cho for pkk 5203
TRANSCRIPT
-
8/7/2019 CHO for PKK 5203
1/51
CARBOHYDRATES STRUCTURE
AND FUNCTIONS
-
8/7/2019 CHO for PKK 5203
2/51
Carbohydrates (CHO) is widely distributed in
plants and animals. They have important
structural and metabolic roles.
In plants:Glucose synthesised from CO2 and H2O by photosynthesis.
In animal:Animal synthesise CHO from lipid, glycerol and amino acid.
Most animal CHO derived from plants.
Milk is the only animal-derived food that contains significant
carbohydrate
Glucose: The most important CHO
Most dietary CHO absorbed into the blood stream.
Other sugars are converted into glucose in the liver.
Major metabolic fuel of mammals except ruminant.
Universal fuel for fetus.
-
8/7/2019 CHO for PKK 5203
3/51
Carbohydrate functions:
Carbohydrates provide the majority of energy in
most organisms (simple CHO are sugars, complex
CHO can be broken down into simple sugars)CHO are structural components of cell walls and
cell membranes.
CHO serves as metabolic intermediates (eg.
Glucosephosphate)
CHO (eg, ribose, deoxyribose) are components ofthe nucleotides that form DNA and RNA.
CHO play roles in lubrication, cellular
intercommunication, and immunity.
-
8/7/2019 CHO for PKK 5203
4/51
Sugar Where found Biochemical importance
D- ribose
D- ribulose
D-xylose
D-arabinose
D-lyxose
D-xylulose
Nucleic acid
Formed in metabolic
processes
Wood gums,proteoglycan,
glycosaminoglycan
Gum arabic, plum
and cherry gums
Heart muscle
Intermediate in
uronic acid pathway
Structural element of nucleic
acids
Ribulose phosphate is an
intermediate in pentose
phosphate pathway.
Constituents of glycoproteins
Constituents of glycoprotein
A constituent of a lyxoflavin
isolated from heart muscle.
-
8/7/2019 CHO for PKK 5203
5/51
- Carbohydrates are essential to all living organisms and are
the most abundant class of biological molecules.
- They are the end products of photosynthesis (100 billion
tons of CO2 + H2O/yearp cellulose and other plant
products.
- The metabolic breakdown of monosaccharides providesmost of the energy used to power biological processes.
- In structural material (cell walls, connective tissue)
- Important for cell signalling, cell-cell interactions
- Chemically, they are polyhydroxyl aldehydes or ketones.
- Contain three elements - C, H, O, many according to theformula (CH2O)n; where n 3.
- Greek saccharon means sugar
-
8/7/2019 CHO for PKK 5203
6/51
CHO Classification and nomenclature
1. Monosaccharides (eg. glucose) are simple sugars. They maybe connected by glycosidic linkages to form the following
glycosides.
a) disaccharides (eg. Sucrose are composed of two
monosaccharides.
b) Oligosaccharides (eg, blood group antigens) are composedof two to ten monosaccharides.
c) Polysaccharides (eg, glycogen) are composed of more than
10 monosaccharides.
2. Aldoses and ketoses:
The reactive group (ie, aldehyde or ketone) on a CHOdetermines whether it is and aldose or a ketose.
a) Aldoses, (eg, glucose) possess a reactive group aldehyde
(CHO) group.
b) ketoses (eg, fructose) possess a reactive ketone (C O)
group.
-
8/7/2019 CHO for PKK 5203
7/51
-
8/7/2019 CHO for PKK 5203
8/51
Nomenclature
Carbon numbering system. In the general
formula for monosaccharides
(CH2O)n (n=number of carbons). Carbons are
numbered sequentially with the carbon
possessing the aldehyde or ketone group
assigned the lowest possible number.
The total number of carbons determines whether
a monosaccharides is a triose (3C), a tetrose
(4C), a pentose (5C) or hexose (6C). Monosaccharide and reactive- group names can
be combined to designated compounds. Eg,
glucose is an aldohexose (ie, a hexose
possessing an aldehyde group.
-
8/7/2019 CHO for PKK 5203
9/51
aldotriose ketotriose
-
8/7/2019 CHO for PKK 5203
10/51
Glyceraldehyde
Glyceraldehyde
Is an aldotriose C
C
O H
CH2OHOHH
Glyceraldehyde exists in two
stereoisomeric forms because the
starred carbon is a stereocenter (chiral carbon):
it has four different groups attached.
-
8/7/2019 CHO for PKK 5203
11/51
Monosaccharide stereoisomers
When the number ofchiral carbon atoms increases in
optically active compound the number of possible
optical isomers also increases.
A compound with n chiral carbon atoms has a
maximum of 2n possible stereoisomers.
Aldose have 2n-2
Aldose has two achiral carbons (C1 and C6).
