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Key words
Carbohydrate- definition
Aldose, ketose
Classification
Enantiomer, Diastreomer, Epimer
Fischer projection, Haworth projection
CARBOHYDRATE
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Carbohydrates
Carbohydrate: most abundant biomolecules(other biomolecules protein, lipid, nucleic
acid) Suffixose indicates the molecule is a
carbohydrate
- glucose, fructose, maltose, sucrose, cellulose
Major role in energy metabolism and structuralcomponent
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Why Carbohydrates?
Play a number of important roles in
biochemistry:
Major energy sources
Play a key role of processes that take place on
the surfaces of cells. eg. cell-cell interactions
Essential structural components of severalclasses organisms.
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Carbohydrates
Definition: a polyhydroxyaldehyde or
polyhydroxyketone, or a substance thatgives these compounds on hydrolysis
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Carbohydrate
Three level number of sugar/saccharide unit
1. Monosaccharide simplest
2. Oligosaccharide consist more than 1monosaccharide > disaccharide has 2monosaccharide
3. Polysaccharide has large number ofmonosaccharide
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CARBOHYDRATE
MONOSACCHARIDE
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Monosaccharide: simplest carbohydrate,
sometimes referred as sugar / saccharide
Building blocks of all carbohydratesThey have the general formula CnH2nOn, where n
varies from 3 to 8
Aldose: a monosaccharide containing an aldehydegroup
Ketose: a monosaccharide containing a ketone group
Monosaccharides
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Monosaccharides are classified by theirnumber of carbon atoms
- 3 C = triose- 4 C = tetrose
- 5 C = pentose
- 6 C = hexose
- 7 C = heptose
Trioses are simplest carbohydrate
monosaccharides
Monosaccharides
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Aldose: containing an aldehyde group
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Ketose: containing a ketone group
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D-Glucose
This is a Fischer
Formula
6C monomeric
molecule
Is an aldohexose
D to denote theOH
on C5 is on the right
side of the C chain
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Fischer Projections and
Haworth Projections
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Fischer Projections
Fischer projection:bonds
are written in a two
dimensional representation
showing the configurationof tetrahedral stereocenters
horizontal lines represent
bonds projecting forward
vertical lines represent bondsprojecting to the rear
the carbon atom at the
intersection of the horizontal
and vertical lines is not
shown
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Comparison of the Fischer andHaworth Representations
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Glyceraldehyde contains a stereocenter andexists as a pair of enantiomers
Mirror-images stereoisomers are calledenantiomers
Monosaccharides
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Stereochemistry of monosacharides
Anomers :- (carbonyl becomes a new
chiral; C1)
Epimers :- ( excluding the anomeric
carbon )
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Enantiomers :- Molecules that are
superimposible mirror images of one
another.
Isomers : Isomers are molecules with the
same molecular formula, but differentarrangements of atoms.
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Stereoisomers : molecules that differ fromeach other only in their configuration ( three
dimensional shapes )also called optical
isomers. Glucose n Galactose.
Diastereomers :non superimposable,non mirror
image stereoisomers. ( L- Threose with both Dn L erythrose. )
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Stereoisomer
Stereoisomer that are
nonsuperimposable
mirror images of eachother = enantiomer
Chiral carbon/centre =
carbon atom connected to 4different groups
Chiral carbon
Chiral molecule
mirror
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StereoisomerD,L Monosaccharides
What is D and L?
