Transcript carbohydrates

Carbohydrates
Lectures for Medical and Dentist Students
1st Year Course, Spring Semester, 2009
Semmelweis University, Department of
Medical Biochemistry
Presented by dr. András Hrabák, Department
of Medical Chemistry, Molecular Biology
and Pathobiochemistry
CARBOHYDRATES
What are carbohydrates ? - Polyhydroxy-oxo compounds
Grouping principles:
1. According to the size of the molecules (i.e. the number of units)
- monosaccharides, oligosaccharides, polysaccharides
2. According to the number of carbon atoms in monosaccharides
- trioses, tetroses, pentoses, hexoses, heptoses etc.
3. According to the carbonyl group
- aldoses (aldehyde group), ketoses (keto group)
Significances:
1. Energy storage - homopolysaccharides
2. Structure material - heteropolysaccharides, cellulose
3. Intermediates in the metabolism - smaller sugars
4. Miscellaneous
Structural characteristics: aldehyde group is always at the end of the molecule
(C-1); keto group is theoretically positioned anywhere in the middle of the chain,
however, in biologically important ketoses it is at C-2 position
Monosaccharides:
O=C-H

H - C - OH

CH2OH
CH2OH

C=O

CH2OH
O=C-H
O=C-H
CH2OH



H - C - OH HO - C - H
C=O



H - C - OH
H - C - OH H - C - OH



CH2OH
CH2OH
CH2OH
D-glyceraldehyde dihydroxyacetone D-erythrose
D-treose
D-erythrulose
aldotriose
ketotriose
aldotetroses
ketotetrose
Chirality and chiral centers in monosaccharides:
The number of possible chiral isomers of a monosaccharide can be
calculated by 2n where n is the number of chiral centers.
A monosaccharide belongs to the D-series if the configuration of the
chiral center closest to the primary alcoholic OH-group is identical to
that of the chiral carbon of the D-glyceraldehyde.
Explanation: if the groups written over the indicated chiral carbon are oxidized
and eliminated as CO2, except the neighbouring, whose -OH is oxidized to
aldehyde, the product is glyceralderhyde containing only one chiral carbon.
Therefore, each bigger monosaccharide can be decomposed into D- or Lglyceraldehyde, whose chiral -OH group corresponds to the -OH neighbouring
to the primary alcoholic group (or, generally to the OH in the largest distance
to the aldehyde/keto group).
R(S) nomenclature of monosaccharides: more complicated, not used
frequently, because each chiral center must be characterized separately
(too long names, etc.)
Biologically important monosaccharides usually belong to D-series
(exceptions: L-fucose, L-iduronate)
Optical rotations: its direction is independent on the D- or L-configuration
e.g. D-dlucose is dextrorotatory, D-fructose is levorotatory.
Enantiomers: complete mirror images, in which each chiral centers are
of different configurations, e.g. D- and L-glucose
Diastereomers: partial mirror images in which the deciding OH-group is
usually of D-configurations, but other hydroxyl groups may be in different
positions.
Biologically important pentoses and hexoses:
Pentoses:
O=C-H

H- C - OH

H- C - OH

H- C - OH

CH2OH
D-ribose
O=C-H

H - C - OH

HO- C - H

H- C - OH

CH2OH
D-xylose
CH2OH

C=O

H- C - OH

H- C - OH

CH2OH
D-ribulose
CH2OH

C=O

HO- C - H

H- C - OH

CH2OH
D-xylulose
O=C-H

HO- C - H

HO- C - H

H- C - OH

H- C - OH

CH2OH
D-mannose
CH2OH

C=O

HO- C - H

H- C - OH

H- C - OH

CH2OH
D-fructose
Hexoses:
O=C-H

H- C - OH

HO- C -H

H- C - OH

H- C - OH

CH2OH
D-glucose
O=C-H

H - C - OH

HO- C - H

HO- C - H

H- C - OH

CH2OH
D-galactose
Epimers:
sugar pairs in
which only one
chiral center has
different
configuration,
e.g. glucose and
galactose
Mutarotation, formation of cyclic monosaccharides (hemiacetals):
It is based on the reaction of the aldehyde or keto group with a hydroxyl group
appropriately positioned to form a five- or six-membered cyclohemiacetale or
cyclohemiketale ring. Reaction type is an intramolecular nucleophilic addition.
HO - C - H

