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Carbohydrates
Dr. Omeed Akbar Ali
P h D . C l i n i c a l B i o c h e m i s t r y
T i k r i t U n i v e r s i t y - C o l l e g e o f M e d i c i n e
1
Carbohydrates
2
Carbohydrate is a biomolecule consisting of carbon (C), hydrogen (H) and
oxygen (O) atoms with general formula of Cm(H2O)n
CH2O
(CH2O)x C6H12O6
Carbohydrates Biosynthesis
Carbohydrates are predominantly biosynthesized by plants through photosynthesis.
Glucose is synthesized in plants from CO2, H2O, and solar energy from the sun.
chlorophyll
CO2 + H2O CH2O + O2
Sunlight aldehyde
3
Functional groups determine function
carbonyl
aldehyde
chlorophyll
CO2 + H2O CH2O + O2
Sunlight aldehyde
4
Functional groups determine function
carbonyl
ketone
Sugar structure
 Most names for sugars end in -ose
 Classified by number of carbons
 6C = hexose (glucose)
 5C = pentose (ribose)
 3C = triose (glyceraldehyde)
6
Types of Carbohydrates
Classification based on the number of sugar units in
the total chain
 Monosaccharides
 Disaccharides
 Oligosaccharides
 Polysaccharides
Types of Carbohydrates
 Monosaccharides
 Single sugar unit :
 Glucose
 Fructose
 Disaccharides
 2 monomers sugars :
 Maltose
 Sucrose
 Lactose
7
α-(1,4)
Isomaltose?
α-(1,6)
8
Building sugars
 Dehydration synthesis
|
fructose
|
glucose
monosaccharides
|
sucrose
(table sugar)
disaccharide
Lactose ?
H2O
αβ-(1,2)
β-(1,4)
Types of Carbohydrates
 Oligosaccharides
 up to 3-12 sugar units:
- Maltotriose
9
 Polysaccharides
• Large polymers
 > 13 sugar units:
 Homo-polysaccharides are polysaccharides composed of a single type of sugar monomer. For
example, Starch, Cellulose and Glycogen.
 Hetero-polysaccharides are polysaccharides that contain multiple monosaccharide units. Many
naturally occurring heteropolysaccharides have peptides, proteins, and lipids attached to them.
Some heteropolysaccharides examples are: Peptidoglycans, Agarose and Glycosaminoglycans.
Polysaccharides
10
 Polymers of sugars
 costs little energy to build
 easily reversible = release energy
 Function:
 energy storage
 starch (plants)
 glycogen (animals)
 in liver & muscles
Functions of Carbohydrates
 Source of energy for living beings, e.g. glucose.
 Storage form of energy, e.g. glycogen in animal tissue and starch in plants.
 Serve as structural component, e.g. glycosaminoglycans in humans, cellulose in
plants and chitin in insects.
 Non-digestable carbohydrates like cellulose, serve as dietary fibers.
 Constituent of nucleic acids RNA and DNA, e.g. ribose and deoxyribose sugar.
 Play a role in lubrication, cellular intercommunication and immunity.
 Carbohydrates are also involved in detoxification, e.g. glucuronic acid.
11
12
 Thus Carbohydrates are chief
constituents of human food.
 R.D.A for Dietary Carbohydrates=
400-600 gm/day.
Digestion, Absorption And Transport Of Carbohydrates
• The principal sites of carbohydrate digestion are the mouth and small intestine.
• Digestion in Mouth: Salivary glands secrete α-amylase (ptylin), which initiates the
hydrolysis of a starch. breaking some α-(1 → 4) bonds, α- amylase hydrolyzes starch
into dextrins.
• Digestion in Intestine: There are two phases of intestinal digestion.
1. Digestion due to pancreatic α-amylase
2. Digestion due to intestinal enzymes : sucrase, maltase, lactase, isomaltase.
13
14
α-Amylase
 Maltose
 Sucrose
 Lactose
Absorption And Transport Of Carbohydrates
Carbohydrates are absorbed as monosaccharides from the intestinal lumen.
• Two mechanisms are responsible for the absorption of monosaccharides:
1. Active transport against a concentration gradient, i.e. from a low glucose
concentration to a higher concentration.
2. Facilitative transport, with concentration gradient, i.e. from a higher
concentration to a lower one.
15
ADP+Pi
ATP
Glucose
Na+
K+
Na+
PUMP
Mucosal cells
of Intestinal
Lumen Portal
Na+-dependent glucose transporter, SGLT
Brush
border
cellular inner
membrane
Absorption mechanism
Fructose
Galactse
Glucose
GLUT-5
SGLT-1
Introduction to Metabolism
17
Metabolism: The sum of the chemical changes that convert nutrients into energy and
the chemically complex products of cells Hundreds of enzyme reactions organized
into discrete pathways.
• Substrates are transformed to products via many specific
intermediates Metabolic maps portray the reactions.
• Metabolism consists of catabolism and anabolism
Introduction to Metabolism
Catabolism: degradative pathways
 Usually energy-yielding!
 “destructive metabolism”
 FUELS -> -> CO 2 + H 2 O + useful energy.
Anabolism: biosynthetic pathways
 Energy-requiring!
 “Constructive metabolism”
 Useful energy + small molecules --> complex molecules.
18
Metabolism of Carbohydrates
19
Carbohydrate metabolism is a fundamental biochemical process that ensures a
constant supply of energy to living cells.
The most important carbohydrate is glucose, which can be broken down via
glycolysis, enter into the Kreb's cycle and oxidative phosphorylation to generate
ATP.
Metabolic pathways
 Glucose Metabolism
 Glycolysis
 Glycogenesis
 Glycogenolysis
 Gluconeogenesis
 Pentose phosphate pathway
 Fructose metabolism
 Galactose metabolism
20
目录
Part I
Glycolysis
Glycolysis
22
 Glycolysis: A process in which glucose is partially broken
down to two molecules of pyruvate (it is converted into lactate
finally ) by cells in enzyme reactions that do not need oxygen.
Glycolysis is also called anaerobic oxidation.
Position of glycolysis:cytoplasm
23
 Phase I------ glycolytic pathway: The six-carbon glucose break down
into two molecules of the three-carbon pyruvate.
 Phase II: Pyruvate is converted to lactate or Acetyl-CoA.