D = dextrorotary, L = levorotary
Are stereoisomers, due to the rotated direction
of plane polarized light of solution
Enantiomers: stereoisomers that are mirror
images
example: D-erythrose and L-erythrose are
enantiomers
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D,L Monosaccharides-Fischer Projections
According to the conventions
proposed by Fischer
D-monosaccharide: a
monosaccharide that, when
written as a Fischer projection,
has the -OH on its penultimate
carbon on the right
L-monosaccharide: a
monosaccharide that, when
written as a Fischer projection,
has the -OH on its penultimate
carbon on the left
REMEMBER: D,L= enantiomers
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D,L Monosaccharides-Fischer Projections
According to theconventions proposed
by FischerD-monosaccharide:has the -OH on itspenultimatecarbon on
the rightL-monosaccharide:
has the -OH on itspenultimatecarbon on
the left
REMEMBER: D,L= enantiomers
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Diastereomers
Diastereomers: stereoisomers that are notmirror
images, non-superimposableexample: D-erythrose and D-threose are diastereomers
Epimers-diastereomer differ at only one chiral carbon
Th ld h hi l C C
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Fig. 16-3, p.437
The aldotetroses have two chiral C ; C-
2 and C-3.
Therefore, the stereoisomers of
aldotetroses are 22, or four possible
stereoisomers.
Diastereoisomers that differ from
each other at only one chiral C are
known as epimers.
D-erythrose and D-threose are
epimers.
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Diastereomers - example
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D-mannose and D-galactose differ
stereochemically from D-glucose at only 1 chiral
center D-mannose and D-galactose areEPIMERS of glucose
D-galactose is a C-4
Epimer of D-glucose
D-mannose is a C-2
Epimer of D-glucose
Epimers - example
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Fructose
Epimers of D-fructose
Enantiomers of D-fructose
Diastrereomer of D-fructose
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Fructose
Which structure represents D-Fructose?
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Lesson outcome
Draw from Fischer to Haworth
Reaction of monosaccharide
Members of disaccharide
Disaccharide formation
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What Happens if a Sugar
Forms a Cyclic Molecule?
Cyclization of sugars takes place due to interactionbetween functional groups on distant carbons, C1 to C5,to make a cyclic hemiacetal - aldose
Cyclization using C2 to C5 results in hemiketalformation.- ketose
In both cases, the carbonyl carbon is new chiral center
and becomes an anomeric carbon
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Formation of a Cyclic
Hemiacetal
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Cyclic Structure
via Haworth Projections Monosaccharides have -OH and C=O
groups in the same molecule and exist
almost entirely as five- and six-memberedcyclic hemiacetals
anomeric carbon: the new stereocenter
resulting from cyclic hemiacetal formationanomers:carbohydrates that differ in
configuration only at their anomeric carbons
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Haworth Projections
Haworth projections
five- and six-membered hemiacetals are represented as
planar pentagons or hexagons, as the case may be,
viewed through the edge
most commonly written with the anomeric carbon on
the right and the hemiacetal oxygen to the back right
the designation -means that -OH on the anomeric
carbon is cis to the terminal -CH2OH; - means that it
is trans
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Haworth Projections
A six-membered hemiacetal ring is shown by
the infix -pyran- (pyranose)
A five-membered hemiacetal ring is shown bythe infix -furan- (furanose)
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CONVERTING A FISCHER PROJECTION TO A HAWORTH
CHO
OH
HO
OH
OH
CH2OH
This -OH
determines
D- or L-
These groups
are down in
the Haworth
These groups
are up in
the Haworth
UP DOWN
This group, whichis carbon 6, will be
up in the Haworth if
D- and down if L-
Carbon 1 will be the
anomeric carbon
CH2OH
OH
OH
OH
OHO
1
23
4
5
6D -
This is the
-anomer because
the anomeric OH is
cisto -CH2OH
down
up
down
cis
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Reaction of Monosaccharides
1. Oxidation-reduction
i. Oxidation of aldoses to acid
ii. Reduction of ribose to deoxyribose
iii. Reduction of L-galactose to L-fucose (L-6deoxygalactose)
iv. Reduction of carbonyl group to hydroxyl groupformingsugar alcohol/alditols
2. Esterification
i. Formation of phosphate esters-intermediate in energymetabolism
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Oxidation
Reducing sugar: a sugar that has a
free carbonyl group (anomeric
carbon) one that can reduces an
oxidizing agent
Tollens reagent oxidizing agent
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Reduction
ribose to deoxyriboseReduction to sugar alcohol/alditols
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Esterification -
Phosphoric Esters Phosphoric esters are particularly important in themetabolism of sugars to provide energy
phosphoric esters are frequently formed by transfer of a
phosphate group from ATP
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Monosaccharide derivatives
Amino sugars
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The most abundance monosaccharide in nature.
