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CHEMISTRY OF CARBOHYDRATE & INTRODUCTORY
GLYCOBIOLOGY
OUTLINE
➢ Introduction and classification of carbohydrates
➢ Monosaccharides : properties, types and biological derivatives
➢ Oligosaccharides: types, structures and their biological use
➢ Polysaccharide: classification, types, structures, and biological functions
➢ Glycoconjugates and introductory Glycobiology
➢ Glycobiology of blood determinants
➢ Chemistry & methods of carbohydrate analysis

Carbohydrates are very important biomolecules in all living cells; they are important cell fuel,
they form protective structures, adhesive structures and biosignals, thus they are of great
interest to the biochemist
Carbohydrates are polyhydroxy aldehydes and ketones, or substances that yeild these on
hydrolysis
...
Monosaccharides
2
...
polysaccharides
Monosaccharides
Monosaccharides are aldehydes or ketone derivatives of straight chain polyhydroxy alcohols
containing at least 3 carbon atoms
...
Funtional group on first carbon; i
...
Number of carbon atoms on the monosaccharide, using nomenclatures that describe the
number of carbon, e
...

Combining this two criteria, it is explanatory that glyceraldehyde is an aldotriose ,
dihydroxyacetone is a ketotriose, glucose is an aldohexose, fructose is a ketohexose
...

Glyceraldehyde is the standard of naming optical stereoisomer, placing attention on the
configuration of the most distant chiral carbon from the carbonyl group
...
Monosaccharides are
said to either be dextrorotatory(+) or levorotatory(-) bases on manner of light rotation
to the right or left respectively
➢ EPIMERISM : this is the ability of a monosaccharides to differ in configuration around
a single carbon atom (but not the

carbonyl carbon or the carbon that confer

stereoisomerism)
...
For example, mannose is an
epimer of glucose at C2, while galactose is an epimer of glucose at C4
...
This is because this functional
interconversion occur easily through the enediol intermediate
...
Also
in the cyclic structure formed, the carbonyl carbon becomes either the hemi- acetal or
hemi-ketal carbon
➢ ANOMERISM: these are isomeric form of monosaccharides that differ only in
configurarion about hemi-acetal/ketal carbon

➢ MUTAROTATION: this is the observed change in optical rotation when anomeric
forms of monosaccharides are allowed to stand in solution
...
Monsaccharides are easily oxidized by mild oxidizing
agents such as Cu2+ in alkaline solution which thus convert them to mixtures of
carboxylic acids

BIOLOGICALLY IMPORTANT DERIVATIVE OF MONOSACCHARIDE
(GLUCOSE)
These are important monosaccharides (especially of glucose) derivative in which the –OH group
of parent skeleton is either substituted or modified
...


Oxidation

of

terminal

alcohol

group

to

COOH

produces

URONIC

ACID


...
These polyols are intermediates of metabolic
reactions
...
The alcohols formed from glucose,
galactose and fructose are sorbitol, galactitol and sorbitol, respectively
➢ Deoxy-sugars
The substitution of a hydrogen for the hydroxyl group at C6 of galactose or mannose produces
fucose or rhamnose, respectively; these deoxy sugars are found in plant polysaccharides and in

the complex oligosaccharide components of glycoproteins and glycolipids
...

➢ Sugar phosphates
these are important metabolic intermediates of carbohydrates
...
Phosphorylation
helps to trap sugar within the cell and activate it for metabolism
➢ Amino sugars: Sugars containing an –NH2 group in their structure are called amino
sugars
...
g ribosylamine
Glycosamine: In this type, the alcoholic – OH group of the sugar molecule is replaced by – NH2
group
...

Amino sugars are components of mucopolysaccharides, and antibiotics
...
N-Acetylneuraminic acid and its derivatives are often
referred to as sialic acids
...


➢ Glycosides:
Glycosides are compounds containing a carbohydrate and a non-carbohydrate residue in the
same molecule(usually O- linked or N-linked)
...
The non-carbohydrate
residue present in the glycoside is called as Aglycone
...
t
...
Glycosides are often found in
plants, and some synthetic drugs
➢ Lactones: these are stable intramolecular ester derivative of aldonic or uronic acids
...
The said monosaccharide units are joined together by glycosidic linkages
...
They consist of two
monosaccharide units linked together by oligosidic bonds
...
Maltose is a
reducing sugar
...
The anomeric carbon of the glucose residue is available for oxidation, and thus
lactose is a reducing disaccharide
...
It is formed by plants
but not by animals
...
Sucrose is therefore a nonreducing sugar
...
5°
...
8°
...