1. Glycolysis Has Two Phases:
Glycolysis
(Cytoplasm)
Acetyl-CoA
(Mitochondria)
24
25
1. Phosphorylation of Glucose
26
2. Conversion of G-6-P
to Fructose 6-Phosphate
27
3. Phosphorylation of F-6-P
to F-1,6-Bisphosphate
 6-phosphofructokinase-1
28
3. Phosphorylation of F-6-P
to F-1,6-Bisphosphate
 6-phosphofructokinase-1
4. Cleavage of Fructose 1,6-Bisphosphate
+
 Aldolase Enzyme
5. Interconversion of the Triose
Phosphates
6. Oxidation of Glyceraldehyde 3-
Phosphate to 1,3-Bisphosphoglycerate
7. Phosphoryl Transfer from 1,3
Bisphosphoglycerate to ADP
The formation of ATP by
phosphoryl group transfer
from a substrate such as
1,3-bisphosphoglycerate is
referred to as a substrate-
level phosphorylation
8. Conversion of 3-Phosphoglycerate to
2-Phosphoglycerate
9. Dehydration of 2-Phosphoglycerate to
Phosphoenolpyruvate
ADP ATP
K+ Mg2+
pyruvate kinase
10. Transfer of the Phosphoryl Group
from Phosphoenolpyruvate to ADP
Phosphoenolpyruvate
COOH
C
CH2
P
P
O
Pyruvate
COOH
C=O
CH3
36
 Position of glycolysis:cytoplasm
 Glycolysis is an anaerobic process through which ATP is synthesized .
 There are three irreversible steps in the process.
G G-6-P
ATP ADP
Hexokinase
ATP ADP
F-6-P F-1,6-2P
PFK-1
ADP ATP
PEP Pyruvate
Pyruvate kinase
Summary of glycolysis
Key
Enzymes
① Hexokinase
② Phosphofructokinase-1
③ Phosphoglycerate kinase
2. Regulation of Glycolysis: 3 key
enzymes
ADP ATP
F-1,6-P 3- P Glycerate
PGK
④ Pyruvate kinase
38
38
Phase II: Pyruvate is converted to lactate or Acetyl-CoA .
Pyruva
te
COOH
C=O
CH3
Lacta
te
COOH
CHOH
CH3
NADH + H+
NAD+
Acetyl-CoA
NADH+H+
CO2
TAC
Citrate
Co2 + NADH + H+
CoA-SH + NAD+
39
OVERVIEW
 Acetyl coA, the precursor for fatty acid
synthesis is produced from pyruvate,
ketogenic amino acids, fatty acid
oxidation and by alcohol metabolism.
 It is a substrate for TCA cycle and a
precursor for Oxidation , ketone bodies
and faty acids.
目录
Aerobic Oxidation
of Carbohydrate
Definition of Tri-carboxylic Acid Cycle
 The citric acid cycle is a series of reactions that brings about catabolism
of acetyl-coA liberating reducing equivalents which upon oxidation through
respiratory chain of mitochondria, generate ATP.
 It plays a central role in the breakdown or catabolism of organic fuel molecules—i.e
glucose and some other sugars, fatty acids, and some amino acids. Before these rather
large molecules can enter the TCA cycle they must be degraded into a two-carbon
compound called acetyl coenzyme A (acetyl CoA). Once fed into the TCA cycle, acetyl
CoA is converted into carbon dioxide and energy.
41
CoASH
NADH+H+
NAD+
CO2
NAD+
NADH+H+
CO2
GTP
GDP+Pi
FAD
FADH2
NADH+H+
NAD+
H2O
H2O
H2O
CoA-SH
CoA-SH
⑧
①
②
③
④
⑤
⑥
⑦
②
H2O
① Citrate Synthase
② Aconitase
③ Isocitrate Dehydrogenase
④ α-ketoglutarate dehydrogenase complex
⑤ Succinyl-CoA Synthetase
⑥ Succinate Dehydrogenase
⑦ Fumarase
⑧ Malate Dehydrogenase
GTP GDP
ATP
ADP
Nucleoside Diphosphate Kinase
1. The condensation of acetyl-CoA
with oxaloacetate to form
citrate.
2. Formation of Isocitrate via cis-
Aconitate.
3. Oxidation of Isocitrate to α-
Ketoglutarate and CO2.
4. Oxidation of α-Ketoglutarate to
Succinyl-CoA and
CO2.
5. Conversion of Succinyl-CoA to
Succinate.
6. Oxidation of Succinate to Fumarate.
7. Hydration of Fumarate to Malate.
8. Oxidation of Malate to
Oxaloacetate
 1. The Citric Acid Cycle Has Eight Steps
Energetics : 2 Acetyl CoA from 2 Pyruvate
 1NADH+H+ = 3/2.5 ATP
 1FADH2 = 2/1.5 ATP
 1GTP = 1 ATP
Acetyl-CoA + 3 NAD+ + [FAD] + GDP + Pi + 2 H2O CoA-SH
+ 3 NADH+3 H + +[FADH2] + GTP + 2 CO2
12 ×2=24
Indicator molecules of higher energy
state i.e. ATP, NADH, citrate, Acetyl
CoA – inhibit TCA cycle
Indicator molecules of low energy
state i.e. ADP, AMP, NAD+ – stimulate
TCA cycle
*
*
*
*
 Citrate synthase- There is allosteric inhibition of citrate synthase by ATP and long-chain
fatty acyl-CoA.
 Isocitrate dehydrogenase- is allosterically stimulated by ADP, which enhances the
enzyme's affinity for substrates. In contrast, NADH inhibits iso-citrate dehydrogenase by
directly displacing NAD+. ATP, too, is inhibitory.
 α-ketoglutarate dehydrogenase -α- Ketoglutarate dehydrogenase is inhibited by
succinyl CoA and NADH. In addition, α-ketoglutarate dehydrogenase is inhibited by a
high energy charge. Thus, the rate of the cycle is reduced when the cell has a high level
of ATP.
 Succinate dehydrogenase is inhibited by oxaloacetate, and the availability of
oxaloacetate, as controlled by malate dehydrogenase, depends on the [NADH]/[NAD+]
ratio.
目录
Glycogenesis and
Glycogenolysis
Part II
47
Non-reducing ends
Reducing
end
Structure of glycogen
Nonreducing ends:poly
Reducing end:one
12~18G
48
Distribution of glycogen
Hepatic glycogen:
The glycogen content of the liver
is up to 8% of the fresh weight.
Muscle glycogen:
The glycogen concentration
in muscle is 1-2%.
49
 Position:
Cytoplasma of liver, muscle …
1. Most anabolism of glycogen occurred
in liver and muscle.
 Definition:
The synthesis progress of glycogen from monosaccharide is named glycogenesis.
