
CH
3
COOH
O
NADPH+H
+
NADP
+
CHOH
C
COOH
COOH
C
C
COOH
COOH
O
H
2H
2

55. (2) Bio-significance of TCAC
① Acts as the final common pathway for
the oxidation of carbohydrates, lipids,
and proteins.
② Serves as the crossroad for the
interconversion among carbohydrates,
lipids, and non-essential amino acids,
and as a source of biosynthetic
intermediates.

56. Krebs Cycle is at the
hinge of metabolism.

57. 2. ATP produced in the aerobic
oxidation
•acetyl CoA → TCAC : 3 (NADH+H
+
) +
FADH
2
+ 1GTP → 12 ATP.
•pyruvate →acetyl CoA: NADH+H
+
→

3 ATP
•1 G → 2 pyruvate : 2(NADH+H
+
) → 6 or
8ATP
1mol G： 36 or 38mol ATP
（12＋3 ）×2 ＋ 6（ 8 ）＝
36（ 38 ）

58. 3. The regulation of aerobic
oxidation
•The Key Enzymes of aerobic oxidation
The Key Enzymes of glycolysis
Pyruvate Dehydrogenase Complex
Citrate synthase
Isocitrate dehydrogenase (rate-limiting )
a-Ketoglutarate dehydrogenase

59. (1) Pyruvate dehydrogenase complex
Pyruvate dehydrogenase
(active form)
allosteric inhibitors:
ATP, acetyl CoA,
NADH, FA
allosteric activators:
AMP, CoA,
NAD
+
,Ca
2+
pyruvate dehydrogenase
(inactive form)
P
pyruvate dehydrogenase
kinase
pyruvate dehydrogenase
phosphatase
ATP
ADP
H
2O
Pi
Ca
2+
,insulin
acetyl CoA,
NADH
ADP,
NAD
+

60. (2) Citrate synthase
•Allosteric activator: ADP
•Allosteric inhibitor: NADH, succinyl CoA,
citrate, ATP
(3) Isocitrate dehydrogenase
•Allosteric activator: ADP, Ca
2+
•Allosteric inhibitor: ATP
(4) a-Ketoglutarate dehydrogenase
•Similar with Pyruvate dehydrogenase complex

62. Oxidative
phosphorylation→TCAC↑
•ATP/ADP↑ inhibit TCAC,
Oxidative phosphorylation ↓
•ATP/ADP↓，promote
TCAC，
Oxidative phosphorylation ↑

63. 4. Pasteur Effect
•Under aerobic conditions, glycolysis is
inhibited and this inhibitory effect of
oxygen on glycolysis is known as
Pasteur effect.
•The key point is NADH ：
NADH mitochondria
Pyr TCAC CO
2＋H
2O
Pyr can’t produce to lactate.

64. §4 Pentose Phosphate
Pathway

65. 1. The procedure of pentose
phosphate pathway/shunt
 In cytosol

66. 1) Oxidative Phase
NADP
+
NADPH+H
+
H
2O
CO
2
G-6-P
Xylulose 5-P
Ribulose 5-P
Ribose 5-P
G-6-P
dehydrogenase
6-Phosphogluconate
6-phosphogluconate
dehydrogenase
6-Phospho
gluconolactonase
6-phosphogluco-
nolactone
Epimerase
Isomerase
NADP
+
NADPH+H
+

67. 2) Non-Oxidative Phase
Ribose 5-p
Xylulose 5-p
Xylulose 5-p
Fructose 6-p
Glyceraldehyde 3-p
Fructose 6-p
• Transketolase: requires TPP
• Transaldolase
Glycolysis

68. The net reation:
3G-6-P + 6NADP
+
→
2F-6-P + GAP + 6NADPH + H
+
+ 3CO
2
2. Regulation of pentose phosphate
pathway
Glucose-6-phosphate Dehydrogenase is the
rate-limiting enzyme.
NADPH/NADP
+
↑, inhibit;
NADPH/NADP
+
↓, activate.

69. 3. Significance of pentose
Phosphate pathway
1) To supply ribose 5-phosphate for bio-
synthesis of nucleic acid;
2) To supply NADPH as H-donor in
metabolism;
 NADPH is very important “reducing
power” for the synthesis of fatty acids
and cholesterol, and amino acids, etc.