Ketose have 2n-3
Ketose has three achiral carbons (C1, C2, and C6)
-
8/7/2019 CHO for PKK 5203
12/51
Glucose with 6CD- glucose chiral carbon n=4
D-glucose with 24=16 stereoisomers.
(comprise all possible aldohexoses)
# almost all naturally occuring sugars have
the D-configuration.
In all D-aldose the hydroxyl group is to the right
on the chiral carbon atom farthest from the most
oxidised carbon in the molecule (C no 5 in a six
carbon sugars)
-
8/7/2019 CHO for PKK 5203
13/51
-
8/7/2019 CHO for PKK 5203
14/51
Stereoisomers that are not enantiomers (mirror image
isomers) are called diastereomers.Aldopentoses;
D-ribose and L-ribose are enantiomers, as are D-
arabinose are diastereomers because they are isomers but
not mirror image.
Diastereomers that differ in the configuration at a single
asymmetric carbon atom are called epimers.
D-glucose and D-galactose are epimers because their
structures differ only in the configuration of the OH group
at carbon 4.D-mannose and D-galactose are not epimers because
their configuration differ at more than one carbon.
-
8/7/2019 CHO for PKK 5203
15/51
CHO
C
C
OH
OH
C HOH
C
H
H OHCH
2OH
H
D- l
l
D- l t
l
CHO
C
C
OH
OH
C OHH
C
H
H OHCH
2OH
H
T i t r m r r l pim r , t y
iff r i fi r ti t ly t r -
t r ( l r t).
-
8/7/2019 CHO for PKK 5203
16/51
Chiral carbon- carbon bonded to four different atoms or groups of
atoms).
Isomers are compound with the same chemical formula. Optical
isomers are alike with respect to what atoms are bonded to each
other but different in how the atom are oriented in space.
Epimers- are isomers with conformation that differ only at one
carbon atom.
Enantiomers are isomers that are mirror images.
-
8/7/2019 CHO for PKK 5203
17/51
Fischer Projections
In a Fischer projection, the sugarmolecule is oriented so that themost oxidized carbon is to the top.The stereocenter carbons arearranged so that the groups not part
of the main chain projecthorizontally toward the viewer.
The molecule is in the all eclipsedform.
CO H
CH OH
C
CH2OH
H OH
-
8/7/2019 CHO for PKK 5203
18/51
Monosaccharides are drawn in Fischer
projections with the most oxidized carbonclosest to the top. The carbons are numbered
from the top. If the the stereocenter with the
highest number has the OH to the right, the
sugar is D. If the OH is to the left, the sugar isL.
Most common sugars are in the D form.
Note: Fisher projections represent an alleclipsed conformation.
-
8/7/2019 CHO for PKK 5203
19/51
1
2
3
4
1
2
3
4
5
65
CC
O H
C
OHH
C
H OH
H
CH2OH
OH
CH2OH
CC
OOH
C OHH C
H
H OH
CH2OH
D-ril t
D-fr tt
-
8/7/2019 CHO for PKK 5203
20/51
Cyclic forms for sugars
Most simple sugars of four or more
carbons exist in the cyclic (hemiacetal orhemiketal) form.
A hydroxy group in the sugar reacts with
the carbonyl group. The new OH bearing carbon is now a
stereo center and is called an anomeric
carbon. If the OH on the ring is up the carbon is
F, if the OH is down it is E.
-
8/7/2019 CHO for PKK 5203
21/51
Formation of hemiacetals and hemiketals a) form an aldehyde b) form a ketone
-
8/7/2019 CHO for PKK 5203
22/51
Cyclic forms for sugars Fischer projections forE D glucose
C
CC OHOHC OHHC
H
H
CH2OH
H
OH
OH
C
CC OHOHC OHHC
H
H
CH2OH
H
OHH C
CC OHOHC OHHC
H
H
CH2OH
H
OH H
D-glucose E D-glucosecyclic form
O
F D-glucosecyclic form
O
-
8/7/2019 CHO for PKK 5203
23/51
Sugars with 5 C mostly exist in their cyclized form (intramolecular hemiacetal
formation):
y Since C1 becomes a chiral center,there are two new possible
stereoisomers that are named E and F.
yAnomers: Isomeric forms that differ
only in their configuration about
the hemiacetal or hemiketalcarbon atom. E,F anomers
y anomeric carbon the hemiacetal
carbon atom.