 Monosaccharide:
Glucose (main), fructose, galactose …
50
Glucose is converted to glucose 6-phosphate
ATP ADP
Glucokinase
Mg2
+
glucose
O H
H
H
H
O
H
OH
H OH
OH
CH2OH
glucose-6-
phosphate
O H
H
H
H
O
H
OH
H OH
OH
CH2OPO3H2
Glucose + ATP glucose-6-phosphate + ADP
Glucose-6-phosphate is isomerized to glucose-1-phosphate
O
H
OH
O
P
O
H
O
CH2
OH
OH
OH
O
Glucose-1-phosphate
Phosphogluco Mutase
P
O
OH
OH
O
O
CH2
OH
OH
OH
OH
Glucose-6-phosphate
51
The generation of UDP-glucose
O H
H
H
H
O
H
OH
H OH
O
CH2OH
P
O
OH
OH
glucose-1-
phosphate
UDPG
pyrophosphorylase
O H
H
H
H
O
H
OH
H OH
O
CH2OH
P
O
OH
O ÄòÜÕ
P
O
O
H
O
UDPG
(uridine diposphate glucose)
PPi
Urdine
UTP
52
The glucose in UDPG is attached to glycogen primer
ÄòÜÕ
P
P
O H
H
H
H
O
H
OH
H OH
CH2OH
UDPG
R
O
H O
O H
H
H
H
OH
H OH
CH2OH
O
O
H
H
H
H
OH
H OH
CH2OH
Gn
(Glycogen Primer)
R
O O
O H
H
H
H
OH
H OH
CH2OH
O
O
H
H
H
H
OH
H OH
CH2OH
O H
H
H
H
O
H
OH
H OH
CH2OH
Glycogen synthase
Gn+
(glycog
UDP
Urdine
α-(1,4)
53
Energy consumption
need primer
nonreducing end
glucose
G-1-P
Glycogen (1→4 and 1→6
glucose unit)
G-6-P
ATP
ADP
UDPG
UTP
PPi
Glycogen (1→4 glucose unit)
Glycogen primer
UDP
Branching enzyme
54
2. The production of glycogen degradation: glucose could replenish the blood
glucose
 Position:
Liver
 Production:
Glucose
 Glycogen-degrading
The progress that glycogen is degraded to glucose.
Glycogenolysis
Glycogen is phosphorolytic cleavaged to G-1-P
PHOSPHORYLASE Rate-limiting enzyme
Gn
Gn-1
H3PO4
O
H
OH
O
P
O
H
O
CH2
OH
OH
OH
O
glucose-1-phosphate
Gn+ H3PO4 G-1-P + Gn-1
Phosphorylase
R
O
H O
O H
H
H
H
OH
H OH
CH2OH
O
O
H
H
H
H
OH
H OH
CH2OH
Gn
(glycogen primer)
R
O O
O H
H
H
H
OH
H OH
CH2OH
O
O
H
H
H
H
OH
H OH
CH2OH
O H
H
H
H
O
H
OH
H OH
CH2OH
56
The function of
debranching enzyme
G
G-1-P
Pi
Debranching enzyme
has two activities:
α-1,4- transglycosylase
α-1,6- glycosidase
Debranching enzyme
Debranching enzyme
57
G-1-P is converted to G-6-P
O
H
OH
O
P
O
H
O
CH2
OH
OH
OH
O
glucose-1-phosphate
P
O
OH
OH
O
O
CH2
OH
OH
OH
OH
glycophosphomutase
glucose-6-phosphate
G-6-P is hydrolyzed to Glucose
glucose
O H
H
H
H
O
H
OH
H OH
OH
CH2OH
glucose-6-phosphate
O H
H
H
H
O
H
OH
H OH
OH
CH2OPO3H2
H3PO4
H2O
Glucose -6 - phosphatase
(liver)
This enzyme is deficient in brain and muscle
58
Scheme of the glycogen-
degradation
Glycogen
Gn+1
G-1-P
Pi
Gn
phosphorylase
G-6-P
glucophosphomutase
Glucose
H2O
Pi
Glucose-6-phosphatase
Catabiosis of
carbohydrate
59
 The synthesis and degradation of glycogen
UDPG pyrophosphorylase
G-1-P
UTP
UDPG
PPi
Gn+1
UDP
G-6-P Glucose
Glycogen synthase
glucophosphomutase
Hexokinase (glucokinase)
Gn
Pi
phosphorylase
Glucose-6-phosphatase(liver)
Gn
60
liver glycogen Muscle glycogen
Storage 90-100g 200-500g
≤5% 1-2%
Raw material Monosaccharide/no-
carbohydrate material
Glucose
cleavage Glucose lactate
function To maintain relatively
stable of blood glucose
To meet the energy
requirement of muscles
strenuous exercise
consumption 12-18h after meal After heavy exercise
Comparison of liver glycogen and muscle glycogen
目录
Part III
Gluconeogenesis
62
Gluconeogenesis is the synthesis progress of glucose or glucogen from
non-carbohydrate sources.
 Position:
 Substrance:
 Definition:
Cytoplasma and mitochondria of liver , kidney cells.
Pyruvate, lactate, glycerine, glycogenic amino acid.
Gluconeogenesis
Wher
e
63
Pyruvate
TCA
64
 Progress:
 Three irreversible reactions catalyzed by three key enzymes in
glycolysis must by bypassed in gluconeogenesis.
 Most reactions of gluconeogenic pathway and glycolytic pathway
are shared and reversible.
gluconeogenic pathway is the synthesis progress of glucose
from pyruvate.
①
②
65
1. Pyruvate is converted to PEP by pyruvate carboxylation bypass
Pyruvate oxalacetate PEP
ATP ADP+Pi
CO2
①
GTP GDP
CO2
②
① pyruvate carboxylase, coenzyme is biotin (in mitochondria).
② PEP-carboxykinase ( mitochondrion, cytoplasma)
66
67
Pyruvate Pyruvate
oxaloacetate
pyruvic carboxylase
ATP + CO2
ADP + Pi
Malate
NADH + H+
NAD+
Aspartate
glutamate
α-ketoglutarate
Aspartate
Malate oxaloacetate
PEP
PEP-carboxykinase
GTP
GDP + CO2
mitocondria
cytoplasma
Lactate
Alanine
NADH + H+
NAD+
NADH + H+ NAD+
ALT LDH
68
 The resource of NADH+H+ in glyconeogenesis:
The generation of glyceraldehyde-3-phosphate from 1,3-bisphosphoglycerate
need NADH+H+ in glyconeogenesis.
 NADH+H+ is provide from latate when the latate is the resource of glyconeogenesis.
 If amino amid is the resource of glyconeogenesis, NADH+H+ come from mitochondria
where NADH+H+ are derived from β- oxadation of fatty acid or TAC. The transport of
NADH+H+ dependent on the conversion of oxaloacetate and malate.
69
2. Conversion of Fructose 1,6-Bisphosphate to Fructose 6-Phosphate
3. Conversion of Glucose 6-Phosphate to Glucose
Carbohydrates Lecture.pptx
71
1. The Main Function Of Gluconeogenesis: Maintain The Stable Of Blood Glucose
 The maintenance of stable blood glucose is dependent on the gluconeogenesis from amino
acid, glycerine when fasting or starvation.
 Under normal conditions, brain utilized energy derived from glucose because brain cells could
not take energy from fatty acid; erythrocytes get the energy through glycolysis totally in
the absence of mitochondria; and, bone marrow, nerves tissure are used to take
glycolysis because of their active metabolism. Above mentioned glucose are generated
through the gluconeogenesis.