70.  NADPH is the coenzyme of glutathione
reductase to keep the normal level of
reduced glutathione;
So, NADPH, glutathione and glutathione
reductase together will preserved the integrity
of RBC membrane.
2GSH
G-S-S-G NADPH + H
+
glutathione reductase
NADP
+
H
2O
2
2H
2O

71. Deficiency of glucose 6-phosphate
dehydrogenase results in hemolytic
anemia.
favism
 NADPH serves as the coenzyme of
mixed function oxidases (mono-
oxygenases). In liver this enzyme
participates in biotransformation.

72. §5 Glycogen synthesis and
catabolism

73. Glycogen is a polymer of glucose
residues linked by
a (1→4) glycosidic bonds, mainly
a (1→6) glycosidic bonds, at
branch points.

75. • The process of glycogenesis
occurs in cytosol of liver and
skeletal muscle mainly.
1. Glycogen synthesis (Glycogenesis)

76. •UDPG: G active pattern, G active donor.
•In glycogen anabolism, 1 G consumes
2~P.
•Glycogen synthase: key E.
G
HK or GK
G-6-P
ATP ADP
G-1-P
UDPG
pyrophosphorylase
UDPG
UTP PPi Gn UDP
Gn+1
glycogen
synthase

77. O
O
OHOH
HH
H
CH
2
H
HN
N
O
O
OP
O
O
-
P
O
O
-
H
O
OH
H
OHH
OH
CH
2OH
H
O
H
UDPG

79. Branching enzyme

80. Phosphorylase: key E;
The end products: 85% of G-1-P and 15%
of free G;
There is no the activity of glucose 6-
phosphatase (G-6-Pase) in skeletal
muscle.
Gn
Pi Gn-1
G-1-P G-6-P
G-6-Pase
H
2O Pi
G
Phosphorylase
2. Glycogen catabolism (glycogenolysis)

81. Debranching enzyme:

glucan transferase
a-1,6-glucosidase

82. Nonreducing ends
(a1→6) linkage
Glycogen
phosphorylase
(a1→6) glucosidase activity of
debranching enzyme
Glucose
Transferase activity of
debranching enzyme

83. 3. Regulation of glycogenesis and
glycogenolysis
1) Allosteric regulation
In liver:
G phosphorylase
glycogenolysis
In muscle:
AMP
phosphorylase-b
ATP
G-6-P
phosphorylase-a
glycogenolysis
Ca
2+

84. 2) Covalent modification
Glucagon
epinephrine
Adenylyl
cyclase
cAMP
G proteinreceptor
PKA
glycogenolysis
Phosphorylase
Glycogen synthase
glycogenesis
Blood sugar

85. glucagon, epinephrine
inactive
adenylate cyclase
active
adenylate cyclase
ATP cAMP
inactive
PKA

active
PKA
phosphorylase b
kinase
phosphorylase b
kinase
P
ATP
ADP
H
2O
Pi
phosphorylase b
P
P
ATP ADP
Pi
H
2O
ATP ADP
glycogen
synthase
glycogen
synthase
P
H
2OPi
protein
phosphatase-1
(active) (inactive)
inhibitor-1
(active)
inhibitor-1
(inactive)
phosphorylase a
ATP

86. §6 Gluconeogenesis

87. •Concept:
The process of transformation of non-
carbohydrates to glucose or glycogen
is termed as gluconeogenesis.
•Materials: lactate, glycerol, pyruvate
and glucogenic amino acid.
•Site: mainly liver, kidney.

88. 1. Gluconeogenic pathway
•The main pathway for gluconeogenesis
is essentially a reversal of glycolysis,
but there are three energy barriers
obstructing a simple reversal of
glycolysis.

89. 1) The shunt of carboxylation of Pyr
PEP
ADP
ATP
oxaloacetic acid
Pyr carboxylase
ADP+Pi ATP CO
2
Biotin
GTP
GDP
CO
2
PEP carboxykinase
Pyr kinase
COO
-
C
CH
3
COO
-
CH
CH
2
O~P
O
pyruvate
COO
-
C
CH
2
O
COOH £¨Mt.£©
£¨1/3Mt. 2/3cytosal£©.