H - C - OH

HO - C - H
O

H - C - OH

H-C

CH2OH
 -D-glucose (67 %)
O=C-H

H - C - OH

HO - C - H

H - C - OH

H - C - OH

CH2OH
open chain form
H - C - OH

H - C - OH

HO - C - H
O

H - C - OH

H-C

CH2OH
 -D-glucose (33 %)
Consequences: the appearance of a new chiral center at C-1 position and the existence of two
new D-glucose isomers (anomers) which are in equilibrium with each other and with the
open chain form. Optical rotation is changed during the process (e.g. dissolution of glucose in
water), this is the explanation of the name „mutarotation”.
Pyranose and furanose rings: stable steric structures are possible if the number
of the ring atoms is 5 or 6. As pyrane is a six-membered ring containing one
oxygen, while furane is similar with a five-membered ring, the cyclohemiacetale
or cyclohemiketale sugar rings are called as „pyranose” (6-membered) or
„furanose” (5-membered) structures. Pyranose is characteristic of aldohexoses
while furanose is typically found in pentoses and ketohexoses.
Anomers: Chiral isomers differing only in the position of carbonyl-derived
hydroxyl group (glycosidic hydroxyl). If its position is identical to the
D-configuration of the determining carbon of the projected formula, it is called
as –anomer, while in the case of identity with L-configuration, it is –anomer.
Anomers are in equilibrium and they can be transformed freely to each other,
differently from other chiral isomers.
Representation rules of cyclic sugars:
1.The oxygen atom of the hemiacetal/ketale ring is written into the upper right
position of pyranose or in the uppest position of furanose rings.
2. Hydroxyl groups written on the right side of the carbon chain in open-chain
model, have to be drawn below the ring plane.
3. The CH2OH group should be written over the ring plane in the case of Dsugars (and opposite for L-isomers).
Hemiacetal ring structures of - and -D-glucose:
CH2OH
CH2OH
O
OH
O
OH
OH
OH
OH
OH
OH
OH
-D-glucose
-D-glucose
The structures above cannot show the possible conformations.
CH2OH
CH2OH
HO
HO
O
O
HO
HO
OH
OH
OH
OH
-D-glucopyranose (1-OH axial)
-D-glucopyranose (1-OH equatorial)
-D-glucopyranose is more stable (~63 %), because all of its
hydroxyl groups are in equatorial position; equilibrium is shifted
to right.
Different endo-conformations of furanose rings in nucleic acids
O
O
HOH2C
OH
HOH2C
OH
,
,
2
HO
2’-endo--D-deoxyribofuranose
3
HO
OH
3’-endo--D-ribofuranose
2’-endo--D-deoxyribofuranose is characteristic of B-DNA,
3’-endo--D-ribofuranose conformation is typical in A-DNA
and in RNA.
Reaction of carbohydrates I.
1. Reduction and oxidation
2. Ester formation
3. Ether formation
4. Glycoside formation
5. Isomerization
1a. Reduction of carbohydrates: aldehyde or keto group is reduced into primary
or secondary alcoholic hydroxyl group, respectively. The product is called
sugar alcohol (hexitol, pentitol). Glucose, or fructose are reduced to sorbitol.
O=C-H

H - C - OH

HO - C -H

H - C - OH

H - C - OH

CH2OH
D-glucose
CH2OH

H - C - OH

HO - C -H

H - C - OH

H - C - OH

CH2OH
D-sorbitol
CH2OH

C=O

HO - C -H

H - C - OH

H - C - OH

CH2OH
D-fructose
Reactions of carbohydrates II.
1b. Oxidations of monosaccharides
- primary alcoholic group is oxidized
- aldehyde group is oxidized
- both terminal groups are oxidized
uronic acid
aldonic acid
aldaric acid
O=C-H
O=C-H