2. The Physiological Significance Of Gluconeogenesis Is To Maintain
The Stable Of Blood Glucose.
72
 The substrate of gluconeogenesis are lactate, amino acid and glycerine.
Lactate come from the muscle glycogenolysis related with exercise intensity.
Amino acid and glycerine are the substrate of gluconeogenesis when in hungry.
73
2. Gluconeogenesis is an important pathway to replenish and restore the
storage of liver glycogen
C3 pathway: After meal, most glucose is broken down to lactate or pyruvate which
contain three carbons outside the liver cells, then these C3 substrates enter the liver cells
and generate to glucogen by gluconeogenesis.
 In muscle lactate can by produced by glycolysis. Gluconeogenic capacity of muscle is very low, so
lactate diffused into blood and transported to the liver. In the liver, glucose is synthesized from
lactate by gluconeogenesis. After glucose is released into blood, it can be taken up by muscle,
which formed a cycle named Lactate cycle or Cori cycle.
 Because the enzymes in the liver and muscle are different, they could contribute to the formation
of lactate cycle.
3. Lactate cycle:
74
Active gluconeogenesis
With G-6-P
【 】
Lactate cycle (Cori cycle)
Liver Muscle
Glucose Glucose
glucose/muscle
glycogen
glycolysis
Pyruvate
Lactate
NADH
NAD+
Lactate
Lactate
NAD+
NADH
Pyruvate
gluconeo
genesis
Blood
Low gluconeogenesis
Without G-6-P
【 】
75
 Significance:
 Avoid waste of lactate
 Protect from acidosis caused by accumulation of lactate
 Lactate cycle consumes energy:
 6 ATP are needed when 2 lactate are generated to 1 glucose.
76
目录
Part IV
Other Metabolism
Pathways of Glucose
 Definition
Pentose phosphate pathway is the progress
of glucose produces pentose phosphates and
NADPH+H+, then the pentose phosphates is
converted into Glyceraldehyde 3-phosphate and
fructose 6-phosphate.
Pentose phosphate pathway produces pentose phosphates and
NADPH + H+
 Position:Cytosol
 Phase I: The Oxidative Phase
1. The Progress Of Pentose Phosphate Pathway has Two
Phases:
 The reaction has two phases:
 Phase II:The Nonoxidative Phase
Produces Pentose Phosphates, NADPH+H+ and CO2
Including a series of group transfer.
NADPH+H+
NADP+
⑴
H2O
NADP+ CO2
NADPH+H+
⑵
glucose 6-phosphate
dehydrogenase
6-phosphogluconate
dehydrogenase
C
C
C
C
COO—
CH2O
H
OH
OH
OH
H
H
HO
H
P
P
6-Phosphogluconate
H
CO
H
CH2OH
C=O
C
C
CH2O
OH
OH
H
H
P
P
Ribulose
5-phosphate
CH2OH
C O
glucose 6-phosphate
C
C
C
C
C
CH2O
H
OH
OH
OH
H
H
HO
H
H
O
P
P
6-Phosphoglucono-lactone
C
C
C
C
C=O
CH2O
H
OH
OH
H
H
HO
H
O
P
P
1.glucose 6-phosphate undergoes oxidation and to form the pentose
phosphates and NADPH
Ribose
5-phosphate
 The glucose 6-phosphate dehydrogenase which catalyze the first step is the
key enzyme of the pathway.
 H+ produced in two dehydrogenations were accepted by NADP+ to generate
NADPH + H+ .
 ribose phosphate generated in reaction is a very important intermediated
product.
G-6-P
Ribose
5-phosphate
NADP+ NADPH+H+ NADP+ NADPH+H+
CO2
 The significance of phase II is the transformation of ribose to fructose 6-
phospherate and Glyceraldehyde 3-phosphate by a series of group transfer
reaction, then enter the glycolysis. So, pentose phosphate pathway is also named
pentose phosphate shunt.
2.Enter the glycolysis by the group transfer reaction
Ribulose 5-phosphate (C5) ×3
Ribose
5-phosphate
C5
Xylulose 5-
phosphate
C5
Xylulose 5-phosphate
C5
Sedoheptulose
7-phosphate
C7
Glyceraldehyde
3-phosphate
C3
Erythrose
4-phosphate
C4
Fructose
6-phosphate
C6
Fructose
6-phosphate
C6
Glyceraldehyde
3-phosphate
C3
pentose
phosphate
pathway Phase I
Phase
II
glucose 6-phosphate(C6)×3
6-Phosphoglucono-lactone(C6)×3
6-Phosphogluconate(C6)×3
Ribulose 5-phosphate(C5) ×3
Ribose 5-phosphate
C5
3NADP+
3NADP+3H+
6-phosphogluconate dehydrogenase
3NADP+
3NADP+3H+
glucose 6-phosphate dehydrogenase
CO2
Xylulose
5-phosphate C5c
Sedoheptulose
7-phosphate C7
Glyceraldehyde
3-phosphate C3
Erythrose
4-phosphate C4
Fructose
6-phosphate C6
Fructose
6-phosphate C6
Glyceraldehyde
3-phosphate C3
Xylulose
5-phosphate C5c
Transaldolase
Transketolase
 reaction formula:
3×glucose 6-phosphate + 6 NADP+
2×Fructose 6-phosphate
+
Glyceraldehyde 3-phosphate
+
6NADPH+H+
+
3CO2
 Hydrogen receptor of dehydrogenation is NADP+ , to generate NADPH+H+。
 Transaldolase and transketolase catalyze the interconversion of three-, four-,
five-, six-, and seven-carbon sugars, with the reversible conversion of six
pentose phosphates to five hexose phosphates.
 The reaction provides specialized intermediated product: ribose 5-phosphate.
 One CO2 and two NADPH+H+ were generated by one G-6-P through one
decarboxylation and two dehydrogenation in a cycle.
Characteristic of pentose phosphate pathway:
2. The pentose phospherate pathway is regulated mainly by
the ratio of NADPH/NADP+
 Glucose-6-phosphate dehydrogenase is the key enzyme of the pentose phosphate
pathway, the activity of this enzyme decide the flow of glucose-6-phosphate which
enter the pathway.
 The G-6-P-D is inhibited by a high ratio of NADPH/NADP+ and increased
consumption of NADPH .
 Therefore, the flow of pentose phospherate pathway meets the needs of the cells
for NADPH.
3. the significance of pentose phospherate is the generation of
NADPH and ribose 5-phosphate
2.Provide NADPH as hydrogen donor to participate in various metabolic
reactions
1.Provide ribose for biosynthesis of nucleotides.
(1)NADPH is the hydrogen donor in various anabolic;
(2)NADPH participate the hydroxylation in vivo.
(3)NADPH could keep the regeneration of reduced
glutathione (GSH).