E
F
* *
-
8/7/2019 CHO for PKK 5203
24/51
Cyclic forms for sugars- Haworth
1. Draw a five- or six-membered ring
O O
pyranose form furanose form
2. Anomeric C to right ofO. Place OHup or down.
3. In D- sugars, the last C is always up.
furan (5 membered ring) Pyran (6-membered ring)
-
8/7/2019 CHO for PKK 5203
25/51
Cyclic forms for sugars- Haworth
CH2C O
OH
COH H
C OHH
CH
CH2OH
OH
O
CH2OH
OH
OH
OH
CH2
OH
D-fructoseF-D-fructofuranose
+ E isomer
Anomeric CF-OH
-
8/7/2019 CHO for PKK 5203
26/51
Cyclic forms for sugars- Haworth
CH2C O
OH
COH H
C OHH
CH
CH2OH
OH
O
CH2OH
OH
OH
OH
CH2
OH
D-fructoseF-D-fructofuranose
+ E isomer
Anomeric CF-OH
-
8/7/2019 CHO for PKK 5203
27/51
Cyclic forms for sugars- Glucose
OCH
2OH
HH
OHH
OH
OH
H O
H
HOCH2OH
HH
OH H
OH
OH
H O
HH
OCH
2
OH
HH
OH
H
OH
OH
HH
O H
E form
(alpha)
F form(beta)
arrows showelectron movement
Pyranose ring
form
-
8/7/2019 CHO for PKK 5203
28/51
The pyranose ring structure ofF-D-glucose
may be written as F-D-glucopyranose. The carbonyl carbon (C-1 in this case) is call
the anomeric carbon atom and so the E- and
F-forms rapidly interconvert via the open
chain structure, to give an equilibrium
mixture.
This proces is called mutarotation.
In the case of ketose, fructose, the anomeric
carbon atom (that carried the carbonyl
moiety) is C-2 and hence two isomers(anomers) exist which differ in their
configuration about the carbon atom, ie, the
EFdesignation refers to the configuration
about C-2 not C-1.
-
8/7/2019 CHO for PKK 5203
29/51
Cyclic forms for sugars- Ribose also exists mainly in the cyclic
form.
O
CH2OH
H
H
H
OH
H
OH
O
HCH
2OH
HH
OH
H
OH
O
H
O H
F D-ribose
F D-ribofuranose(furanose ring form)
arrows showelectron movement
-
8/7/2019 CHO for PKK 5203
30/51
Fisher configuration
The pyranose ring of six carbon sugar can
exist in either a boat and a chair configuration.
In the boat form, there is considerable steric
hindrance between the various groups
attached to the carbon atoms of the ring andhence this form is less favourable
energetically.
The chair form predominates, where all the
axial positions are occupied by hydrogen
atoms.
-
8/7/2019 CHO for PKK 5203
31/51
E D-glucose: the chair conformer
OH
H H
H
HOH
H
O
OH
OH
CH2OH
1
2
3
4
5
6
Four of the five bulky groups (OH and CH2OH on C2,3,4,5)
on the ring are in the more stable equitorial positions!
-
8/7/2019 CHO for PKK 5203
32/51
Fischer configuration
ofE and F-glucose
-
8/7/2019 CHO for PKK 5203
33/51
Equilibrium mixture
of D-glucose
-
8/7/2019 CHO for PKK 5203
34/51
Oxidation-reduction reactions
In the present of oxidizing agents, metal ions such as Cu2+, and
certain enzymes, monosaccharides readily undergo several
oxidation reactions.
Oxidation of
a) Aldehyde group yields and aldonic acid
b)Terminal CH2OH group (but not the aldehyde group)
gives a uronic acid.c) Aldehyde and CH2OH gives and aldaric acid.
The carbonyl groups in both aldonic and uronic acids can react
with an OH group in the same molecule to form a cyclic ester
known as a lactone.
Lactone are commonly found in nature.
L-ascorbic acid (vitamin E) is a lactone derivative of D-
glucuronic acid.
Sugars that can be oxidised by weak oxidizing agents such as
Benedicts reagent are called reducing sugars. The reaction
occurs only with sugars that can be revert to the open chain
form, all monosaccharides are reducing sugars.
-
8/7/2019 CHO for PKK 5203
35/51
Aldehyde oxidn aldonic acid
Oxidation of Monosaccharides
COOH
CC
OHOH
C OHH
C
H
H OHCH
2OH
H
D-gluconic acid
Term CH2OH oxidn
uronic acid
CHOCC
OHOH
C OHHC
H
H OHCOOH
H
D-glucuronic acid
-
8/7/2019 CHO for PKK 5203
36/51
Oxidation of Monosaccharides
Aldehyde + term CH2OH oxidn
aldaric acid
COOH
CC OHOHC OHHC
H
H OH
COOH
H
D-glucaric acid
-
8/7/2019 CHO for PKK 5203
37/51
Oxidation of Monosaccharides
O
CH2OH
HH
OHH
OH
OH
H OO
CH2OH
HH
OHH
OH
OH
H
OH
H
Aldoses react with Tollens reagent (Ag(NH3)2
+) to give a
lactone (cyclic ester). The silver ion plates out as a mirror.