H - C - OH

HO - C - H

H - C - OH

H - C - OH

COOH
D-glucuronic acid
H - C - OH

HO - C - H

H - C - OH

H - C - OH

CH2OH
D-glucose
COOH

H - C - OH

HO - C - H

H - C - OH

H - C - OH

CH2OH
D-gluconic acid
Significances: glucuronic acid is involved in biotransformations making
compounds more hydrophilic by glucuronide formation. Phosphate ester of
gluconic acid is an important intermediate of pentose phosphate cycle.
Uronic acids are also building blocks of heteropolysaccharides.
2. Ester formation: alcoholic hydroxyl groups can react with acids
forming esters. Important reactions: intramolecular lactone formation.
COOH

H - C - OH

HO - C - H

H - C - OH

H - C - OH

CH2OH

C=O

H - C - OH

HO - C - H

H - C - OH

H-C

CH2OH
O
D-gluconic acid and
its lactone form (on
the right)
3. Ether formation: alcoholic groups can react with each other forming ethers.
4. Glycoside formation: involves the participation of glycosydic
hydroxyl group.
Glycosydic hydroxyl group is distiguished from other hydroxyl groups. They are
derived from an aldehyde/keto group by the formation of an intramolecular hemiacetal
or hemiketale in a reversible reaction. Therefore, glycosydic OH-group is a hidden
aldehyde/keto group, which is more reactive compared to other hydroxyl groups.
This group can form special glycosidic ethers (glycosides) or esters. Oligo- and
polysaccharides are also glycosides.
Glycoside formation: e.g. –D-glucose reacting with another –D-glucose leads to the
formation of maltose:
CH2OH
CH2OH
O
O
HO
OH
OH
OH
HO
-H O
2
OH
CH2OH
OH
OH
CH2OH
O
O
O
HO
OH
OH
OH
Two glucose molecules react with each other; one of them (showing on the left side)
participates in the reaction with its glycosidic –OH group, forming a glycosidic ether or
glycoside. The other glucose (right side) participates with an ordinary secondary
alcoholic hydroxyl group. The product is called glycoside, also considered as an
acetale (from chemical aspect), which is a disaccharide, this one is called maltose.
Polysaccharides are also formed via glycosidic bonds between monosaccharide units.
Reactions of sugars with acids and bases
1. Strong acids cause the dehydration of pentoses to furfural and that of hexoses to
hydroxymethylfurfural:
OH
HO
H+
-
HO
O
aldopentose
nH2O
CH2OH
CHO
O
furfural
2. In basic environment, monosaccharides may be isomerized. During this process
enolate anion is formed by proton movement:
H-C=O
|
HO - C - H
mannose
|
R
H
|
H-C=O
H - C - OH
H - C - OH
|
||
|
H - C - OH
C - OH
C=O
glucose
|
|
|
fructose
R
R ene-diol
R
Deoxy sugars:
H-C=O

CH2

H - C - OH

H - C - OH

CH2OH
2-deoxy-D-ribose
H-C=O

HO - C - H

H - C - OH

H - C - OH

HO - C - H

CH3
L-fucose
H-C=O

CH2

HO - C - H

H - C - OH

H - C - OH

CH2OH
2-deoxy-D-glucose
Amino sugars (in natural amino sugars, amino group is found in position 2)
H-C=O

H - C - NH2

HO - C - H

H - C - OH

H - C - OH

CH2OH
D-glucosamine
H-C=O

H - C - NH2

HO - C - H

HO - C - H

H - C - OH

CH2OH
D-galactosamine
H-C=O

NH2 - C - H

HO - C - H

H - C - OH

H - C - OH

CH2OH
D-mannosamine
N-acetylated sugar derivatives:
H-C=O
H-C=O
COOH



H - C - NH - CO-CH3
H - C - NH - CO - CH3
C=O



HO - C - H
CH3 - CH - O - C - H
CH2




H - C - OH
HOOC
H - C - OH
CH3 H - C - OH




H - C - OH
H - C - OH
CO - NH - C- H



CH2OH
CH2OH
OH - C - H
N-acetyl-D-glucosamine
N-acetyl-D-muramic acid

Muramic acid: N-acetyl-D-glucosamine bearing lactic acid
H - C - OH
by an ether bond at C-3 position