 Favism:
some people are Glucose 6-Phosphate Dehydrogenase (G6PD) deficient. their
erythrocytes will lyse after ingestion of the beans (containing divicine or other oxidizing
agents), releasing free hemoglobin into the blood (acute hemolytic anemia).
G6PD deficiency is a X-linked recessive genetic disease. X-linked diseases usually occur in
males. Males have only one X chromosome. A single recessive gene on that X
chromosome will cause the disease. The geographic distribution of G6PD deficiency is
instructive. It is common in the South than in the northern population
 NAD+ : Nicotinamide Adenine Dinucleotide
 NADP : Nicotinamide Adenine Dinucleotide Phosphate
 GTP : Guanosine Tri-Phosphate
 FADH : Flavin Adenine Dinucleotide
Thanks For
Listening …
91

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Carbohydrates Lecture.pptx

  • 1. Carbohydrates Dr. Omeed Akbar Ali P h D . C l i n i c a l B i o c h e m i s t r y T i k r i t U n i v e r s i t y - C o l l e g e o f M e d i c i n e 1
  • 2. Carbohydrates 2 Carbohydrate is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms with general formula of Cm(H2O)n CH2O (CH2O)x C6H12O6 Carbohydrates Biosynthesis Carbohydrates are predominantly biosynthesized by plants through photosynthesis. Glucose is synthesized in plants from CO2, H2O, and solar energy from the sun. chlorophyll CO2 + H2O CH2O + O2 Sunlight aldehyde
  • 3. 3 Functional groups determine function carbonyl aldehyde chlorophyll CO2 + H2O CH2O + O2 Sunlight aldehyde
  • 4. 4 Functional groups determine function carbonyl ketone
  • 5. Sugar structure  Most names for sugars end in -ose  Classified by number of carbons  6C = hexose (glucose)  5C = pentose (ribose)  3C = triose (glyceraldehyde)
  • 6. 6 Types of Carbohydrates Classification based on the number of sugar units in the total chain  Monosaccharides  Disaccharides  Oligosaccharides  Polysaccharides
  • 7. Types of Carbohydrates  Monosaccharides  Single sugar unit :  Glucose  Fructose  Disaccharides  2 monomers sugars :  Maltose  Sucrose  Lactose 7 α-(1,4) Isomaltose? α-(1,6)
  • 8. 8 Building sugars  Dehydration synthesis | fructose | glucose monosaccharides | sucrose (table sugar) disaccharide Lactose ? H2O αβ-(1,2) β-(1,4)
  • 9. Types of Carbohydrates  Oligosaccharides  up to 3-12 sugar units: - Maltotriose 9  Polysaccharides • Large polymers  > 13 sugar units:  Homo-polysaccharides are polysaccharides composed of a single type of sugar monomer. For example, Starch, Cellulose and Glycogen.  Hetero-polysaccharides are polysaccharides that contain multiple monosaccharide units. Many naturally occurring heteropolysaccharides have peptides, proteins, and lipids attached to them. Some heteropolysaccharides examples are: Peptidoglycans, Agarose and Glycosaminoglycans.
  • 10. Polysaccharides 10  Polymers of sugars  costs little energy to build  easily reversible = release energy  Function:  energy storage  starch (plants)  glycogen (animals)  in liver & muscles
  • 11. Functions of Carbohydrates  Source of energy for living beings, e.g. glucose.  Storage form of energy, e.g. glycogen in animal tissue and starch in plants.  Serve as structural component, e.g. glycosaminoglycans in humans, cellulose in plants and chitin in insects.  Non-digestable carbohydrates like cellulose, serve as dietary fibers.  Constituent of nucleic acids RNA and DNA, e.g. ribose and deoxyribose sugar.  Play a role in lubrication, cellular intercommunication and immunity.  Carbohydrates are also involved in detoxification, e.g. glucuronic acid. 11
  • 12. 12  Thus Carbohydrates are chief constituents of human food.  R.D.A for Dietary Carbohydrates= 400-600 gm/day.
  • 13. Digestion, Absorption And Transport Of Carbohydrates • The principal sites of carbohydrate digestion are the mouth and small intestine. • Digestion in Mouth: Salivary glands secrete α-amylase (ptylin), which initiates the hydrolysis of a starch. breaking some α-(1 → 4) bonds, α- amylase hydrolyzes starch into dextrins. • Digestion in Intestine: There are two phases of intestinal digestion. 1. Digestion due to pancreatic α-amylase 2. Digestion due to intestinal enzymes : sucrase, maltase, lactase, isomaltase. 13
  • 15. Absorption And Transport Of Carbohydrates Carbohydrates are absorbed as monosaccharides from the intestinal lumen. • Two mechanisms are responsible for the absorption of monosaccharides: 1. Active transport against a concentration gradient, i.e. from a low glucose concentration to a higher concentration. 2. Facilitative transport, with concentration gradient, i.e. from a higher concentration to a lower one. 15
  • 16. ADP+Pi ATP Glucose Na+ K+ Na+ PUMP Mucosal cells of Intestinal Lumen Portal Na+-dependent glucose transporter, SGLT Brush border cellular inner membrane Absorption mechanism Fructose Galactse Glucose GLUT-5 SGLT-1
  • 17. Introduction to Metabolism 17 Metabolism: The sum of the chemical changes that convert nutrients into energy and the chemically complex products of cells Hundreds of enzyme reactions organized into discrete pathways. • Substrates are transformed to products via many specific intermediates Metabolic maps portray the reactions. • Metabolism consists of catabolism and anabolism
  • 18. Introduction to Metabolism Catabolism: degradative pathways  Usually energy-yielding!  “destructive metabolism”  FUELS -> -> CO 2 + H 2 O + useful energy. Anabolism: biosynthetic pathways  Energy-requiring!  “Constructive metabolism”  Useful energy + small molecules --> complex molecules. 18
  • 19. Metabolism of Carbohydrates 19 Carbohydrate metabolism is a fundamental biochemical process that ensures a constant supply of energy to living cells. The most important carbohydrate is glucose, which can be broken down via glycolysis, enter into the Kreb's cycle and oxidative phosphorylation to generate ATP.