Cu2+
+ Cu2O (red-orange)
Benedicts reagent (a blue copper ion solution) also gives a
lactone. The blue color fades as reaction occurs.
-
8/7/2019 CHO for PKK 5203
38/51
Reduction
Reduction of aldehyde and ketone groups of monosaccharide
yields the sugar alcohols (alditols).
D- Glucose D-glucitol or D-sorbitol
Sorbitol is used to prevent moisture loss in candy making,
pharmaceutical product.
-
8/7/2019 CHO for PKK 5203
39/51
Modern methods for blood glucose determination
(Glucose oxidase method)
H2O2 thus formed can be measured by several methods.
y H2O2 reacts with Fe(CN) in the presence of luminol to produce
luminescence proportional to the initial glucose concentration.
y H2O2 is first converted to water and oxygen by the enzyme peroxidase
(POD). Then, 4-aminophenazone, an oxygen acceptor, takes up the
oxygen and together with phenol forms a pink coloured chromogen which
can be measured at 515mm.
-
8/7/2019 CHO for PKK 5203
40/51
Reduction of Monosaccharides
The most important reduced sugar is deoxyribose. (In
DNA)
When the carbonyl of a sugar is reduced to analcohol, alditols are produced. The two shownabove are used to sweeten nonsugar gum.
D-sorbitol D-xylitol
CH2OH
C
C
OH
OH
C HOH
C
H
H OH
CH2OH
H
CH OH
CH2OH
CH2OH
C
C
OH
OH H
HC
C
O H
C
HH
C
H OH
OHH
CH2OH
D-deoxyribose
-
8/7/2019 CHO for PKK 5203
41/51
Isomerization
Monosaccharides undergo several types of
isomerization.
After several hours an alkaline solution of D-glucose
also contain D-mannose and D-fructose.
Isomerization involved intramolecular shift of a H
atom and relocation of a double bond. The
intermediate formed is called an enediol.
Reversible transformation of glucose to fructose is
an aldose ketose interconversion. Conversion of glucose to mannose is referred to as
an epimerization.
-
8/7/2019 CHO for PKK 5203
42/51
Isomerisation of D-glucose to form D-mannose and D-fructose
-
8/7/2019 CHO for PKK 5203
43/51
Esterification
Like all free OH group, those of carbohydrates can be
converted to esters by reactions with acids.
Phosphate and sulfate esters of carbohydrate molecules are
among the most common ones found in nature.
Sulfate esters of carbohydrates molecules are foundpredominantly in proteoglycan component of connective
tissue.
-
8/7/2019 CHO for PKK 5203
44/51
Esters of Monosaccharides The OH groups of sugars can react with
phosphoric acid to give phosphate esters.
O
H O O-
HH
OH
H
OH
OH
H H
OH
F -glucose- -phosphate
-
8/7/2019 CHO for PKK 5203
45/51
Gl id
-
8/7/2019 CHO for PKK 5203
46/51
Glycosides The anomeric OH can react with another OH on
an alcohol or sugar.W
ater is lost to form anacetal/ketal
O
H OH
H
H
OH
H
OH
OH
H
H
OH
H O H
O
H OH
H
H
OH
H
OH
OH
H
H
O H
H O
Acetal
carbon
-
8/7/2019 CHO for PKK 5203
47/51
Important monosaccharides
Glucose
Primary fuel for living cells.
Fructose
Fruit sugar.
Important member of ketose family.On a pergram basis, fructose is twice as sweet as sucrose-used in smaller
amount.
Always used as a sweetening agent in processed food product.
Galactose
Important as a precursor for variety of biomolecules ie, lactose in lactatingmammary glands, glycolipids, certain phospholipids, proteoglycan and
glycoprotein.
Synthesis of the above substances is not diminished by diet lack of galactose
or disaccharide lactose (galactose+glucose).Why? Galactose is epimer to
glucose, epimerase enzyme will interconvert the glucose to galactose.
-
8/7/2019 CHO for PKK 5203
48/51
A i S
-
8/7/2019 CHO for PKK 5203
49/51
Amino Sugars
OCH2
HH
OH
H
OH
NH3
+
H OH
H
OH
E-D- l i
OCH2
HH
OH
H
OH
NH
H OH
HOH
C OCH3N- tyl-E-D- l i
A i S 2
-
8/7/2019 CHO for PKK 5203
50/51
Amino Sugars-2
NHC
O
CH3
OR
OH
OH
OH
COO-
CH OHCH OH
CH2
OH
N- t l r i i ii li i
R=
-
8/7/2019 CHO for PKK 5203
51/51
c) Deoxysugars Monosaccharides in which an -H has replaced an OH group.
Eg, L-fucose and 2-deoxyribose. .
Fucose always found in glycoprotein and 2-deoxyribose in
DNA.