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CARBOHYDRATE
DISACCHARIDE
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Glycosidic Bond Formation
Glycosidic bond: form between the hemiacetal ofmonosaccharide (saccharide) and the hydroxyl group of
organic compound such as alcohol.
A substance containing a glycosidic bond is a glycoside
Disaccharide: glycosidic bond formation between thehemiacetal of monosaccharide and hydroxyl group from
another hemiacetal
Glycosidic bond
due to dehydration/condensation
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Glycosidic Bond Formation
Type of bond: O-glycosidic bond
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Two Different Disaccharides of
-D-Glucose
Glycosidic linkagescan take variousforms; the anomeric
carbon of one sugar toany of the -OH groupsof another sugar toform an - or -
glycosidic linkage
Type of bond: O-glycosidic bond
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Disaccharides Sucrose
Table sugar; obtained from the juice of sugar cane and sugar beet
One unit of D-glucose and one unit of D-fructose joined by an -1,2-glycosidic bond
LactoseMade up of D-galactose and one unit of D-glucose joined by a -1,4-glycosidic bond
Galactose is a C-4 epimer of glucose
Maltose
Two units of D-glucose joined by an -1,4-glycosidic bond
Formed from the hydrolysis of starch
Cellobiose
Two units of D-glucose joined by an -1,4-glycosidic bond
Formed from the hydrolysis of cellulose
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Reducing & Non Reducing Sugar
Sugars exist in solution as an equilibrium mixture of open-
chain and closed-ring (or cyclic) structures.
In the open-chain form, the carbon atom that contains theC=O bond is called the carbonyl carbon.
Sugars that can be oxidised by mild oxidising agents such
as Benedict's Solution, Fehling's Solution,and Tollen's
Reagen are called reducing sugars because the oxidisingagent is reduced in the reaction.
Reducing sugar: one that has a free aldehyde group and
this aldehyde is easily oxidized.
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+ Ag (NH3)2Beingreduced
Tollens agent
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Haworth Projections
Anomeric
carbon
IfOH is free at theanomeric carbon =the monosaccharideis reducing sugar
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Sucrose
Anomeric carbons of glucose carbon C1 in configuration is linked to the anomeric carbon offructose C2 in configuration
anomeric carbon is tied into aglycosidic bond and none of it
able to form an open chain
containing free aldehyde and
ketone sucrose is NOT a
reducing sugar
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Lactose
Galactose in a (1-4) linkage with glucose
Principal sugar present in milk
Galactose is converted by the body to glucose and glucose usedfor energy
Reducing sugar?
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Maltose
Products from hydrolyticbreakdown of starch
Can be easily digested
by humans because ofthe presence of enzymescatalyzes the hydrolysisof (1-4) glycosidic
bonds
Reducing sugar?
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Cellobiose
Cellobiose hydrolysis product of cellulose
major component of plants
Differs from maltose at glycosidic bond
Humans do not have the capacity to
digest cellobiose or cellulose lack
the enzyme cellulase that break (1-4)
glycosidic linkages between glucose
monomers
Ruminants animals can have
bacteria in the rumen in gastrointestine
tract and secrete cellulase
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N-glycosidic bond
The -NH group of amine
substitute for hydroxyl groups
and react at the anomeric
carbon center of
carbohydrates.