Sialic acid: N-acetyl-mannosamine connected to pyruvic acid
H - C - OH
at C-1 position

Function of deoxy and amino sugars:
CH2OH
sialic acid
Deoxyribose is a component of DNA, fucose is found in the carbohydrate moieties
of glycoproteins; 2-deoxy-D-glucose is used in research.
Acetylated amino sugars are the components of heteropolysaccharides,glycoproteins,
blood group and histocompatibility antigens
Functions of sugar alcohols and acids:
Ribitol is a component of riboflavin (vitamin B2). Sorbitol is used as a sweeting
agent instead of glucose or sucrose (diabetes!)
D-glucuronic acid is important in biotransformation and together with other uronic
acids are components of mucopolysaccharides. L-ascorbic acid is Vitamin C. Dglyceric acid is important in glycolysis and its bis-phosphate ester is a regulator of
oxygen binding of hemoglobin.
Sugar phosphates (phosphate esters)
H-C=O
CH2 - O- PO3H2
COOH
COOH




H - C - OH
C=O
H - C - OH
H - C - PO3H2




HO - C - H
HO - C - H
CH2- O-PO3H2 CH2 - O - PO3H2


3-phosphoglycerate 2,3-bisphosphoglycerate
H - C - OH
H - C - OH


Functions of phosphate esters:
H - C - OH
H - C - OH
important intermediates of glycolysis and