  • 20. Metabolic pathways  Glucose Metabolism  Glycolysis  Glycogenesis  Glycogenolysis  Gluconeogenesis  Pentose phosphate pathway  Fructose metabolism  Galactose metabolism 20
  • 22. Glycolysis 22  Glycolysis: A process in which glucose is partially broken down to two molecules of pyruvate (it is converted into lactate finally ) by cells in enzyme reactions that do not need oxygen. Glycolysis is also called anaerobic oxidation. Position of glycolysis:cytoplasm
  • 23. 23  Phase I------ glycolytic pathway: The six-carbon glucose break down into two molecules of the three-carbon pyruvate.  Phase II: Pyruvate is converted to lactate or Acetyl-CoA. 1. Glycolysis Has Two Phases: Glycolysis (Cytoplasm) Acetyl-CoA (Mitochondria)
  • 24. 24
  • 26. 26 2. Conversion of G-6-P to Fructose 6-Phosphate
  • 27. 27 3. Phosphorylation of F-6-P to F-1,6-Bisphosphate  6-phosphofructokinase-1
  • 28. 28 3. Phosphorylation of F-6-P to F-1,6-Bisphosphate  6-phosphofructokinase-1
  • 29. 4. Cleavage of Fructose 1,6-Bisphosphate +  Aldolase Enzyme
  • 30. 5. Interconversion of the Triose Phosphates
  • 31. 6. Oxidation of Glyceraldehyde 3- Phosphate to 1,3-Bisphosphoglycerate
  • 32. 7. Phosphoryl Transfer from 1,3 Bisphosphoglycerate to ADP The formation of ATP by phosphoryl group transfer from a substrate such as 1,3-bisphosphoglycerate is referred to as a substrate- level phosphorylation
  • 33. 8. Conversion of 3-Phosphoglycerate to 2-Phosphoglycerate
  • 34. 9. Dehydration of 2-Phosphoglycerate to Phosphoenolpyruvate
  • 35. ADP ATP K+ Mg2+ pyruvate kinase 10. Transfer of the Phosphoryl Group from Phosphoenolpyruvate to ADP Phosphoenolpyruvate COOH C CH2 P P O Pyruvate COOH C=O CH3
  • 36. 36
  • 37.  Position of glycolysis:cytoplasm  Glycolysis is an anaerobic process through which ATP is synthesized .  There are three irreversible steps in the process. G G-6-P ATP ADP Hexokinase ATP ADP F-6-P F-1,6-2P PFK-1 ADP ATP PEP Pyruvate Pyruvate kinase Summary of glycolysis Key Enzymes ① Hexokinase ② Phosphofructokinase-1 ③ Phosphoglycerate kinase 2. Regulation of Glycolysis: 3 key enzymes ADP ATP F-1,6-P 3- P Glycerate PGK ④ Pyruvate kinase
  • 38. 38 38 Phase II: Pyruvate is converted to lactate or Acetyl-CoA . Pyruva te COOH C=O CH3 Lacta te COOH CHOH CH3 NADH + H+ NAD+ Acetyl-CoA NADH+H+ CO2 TAC Citrate Co2 + NADH + H+ CoA-SH + NAD+
  • 39. 39 OVERVIEW  Acetyl coA, the precursor for fatty acid synthesis is produced from pyruvate, ketogenic amino acids, fatty acid oxidation and by alcohol metabolism.  It is a substrate for TCA cycle and a precursor for Oxidation , ketone bodies and faty acids.
  • 41. Definition of Tri-carboxylic Acid Cycle  The citric acid cycle is a series of reactions that brings about catabolism of acetyl-coA liberating reducing equivalents which upon oxidation through respiratory chain of mitochondria, generate ATP.  It plays a central role in the breakdown or catabolism of organic fuel molecules—i.e glucose and some other sugars, fatty acids, and some amino acids. Before these rather large molecules can enter the TCA cycle they must be degraded into a two-carbon compound called acetyl coenzyme A (acetyl CoA). Once fed into the TCA cycle, acetyl CoA is converted into carbon dioxide and energy. 41
  • 42. CoASH NADH+H+ NAD+ CO2 NAD+ NADH+H+ CO2 GTP GDP+Pi FAD FADH2 NADH+H+ NAD+ H2O H2O H2O CoA-SH CoA-SH ⑧ ① ② ③ ④ ⑤ ⑥ ⑦ ② H2O ① Citrate Synthase ② Aconitase ③ Isocitrate Dehydrogenase ④ α-ketoglutarate dehydrogenase complex ⑤ Succinyl-CoA Synthetase ⑥ Succinate Dehydrogenase ⑦ Fumarase ⑧ Malate Dehydrogenase GTP GDP ATP ADP Nucleoside Diphosphate Kinase 1. The condensation of acetyl-CoA with oxaloacetate to form citrate. 2. Formation of Isocitrate via cis- Aconitate. 3. Oxidation of Isocitrate to α- Ketoglutarate and CO2. 4. Oxidation of α-Ketoglutarate to Succinyl-CoA and CO2. 5. Conversion of Succinyl-CoA to Succinate. 6. Oxidation of Succinate to Fumarate. 7. Hydration of Fumarate to Malate. 8. Oxidation of Malate to Oxaloacetate  1. The Citric Acid Cycle Has Eight Steps
  • 43. Energetics : 2 Acetyl CoA from 2 Pyruvate  1NADH+H+ = 3/2.5 ATP  1FADH2 = 2/1.5 ATP  1GTP = 1 ATP Acetyl-CoA + 3 NAD+ + [FAD] + GDP + Pi + 2 H2O CoA-SH + 3 NADH+3 H + +[FADH2] + GTP + 2 CO2 12 ×2=24
  • 44. Indicator molecules of higher energy state i.e. ATP, NADH, citrate, Acetyl CoA – inhibit TCA cycle Indicator molecules of low energy state i.e. ADP, AMP, NAD+ – stimulate TCA cycle * * * *
  • 45.  Citrate synthase- There is allosteric inhibition of citrate synthase by ATP and long-chain fatty acyl-CoA.  Isocitrate dehydrogenase- is allosterically stimulated by ADP, which enhances the enzyme's affinity for substrates. In contrast, NADH inhibits iso-citrate dehydrogenase by directly displacing NAD+. ATP, too, is inhibitory.  α-ketoglutarate dehydrogenase -α- Ketoglutarate dehydrogenase is inhibited by succinyl CoA and NADH. In addition, α-ketoglutarate dehydrogenase is inhibited by a high energy charge. Thus, the rate of the cycle is reduced when the cell has a high level of ATP.  Succinate dehydrogenase is inhibited by oxaloacetate, and the availability of oxaloacetate, as controlled by malate dehydrogenase, depends on the [NADH]/[NAD+] ratio.
  • 47. 47 Non-reducing ends Reducing end Structure of glycogen Nonreducing ends:poly Reducing end:one 12~18G
  • 48. 48 Distribution of glycogen Hepatic glycogen: The glycogen content of the liver is up to 8% of the fresh weight. Muscle glycogen: The glycogen concentration in muscle is 1-2%.