New linkage is called N-
glycosidic bond Importance in the construction
ATP and in nucleic acids RNA
and DNA
ATP
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Disaccharides
Formation of glycosidic bondcondensation (-H2
O)
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CARBOHYDRATE
POLYSACCHARIDE
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Key words
Definition
Function
Homopolysaccharide andheteropolysaccharide
Cellulose, Chitin, Pectin, Peptidoglycan
Starch, glycogen
Glycoaminoglycan, glycoprotein
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Polysaccharides
Polysaccharide- When many monosaccharides
are linked together
Divided into 2type of monosaccharide orfunction
Two main function: energy storage and structure
Type of monosaccharidehomopolysaccharideand heteropolysaccharide
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Structural Polysaccharides
Cellulose
PectinChitincomponent of the exoskeleton
of invertebrates and in cell walls of
algae, fungi and yeast
Plant cell wall
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Cellulose
the major structural component of plants,
especially wood and plant fibers
a linear / unbranched polymer of approximately 2800-D-glucose units joined by
extensive intra- and intermolecular hydrogen bonding
between chains-strength
Cellobiose is the repeating
hydrolysis by cellulase
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Cellulose
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Cellulose
Cellulose is a
Structural
polysaccharide
Polymeric Structure of Cellulose
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Polymeric Structure of Cellulose
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Pectin
Important component of
plant cell walls
MonomerD-Galacturonicacid, derivative of galactose
Commercially important-
food processing industry- as gelling agent in jams
and jellies
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Chitin
the major structural component of the
exoskeletons of invertebrates and crustaceans; and
in cell walls of algae, fungi, and yeasts -1,4-glycosidic bondssimilar with cellulose
linear polymer, each chain held together by
hydrogen bonds
composed of units ofN-acetyl--D-
glucosaminediffer with cellulose
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Chitin
Differ with glucose
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Peptidoglycan
Bacterial cell walls:
prokaryotic cell
walls are constructedon the framework of
the repeating unit
NAM-NAG joined
by Presence ofpeptide
bond
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Storage Polysaccharides
Starch
Glycogen
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Starch
Starch is used for energy storage in plants
amylose: continuous, unbranched chains of up to 4000 -D-glucose units joined by
amylopectin: a highly branched polymer consisting of 24-30 unitsofD-glucose joined by and branches created by
amylases catalyze hydrolysis of-1,4-glycosidic bonds
*-amylase is an exoglycosidase and cleaves from the nonreducingend of the polymer
*-amylase is an endoglycosidase and hydrolyzes glycosidiclinkages anywhere along the chain to produce glucose and maltose
debranching enzymes catalyze the hydrolysis of-1,6-glycosidicbonds
Starch
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Starch
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Amylose and Amylopectin
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Amyloseoccurs as a helixwith 6 residues per turn- able to give the dark-blue colorcomplex with iodine.
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Glycogen
Glycogen is used for energy storage in animals
Has amylose and amylopectinsimilar to starch
Differ with starchthe amylopectin is highly branched
- branch point: occur about every 10 residues
in starch, about
every 25 residues
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Polysaccharides
Homopolysaccharide: consists of one type of
monosaccharide
Heteropolysaccharide: consists of more than
one type of monosaccharide
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Polysaccharides
H t l h id
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Heteropolysaccharide:
Glycosaminoglycans
Glycosaminoglycans: polysaccharides based on a
repeating disaccharide where one of the monomers
is an amino sugar and the other has a negative
charge due to a sulfate or carboxylate group
Heparin: natural anticoagulant
Hyaluronic acid: a component of the vitreous humor
of the eye and the lubricating fluid of joints Chondroitin sulfate and keratan sulfate: components
of connective tissue
H t l h id
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Heteropolysaccharide:
Glycosaminoglycans
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Glycoproteins
Glycoproteins contain carbohydrate units covalentlybonded to a polypeptide chain
antibodies are glycoproteins
Oligosaccharide portion of glycoproteins act as antigenicdeterminants
Among the first antigenic determinants discovered were the bloodgroup substances
In the ABO system, individuals are classified according to fourblood types: A, B, AB, and O
At the cellular level, the biochemical basis for this classification isa group of relatively small membrane-bound carbohydrates
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QUIZ
1. Give two important functions of polysaccharide.
2. Name 2 structural polysaccharide and 2 storagepolysaccharide.
3. Give one example of heteropolysaccharide.