other processes of carbohydrate metabolism
CH2 - O - PO3H2 CH2 - O - PO3H2
glucose-6-phosphate fructose-1,6-bisphosphate
Sugar alcohols:
CH2OH
|
H - C - OH
|
H - C - OH
|
H - C - OH
|
CH2OH
D-ribitol
CH2OH
|
H - C- OH
|
HO - C - H
|
H - C - OH
|
H - C - OH
|
CH2OH
D-sorbitol
CH2OH
|
H - C - OH
|
H - C - OH
|
CH2OH
CH2OH
|
H - C - OH
|
CH2OH
D-erythritol
Uronic and aldonic acids:
H-C=O
|
H - C - OH
|
HO - C - H
|
H - C - OH
|
H - C - OH
|
COOH
D-glucuronic acid
O=C
|
HO - C
||
O
HO - C
|
H-C
|
HO - C - H
|
CH2OH
L-ascorbic acid (lactone)
COOH
|
H - C - OH
|
CH2OH
D-glyceric acid
glycerol
Disaccharides I.
They are composed of monosaccharides by glycosidic bondings
containing 2-10 monosaccharide units
1
O
4
OH
OH
OH
OH
OH
maltose
OH
OH
O
O
O
OH
CH2OH
CH2OH
CH2OH
O
1
4 OH
OH
O
OH
OH
CH2OH
cellobiose
Maltose and cellobiose are reducing disaccharides composed of two
-D-glucoses and -D-glucoses, respectively, via 1-4 glycosidic
bonds.
Disaccharides II.
Lactose (milk sugar) and saccharose (sucrose, cane sugar):
CH2OH
OH
CH2OH
OH
O
OH
O
1
O
OH
4 OH
OH
1
O
O
HOH2C
O
2
HO
5
CH2OH
OH
OH
lactose
CH2OH
OH
OH
saccharose (sucrose)
Lactose is a reducing disaccharide composed of a -D-galactose and a
-D-glucose via 1,4-glycosidic bond. Sucrose is a non-reducing disaccharide composed of an -D-glucose and a -D-fructose via a 1,2glycosidic bond.
Disaccharides III.
Reducing and non-reducing disaccharides:
If a saccharide contains a free aldehyde or glycosidic (hidden
aldehyde) group, it can reduce various reactants, e.g. Cu2+ or Ag+ions. Sugars lacking these free aldehyde or glycosidic hydroxyl
groups fail to reduce these ions. In non-reducing disaccharides,
their glycosidic bonding has been formed with the participation of
both glycosidic hydroxyl groups. Consequently, non-reducing
disaccharides nor did show mutarotation, also requiring the
presence of free aldehyde (or glycosidic -OH) group.
Biological importance of disaccharides:
Lactose: the most abundant disaccharide in the milk.
Sucrose (saccharose): the most important sugar in nutrition in the
civilized world.
Maltose and cellobiose are structural units and degradation
products of starch and cellulose, respectively.
Polysaccharides (glycans)
Polysaccharides contain more than 10 monosaccharide units linked by glycosidic bonds.
They may be homopolysaccharides composed of one type of monosaccharides or heteropolysaccharides composed of more than one type of monosaccharides and their units are
di- or oligosaccharides.
Biologically important homopolysaccharides:
Name
Monosaccharide unit
Linkage
Found in
Starch
-D-glucose
amylose
-1,4
plants
amylopectine
-1,4; -1,6
plants
Glycogene
-D-glucose
-1,4; -1,6
liver, muscle
Cellulose
-D-glucose
-1,4
plants
Inulin
-D-fructose
-1,6
plants
Dextrane
-D-glucose
-1,6
bacteria
Significance: Starch and glycogen are energy stores in plants and animals, respectively,
degraded by amylase and phosphorylase into glucose and glucose-1-phosphate units,
respectively. The -1,6-bonding is splitted by -1,6-glycosidases. Cellulose is the most
important structural polysaccharide in the plant cell wall. It is degraded by cellulase
produced by bacteria and snails only. Inulin is used to determine the blood volume,
dextrane is used for gel filtration after sulfation with H2SO4.
Amylose - disaccharide unit of
-D-glucoses, 1,4-bonding
CH2OH
CH2OH
O
O
OH
1
O
O
4
OH
O
OH
OH
n
CH 2 OH
Amylopectin and glycogen tetrasaccharide unit of -Dglucoses including a branching
point, 1,4 and 1,6-bonding
OH
branching point
O
amylopectin 24-30
glycogen 8-12
O
CH 2OH
OH
O
OH
O
OH
CH2OH
OH
O
OH
O
O
OH
CH2OH
O
OH
OH
O
OH
O
OH
OH
CH 2OH
CH 2O
O
O
Cellulose - trisaccharide unit of
-D-glucoses, 1,4-bonding
HO
O
CH2OH
O
O
OH
O
Important heteropolysaccharides