  • 49. 49  Position: Cytoplasma of liver, muscle … 1. Most anabolism of glycogen occurred in liver and muscle.  Definition: The synthesis progress of glycogen from monosaccharide is named glycogenesis.  Monosaccharide: Glucose (main), fructose, galactose …
  • 50. 50 Glucose is converted to glucose 6-phosphate ATP ADP Glucokinase Mg2 + glucose O H H H H O H OH H OH OH CH2OH glucose-6- phosphate O H H H H O H OH H OH OH CH2OPO3H2 Glucose + ATP glucose-6-phosphate + ADP Glucose-6-phosphate is isomerized to glucose-1-phosphate O H OH O P O H O CH2 OH OH OH O Glucose-1-phosphate Phosphogluco Mutase P O OH OH O O CH2 OH OH OH OH Glucose-6-phosphate
  • 51. 51 The generation of UDP-glucose O H H H H O H OH H OH O CH2OH P O OH OH glucose-1- phosphate UDPG pyrophosphorylase O H H H H O H OH H OH O CH2OH P O OH O ÄòÜÕ P O O H O UDPG (uridine diposphate glucose) PPi Urdine UTP
  • 52. 52 The glucose in UDPG is attached to glycogen primer ÄòÜÕ P P O H H H H O H OH H OH CH2OH UDPG R O H O O H H H H OH H OH CH2OH O O H H H H OH H OH CH2OH Gn (Glycogen Primer) R O O O H H H H OH H OH CH2OH O O H H H H OH H OH CH2OH O H H H H O H OH H OH CH2OH Glycogen synthase Gn+ (glycog UDP Urdine α-(1,4)
  • 53. 53 Energy consumption need primer nonreducing end glucose G-1-P Glycogen (1→4 and 1→6 glucose unit) G-6-P ATP ADP UDPG UTP PPi Glycogen (1→4 glucose unit) Glycogen primer UDP Branching enzyme
  • 54. 54 2. The production of glycogen degradation: glucose could replenish the blood glucose  Position: Liver  Production: Glucose  Glycogen-degrading The progress that glycogen is degraded to glucose. Glycogenolysis
  • 55. Glycogen is phosphorolytic cleavaged to G-1-P PHOSPHORYLASE Rate-limiting enzyme Gn Gn-1 H3PO4 O H OH O P O H O CH2 OH OH OH O glucose-1-phosphate Gn+ H3PO4 G-1-P + Gn-1 Phosphorylase R O H O O H H H H OH H OH CH2OH O O H H H H OH H OH CH2OH Gn (glycogen primer) R O O O H H H H OH H OH CH2OH O O H H H H OH H OH CH2OH O H H H H O H OH H OH CH2OH
  • 56. 56 The function of debranching enzyme G G-1-P Pi Debranching enzyme has two activities: α-1,4- transglycosylase α-1,6- glycosidase Debranching enzyme Debranching enzyme
  • 57. 57 G-1-P is converted to G-6-P O H OH O P O H O CH2 OH OH OH O glucose-1-phosphate P O OH OH O O CH2 OH OH OH OH glycophosphomutase glucose-6-phosphate G-6-P is hydrolyzed to Glucose glucose O H H H H O H OH H OH OH CH2OH glucose-6-phosphate O H H H H O H OH H OH OH CH2OPO3H2 H3PO4 H2O Glucose -6 - phosphatase (liver) This enzyme is deficient in brain and muscle
  • 58. 58 Scheme of the glycogen- degradation Glycogen Gn+1 G-1-P Pi Gn phosphorylase G-6-P glucophosphomutase Glucose H2O Pi Glucose-6-phosphatase Catabiosis of carbohydrate
  • 59. 59  The synthesis and degradation of glycogen UDPG pyrophosphorylase G-1-P UTP UDPG PPi Gn+1 UDP G-6-P Glucose Glycogen synthase glucophosphomutase Hexokinase (glucokinase) Gn Pi phosphorylase Glucose-6-phosphatase(liver) Gn
  • 60. 60 liver glycogen Muscle glycogen Storage 90-100g 200-500g ≤5% 1-2% Raw material Monosaccharide/no- carbohydrate material Glucose cleavage Glucose lactate function To maintain relatively stable of blood glucose To meet the energy requirement of muscles strenuous exercise consumption 12-18h after meal After heavy exercise Comparison of liver glycogen and muscle glycogen
  • 62. 62 Gluconeogenesis is the synthesis progress of glucose or glucogen from non-carbohydrate sources.  Position:  Substrance:  Definition: Cytoplasma and mitochondria of liver , kidney cells. Pyruvate, lactate, glycerine, glycogenic amino acid. Gluconeogenesis Wher e
  • 64. 64  Progress:  Three irreversible reactions catalyzed by three key enzymes in glycolysis must by bypassed in gluconeogenesis.  Most reactions of gluconeogenic pathway and glycolytic pathway are shared and reversible. gluconeogenic pathway is the synthesis progress of glucose from pyruvate. ① ②
  • 65. 65 1. Pyruvate is converted to PEP by pyruvate carboxylation bypass Pyruvate oxalacetate PEP ATP ADP+Pi CO2 ① GTP GDP CO2 ② ① pyruvate carboxylase, coenzyme is biotin (in mitochondria). ② PEP-carboxykinase ( mitochondrion, cytoplasma)
  • 66. 66
  • 67. 67 Pyruvate Pyruvate oxaloacetate pyruvic carboxylase ATP + CO2 ADP + Pi Malate NADH + H+ NAD+ Aspartate glutamate α-ketoglutarate Aspartate Malate oxaloacetate PEP PEP-carboxykinase GTP GDP + CO2 mitocondria cytoplasma Lactate Alanine NADH + H+ NAD+ NADH + H+ NAD+ ALT LDH
  • 68. 68  The resource of NADH+H+ in glyconeogenesis: The generation of glyceraldehyde-3-phosphate from 1,3-bisphosphoglycerate need NADH+H+ in glyconeogenesis.  NADH+H+ is provide from latate when the latate is the resource of glyconeogenesis.  If amino amid is the resource of glyconeogenesis, NADH+H+ come from mitochondria where NADH+H+ are derived from β- oxadation of fatty acid or TAC. The transport of NADH+H+ dependent on the conversion of oxaloacetate and malate.
  • 69. 69 2. Conversion of Fructose 1,6-Bisphosphate to Fructose 6-Phosphate 3. Conversion of Glucose 6-Phosphate to Glucose
  • 71. 71 1. The Main Function Of Gluconeogenesis: Maintain The Stable Of Blood Glucose  The maintenance of stable blood glucose is dependent on the gluconeogenesis from amino acid, glycerine when fasting or starvation.  Under normal conditions, brain utilized energy derived from glucose because brain cells could not take energy from fatty acid; erythrocytes get the energy through glycolysis totally in the absence of mitochondria; and, bone marrow, nerves tissure are used to take glycolysis because of their active metabolism. Above mentioned glucose are generated through the gluconeogenesis. 2. The Physiological Significance Of Gluconeogenesis Is To Maintain The Stable Of Blood Glucose.
  • 72. 72  The substrate of gluconeogenesis are lactate, amino acid and glycerine. Lactate come from the muscle glycogenolysis related with exercise intensity. Amino acid and glycerine are the substrate of gluconeogenesis when in hungry.