90. 2) F-1, 6-BP →F-6-P
F-6-P F-1,6-BP
ATP ADP
Pi H
2O
PFK-1
Fructose-
bisphosphatase

91. 3) G-6-P →G
•2 lactic acid G consume
ATP?
G G-6-P
ATP ADP
Pi H
2O
Glucose-6-
phosphatase
HK

92. gluconeogenesis
glucose
G-6-P
glycogen
F-1,6BP
glyceral-
dehyde 3-P
glycerol
1.3-bisphospho-
glycerate
glycerate 3-P
glycerate 2-P
lactate
G-1-P
malic acid
phosphoenol
pyruvate
pyruvate
GTP
GDP
CO
2
2/3
malic acid
pyruvate
phosphoenol
pyruvate
GTP
GDP
CO
2
1/3
CO
2
CYTOSOL MITOCHONDRIA
NAD
+
NADH+H
+
NAD
+
NADH+H
+
NAD
+
NADH+H
+
glutamate
¦Á-ketoglutarate¦Á-ketoglutarate
glutamate
OAAAspAspOAA
DHAP
ATP
ADP
ATP
ADP
PK
ADP
ATP
F-6-P

93. 2. Regulation of gluconeogenesis
•Substrate cycle:
The interconversion of two substrates
catalyzed by different enzymes for
singly direction reactions is called
“substrate cycle”.
•The substrate cycle produces net
hydrolysis of ATP or GTP.------futile
cycle

94. Key enzymes of gluconeogenesis

PEP carboxykinase
Pyr carboxylase
Fructose-bisphosphatase
Glucose-6-phosphatase

95. F-1,6-BP
ATP
ADP
Pi
H
2O
PFK-1
FBPase-1
F-6-P
F-2,6-BP
AMP
glycolysis
gluconeogenesis:

96. F-1,6-BP
ATP
ADP
F-2,6-BP
PEP
Pyr
acetyl CoA
glucagon
insulin
glucagon
Ala in liver
OAA

97. 3. Significance of gluconeogenesis
(1)Replenishment of Glucose by
Gluconeogenesis and Maintaining
Normal Blood Sugar Level.
(2)Replenishment of Liver Glycogen.
(3)Regulation of Acid-base Balance.

98. First stages
(cytosol)
Second stages
(Mt.)
Third stages
(Mt.)

99. Lactic acid (Cori) cycle
•Lactate, formed by the oxidation of
glucose in skeletal muscle and by
blood, is transported to the liver where
it re-forms glucose, which again
becomes available via the circulation
for oxidation in the tissues. This
process is known as the lactic acid
cycle or Cori cycle.
•prevent acidosis；reused lactate

100. muscle
glucose
pyruvate
lactate
glucose
blood
pyruvate
lactate
glycolytic
pathway
glucose
liver
lactate
NAD
+
NADH+H
+
NADH+H
+
NAD
+
gluconeo-
genesis
Lactic acid cycle

101. §6 Blood Sugar and Its
Regulation

102. 1. The source and fate of blood sugar
blood sugar
3.89¡«6.11mmol/L
dietary supply
liver glycogen
(gluconeogenesis)
other saccharides
CO
2 + H
2O + energy
glycogen
other saccharides
non-carbohydrates
>8.89¡«10.00mmol/L
(threshold of kidney)
non-carbohydrate
(lipids and some
amino acids)
urine glucose
origin (income) fate (outcome)

103. Blood sugar level must be maintained
within a limited range to ensure the
supply of glucose to brain.
The blood glucose concentration is 3.89
～6.11mmol/L normally.

104. 2. Regulation of blood sugar level
1）insulin： for decreasing blood sugar
levels.
2）glucagon：for increasing blood sugar
levels.
3）glucocorticoid: for increasing blood
sugar levels.
4）adrenaline：for increasing blood
sugar levels.

105. 3. Abnormal Blood Sugar Level
•Hyperglycemia: > 7.22～7.78 mmol/L
•The renal threshold for glucose: 8.89
～10.00mmol/L
•Hypoglycemia: < 3.33～3.89mmol/L

106. Pyruvate as a junction point