Name
Major monosaccharides
Linkage
Hyaluronic acid D-glucuronic acid and
-1,3; -1,4
N-acetyl-D-glucosamine
Chondroitin
D-glucuronic acid and
-1,3; -1,4
N-acetyl-D-galactosamine
kDa size
Found in
3-8000
synovial fluid
cartilage, skin
cornea, bone
vascular wall,
skin
5-50
- sulfate A
4-sulfate ester
- sulfate C
6-sulfate ester
Dermatan sulfate L-iduronic acid and
-1,3; -1,4
15-40
N-acetyl-D-galactosamine 4-sulfate ester
Keratan sulfate D-galactose and
-1,3; -1,4
4-20
N-acetyl-D-glucosamine 4-sulfate ester
Heparin (sulfate) L-iduronic acid
-1,4
6-25
N-acetyl-D-glucosamine 2-sulfate ester
D-glucuronic acid
(6-sulfate ester)
Bacterial cell wall N-acetyl-muramic acid
-1,4
polysaccharide N-acetyl-D-glucosamine
skin, heart
vascular wall
cartilage
cornea
cartilage
heart , muscle
mast cell, liver
bacterial
cell wall
Heteropolysaccharides I.
Hyaluronic acid - disaccharide unit, -1,3-bonding in the unit
CH2OH
COOH
OH
O
O
O
O
O
OH
OH
NH - CO - CH3
D-glucuronic acid
n
N-acetyl-D-glucosamine
Chondroitin-4(6)-sulfate - disaccharide unit, -1,3-bonding in the unit
6-sulfate
CH2OH
COOH
OH
O
-O3S-O
O
O
OH
D-glucuronic acid
O
O
NH - CO - CH3
n
N-acetyl-D- galactosamine
Dermatan sulfate - -1,3-bonding
CH2OH
O
O
OH
COOH
OH
-O S-O
3
O
O
O
NH-CO-CH3
n
L-iduronic acid
N-acetyl-D-galactosamine4-sulfate
Keratan sulfate I; in keratan sulfate II N-acetyl D-galactosamine
is instead of D-galactose - disaccharide unit, -1,3-bonding
CH2O-SO3-
CH2OH
HO
O
O
O
O
OH
OH
O
NH-CO-CH3
n
D-galactose
N-acetyl-D-glucosamine6-sulfate
Heparin; disaccharide unit, -1,4,-bonding
CH2-O-SO3-
O
OH
O
O
OH
COOH
O
O
NH-SO3-
O-SO3-
n
D-glucosamine-N-sulfate
6-sulfate
L-iduronic acid2-sulfate
Glycoproteins and proteoglycans
Covalent conjugates of proteins and carbohydrates. In glycoproteins,
the protein part is bigger, while in proteoglycans the size of the polysaccharide is definitive. They are different in certain aspects:
Proteoglycan
Found in
carbohydrate
monosaccharide units/molecule
repeating unit
branching
hexuronic acid
Glycoprotein
cartilage, bone
membranes, body fluids
glycosaminoglycan
oligosaccharide
> 50
< 25
disaccharide
no
no
yes
found
not found
The carbohydrates are linked to protein via special amino acid side chains. The
most frequent glycopeptide bonds are the N-glycosidic bond via asparagine side
chains and the O-glycosidic bonds via serine or threonine residues. The most
frequent sugars in glycoproteins are mannose, glucose, galactose, N-acetylated
hexosamines, sialic acid, L-fucose. Proteoglycans contain heteropolysaccharides.
Glycoproteins and proteoglycans II.
In the figure below the two specific glycopeptide bonds are shown.
HOH 2 C
O
CO
OH
HO
CO-CH 3
HOH 2 C
HO
protein
NH-CO-CH 2 -CH
NH
A
NH
CO
O
protein
O-CH-CH
OH
NH
CH 3
NH
B
CO-CH 3
In bacterial cell walls, where the muramic acid has a lactic side chain
which can be esterified, a tetrapeptide is linked to this part of the
molecule (L-Ala-D-Glu-L-Lys-D-Ala) and the peptidoglycan chains
are linked to each other by pentaglycine bridges between L-Lys -NH2
side chains and D-Ala COOH terminals (by amide bondings)
Glycolipids and lipopolysaccharides
Covalent conjugates of lipids and carbohydrates. The most known example is the
ABO blood group system where a penta- or hexa-saccharide unit is linked to the
sphingosine part of a ceramide and the specificity is determined by the composition of
the carbohydrate moiety.
Lipopolysaccharides (LPS) are known as bacterial endotoxins. They may cause
serious septic shock because LPS induces the inducible nitric oxide synthase enzyme
in various cells resulting in a high NO level causing a dramatic decrease of blood
pressure leading to death. LPS is also involved in the initiation of inflammatory
responses.
O
NH3+
P
HO
O
HO
O
O
O
O
O