  • 73. 73 2. Gluconeogenesis is an important pathway to replenish and restore the storage of liver glycogen C3 pathway: After meal, most glucose is broken down to lactate or pyruvate which contain three carbons outside the liver cells, then these C3 substrates enter the liver cells and generate to glucogen by gluconeogenesis.  In muscle lactate can by produced by glycolysis. Gluconeogenic capacity of muscle is very low, so lactate diffused into blood and transported to the liver. In the liver, glucose is synthesized from lactate by gluconeogenesis. After glucose is released into blood, it can be taken up by muscle, which formed a cycle named Lactate cycle or Cori cycle.  Because the enzymes in the liver and muscle are different, they could contribute to the formation of lactate cycle. 3. Lactate cycle:
  • 74. 74 Active gluconeogenesis With G-6-P 【 】 Lactate cycle (Cori cycle) Liver Muscle Glucose Glucose glucose/muscle glycogen glycolysis Pyruvate Lactate NADH NAD+ Lactate Lactate NAD+ NADH Pyruvate gluconeo genesis Blood Low gluconeogenesis Without G-6-P 【 】
  • 75. 75  Significance:  Avoid waste of lactate  Protect from acidosis caused by accumulation of lactate  Lactate cycle consumes energy:  6 ATP are needed when 2 lactate are generated to 1 glucose.
  • 76. 76
  • 78.  Definition Pentose phosphate pathway is the progress of glucose produces pentose phosphates and NADPH+H+, then the pentose phosphates is converted into Glyceraldehyde 3-phosphate and fructose 6-phosphate. Pentose phosphate pathway produces pentose phosphates and NADPH + H+
  • 79.  Position:Cytosol  Phase I: The Oxidative Phase 1. The Progress Of Pentose Phosphate Pathway has Two Phases:  The reaction has two phases:  Phase II:The Nonoxidative Phase Produces Pentose Phosphates, NADPH+H+ and CO2 Including a series of group transfer.
  • 80. NADPH+H+ NADP+ ⑴ H2O NADP+ CO2 NADPH+H+ ⑵ glucose 6-phosphate dehydrogenase 6-phosphogluconate dehydrogenase C C C C COO— CH2O H OH OH OH H H HO H P P 6-Phosphogluconate H CO H CH2OH C=O C C CH2O OH OH H H P P Ribulose 5-phosphate CH2OH C O glucose 6-phosphate C C C C C CH2O H OH OH OH H H HO H H O P P 6-Phosphoglucono-lactone C C C C C=O CH2O H OH OH H H HO H O P P 1.glucose 6-phosphate undergoes oxidation and to form the pentose phosphates and NADPH Ribose 5-phosphate
  • 81.  The glucose 6-phosphate dehydrogenase which catalyze the first step is the key enzyme of the pathway.  H+ produced in two dehydrogenations were accepted by NADP+ to generate NADPH + H+ .  ribose phosphate generated in reaction is a very important intermediated product. G-6-P Ribose 5-phosphate NADP+ NADPH+H+ NADP+ NADPH+H+ CO2
  • 82.  The significance of phase II is the transformation of ribose to fructose 6- phospherate and Glyceraldehyde 3-phosphate by a series of group transfer reaction, then enter the glycolysis. So, pentose phosphate pathway is also named pentose phosphate shunt. 2.Enter the glycolysis by the group transfer reaction
  • 83. Ribulose 5-phosphate (C5) ×3 Ribose 5-phosphate C5 Xylulose 5- phosphate C5 Xylulose 5-phosphate C5 Sedoheptulose 7-phosphate C7 Glyceraldehyde 3-phosphate C3 Erythrose 4-phosphate C4 Fructose 6-phosphate C6 Fructose 6-phosphate C6 Glyceraldehyde 3-phosphate C3
  • 84. pentose phosphate pathway Phase I Phase II glucose 6-phosphate(C6)×3 6-Phosphoglucono-lactone(C6)×3 6-Phosphogluconate(C6)×3 Ribulose 5-phosphate(C5) ×3 Ribose 5-phosphate C5 3NADP+ 3NADP+3H+ 6-phosphogluconate dehydrogenase 3NADP+ 3NADP+3H+ glucose 6-phosphate dehydrogenase CO2 Xylulose 5-phosphate C5c Sedoheptulose 7-phosphate C7 Glyceraldehyde 3-phosphate C3 Erythrose 4-phosphate C4 Fructose 6-phosphate C6 Fructose 6-phosphate C6 Glyceraldehyde 3-phosphate C3 Xylulose 5-phosphate C5c Transaldolase Transketolase
  • 85.  reaction formula: 3×glucose 6-phosphate + 6 NADP+ 2×Fructose 6-phosphate + Glyceraldehyde 3-phosphate + 6NADPH+H+ + 3CO2
  • 86.  Hydrogen receptor of dehydrogenation is NADP+ , to generate NADPH+H+。  Transaldolase and transketolase catalyze the interconversion of three-, four-, five-, six-, and seven-carbon sugars, with the reversible conversion of six pentose phosphates to five hexose phosphates.  The reaction provides specialized intermediated product: ribose 5-phosphate.  One CO2 and two NADPH+H+ were generated by one G-6-P through one decarboxylation and two dehydrogenation in a cycle. Characteristic of pentose phosphate pathway:
  • 87. 2. The pentose phospherate pathway is regulated mainly by the ratio of NADPH/NADP+  Glucose-6-phosphate dehydrogenase is the key enzyme of the pentose phosphate pathway, the activity of this enzyme decide the flow of glucose-6-phosphate which enter the pathway.  The G-6-P-D is inhibited by a high ratio of NADPH/NADP+ and increased consumption of NADPH .  Therefore, the flow of pentose phospherate pathway meets the needs of the cells for NADPH.
  • 88. 3. the significance of pentose phospherate is the generation of NADPH and ribose 5-phosphate 2.Provide NADPH as hydrogen donor to participate in various metabolic reactions 1.Provide ribose for biosynthesis of nucleotides. (1)NADPH is the hydrogen donor in various anabolic; (2)NADPH participate the hydroxylation in vivo. (3)NADPH could keep the regeneration of reduced glutathione (GSH).
  • 89.  Favism: some people are Glucose 6-Phosphate Dehydrogenase (G6PD) deficient. their erythrocytes will lyse after ingestion of the beans (containing divicine or other oxidizing agents), releasing free hemoglobin into the blood (acute hemolytic anemia). G6PD deficiency is a X-linked recessive genetic disease. X-linked diseases usually occur in males. Males have only one X chromosome. A single recessive gene on that X chromosome will cause the disease. The geographic distribution of G6PD deficiency is instructive. It is common in the South than in the northern population
  • 90.  NAD+ : Nicotinamide Adenine Dinucleotide  NADP : Nicotinamide Adenine Dinucleotide Phosphate  GTP : Guanosine Tri-Phosphate  FADH : Flavin Adenine Dinucleotide