O
C14
O
C14
O
O
C14
O
C14
C12
O
O
O
C14
C16
NH3+
O
O
NH
OH
O
P
P
O
O NH
OH
O-
O-
O
O
Salmonella
LPS
lipid A
O
O
HO
O-
Blood group antigens; AB0 system, 0 antigen right down
CH2OH
HO
OH
CH2OH
O
O
O
HO
NH-CO-CH3
A-antigen: N-acetyl-galactosamine
CH2OH
HO
OH
O
O
HO
-1,3
HO
-1,3
O
CH2OH
O
O
HO
CH3
-1,2
NH-CO-CH3
O
O
OH
H(O)-antigen:
OH
B-antigen: D-galactose
----galactose-N-acetyl-glucosamine
L-fucose
Analysis of carbohydrates
Classical protocol:
1. Isolation and purification
2. Polysaccharide or not ? – positive Lugol reaction indicates starch or glycogen
3. If not, disaccharide or not ? – positive Barfoed probe suggests monosaccharide or
reducing disaccharide. Maltose and lactose are distinguished by their different
fermentation.
4. If monosaccharide, pentose or hexose – pentose is detected by Bial-orcin reaction
5. For hexose, aldose, or ketose – Seliwanoff-reaction positivity indicates fructose
6. Aldohexose – glucose and galactose are fermented differently
More detailed analysis is possible using more sophisticated chemical methods
including various hydrolytic processes, methylation, osazone formation.
Recent protocol: Gas chromatography, HPLC and the study of various bondings by
spectroscopic methods. These are chemical methods.
Blood glucose content is a very important indicator of metabolic homeostasis. It can
be measured by a kit based on the specific oxidation of glucose by glucose oxidase
enzyme. This reaction requires FAD coenzyme, which is reoxidized forming peroxide.
Peroxide is removed by peroxidase enzyme, using a chromofor substrate, finally the
oxidation of the substrate is accompanied by a color formation measured by spectrophotometer. Using a glucose standard with known glucose concentration, the glucose
content of blood samples can be calculated. Normal range of blood sugar content is
3.3-5.5 mM. It is strictly regulated by various hormones (details in 2nd year)
Role of a hexose phosphate in the regulated reaction of glycolysis
O
O
-O -P -O -H C
2
O
O OH
OH
-
+
-
ATP
ATP
-O -P-O -H C
2
O
OH
-
CH2
CH OH
2
OH
fructose-6-phosphate
O OH
OH
O
-O -P-O
O
-
-
fructose-1,6-bisphosphate
enzyme: phosphofructokinase I
PFK-I is inhibited allosterically by ATP, which is the end product of
glycolysis, activated by ADP and AMP. It is also activated by fructose2,6-bisphosphate, produced by PFK-II.
Role of a pentose phosphates in the catabolism of glucose in liver
CH2OH
CH2OH
H-C=O
C=O
H-C-OH
HO-C-H
+
H-C-OH
2CH2O PO3
H-C-OH
H-C-OH
2CH2O PO3
xylulose-5-phosphate ribose-5-phosphate
H-C=O
C=O
HO-C-H
+
H-C-OH
H-C-OH
-
CH2-O-PO32
H-C-OH
H-C-OH
2CH2O PO3
sedoheptulose-7-phosphate
glyceraldehyde-3-phosphate
enzyme: transketolase
This is a reaction of pentose phosphate pathway, an alternative glucose
catabolic route, contributing to NADPH and pentose synthesis.
Role of a sugar phosphate in the synthesis of a sugar nucleotide
O
N
O
O
N
O
CH2OH
2-
O
CH2-O-P-O-P-O-PO32
-
-
HO
OH
OH
OH
OH
O
+
O
O
O3P-O
uridine-triphosphate (UTP)
O
glucose-1-phosphate
UDP-glucose synthetase
N
O
O
N
O
CH2-O-P-O-P-O
-
O
OH
CH2OH
O
OH
UDP-glucose
O
+
HO
-
O
OH
-
O
-
O
O=P-O-P=O
-
O
-
O
OH
pyrophosphate
ATTENTION!
The material of carbohydrate lectures will be presented onto the
website of the Department of Medical Biochemistry.
You may try to read it and to save it onto your own pendrive after
searching the following website:
www.biokemia.sote.hu, for students
Medical Chemistry II.
authorized pages, username: file; Password: open2;
In the case of any troubles write an e-mail to Dr. István Léránt to the
address of [email protected]
Filename: carblec.ppt
Software needed: Office/PowerPoint
Recommended material: Lehninger book, list of carbohydrate
structures created by Dr. Zsolt Rónai.
Have a good learning,
dr. A. Hrabák