The hydrolysis mixture containing glucose and fructose is called as invert sugar
...


Other disaccharide of bilogical importance are:
•

Isomaltose: contains two glucose units in α(1→6) linkage, seen in glycogen and
amylopectin

•

Trehalose: It also contains two glucose units
...
So, it is a
non-reducing disaccharide
...
In fungi it serve as
reserve food material

•

Cellobiose: It also contains two glucose units but they are joined in β(1→4) linkage
...


Other oligosaccharides are also seen covalently attached to integral membrane proteins on
their extracellular faces
...
They are
found linked to O-side chain of serine or threonine by O-oligosidic linkage, or to the side
chain N- of asparagine via N-oligisidic linkage
...
Polysaccharides occur richly in
plants and animals, often found in their richly hydrated state , due to multiple –OH group
Polysaccharides are classified based on the types of monosaccharide present, and are
classified into two :
1
...
Heteropolysaccharide
...
HOMOPOLYSACCHARIDES: they are polymer of only one monosaccharide specie,
and yield only this monosaccharide on hydrolysis
...
Common examples are
➢ Starch: this is the polymeric form in which plant store glucose
...


Amylopectin: this has the normal linear α(1→4) of amylose, but in addition to this,
amylopectin linear structure has α(1→6) branch at every 24-30 residue
...
As

amylopectin, it also retain the linear α(1→4) chain and α(1→6) branches
...

Also, α(1→4) glycosidic bonds in starch and glycogen has a stable left-handed helix three
dimensional structure; with each link glycosidic bond constituting a 60° turn
...
This polysaccharide is common in bacteria and
yeasts
...
Cellulose like amylose is linear and
unbranched but having β(1→4) oligosidic linkage

Cellulose most stable structure is linear as each of its β(1→4) link has a turn of 180°, thus
cellulose is a straight conformed polymer, with its –OH available and arranged side by side ;
such that H-bond is maximized between adjacent strand
...
g xylem tissue
➢ Chitin: a linear homopolysaccharide composed of N-acetylglucosamine residues in
β(1→4) linkage
...
Chitin is an important component in
arthropod exoskeleton
...
HETEROPOLYSACCHARIDES: they are also known as glycosaminoglycan, composed
of repeating disaccharide unit; with one of the monosaccharide always being a Nacetylglucosamine or N-acetylgalactosamine(substituted at C2) and the other
monosaccharide unit always a uronic acid; D-glucuronic acid or its eipmer at C5; Linduronic acid
...
In multicellular
organisms, they are present in ECM fluids comprising of interlocking meshwork of
heteropolysaccharide and fibrous proteins of fibroblast and epithelial cells, they are also
found in connective tissues and mucous secretion
...


Glycosaminoglycans (GAG) often have dense negative charge due to COO- and OSO3groups
...

Hyaluronic acid function as a lubricant in synovial fluid, it gives the vitreous humor glassy
translucent appearance, it contribute tensile strength and elasticity to connective tissues as
collagen and elastin, helps also in aggregation of tissue repairing cells
...

Chondroitin sulphate help in contributing tensile strenght to connective tissues as
cartilage, tendon, ligament, they are also seen in the cornea and retina of the eye

➢ Dermatan sulphate: this GAG is structurally and functionally similar to chondroitin
sulphate, main different being that it replaces glucuronic acid with induronic(glucuronic
acid epimer atC5) acid in its make up
➢ Heparin: the repeating disaccharide of heparin consist of D-glucosamine and either Linduronic acid or glucuronic acid
...
Heparin has an all α(1→4) glysosidic linkage
...
Heparin
is the only GAG found intracellularly
➢ Keratan sulphate: this GAG is unique in that it contains no uronic acid, its disaccharide
repeat is composed of galactose and N-acetylglucasamine-6-sulphate, with intradisaccharide link of β(1→4) oligosidic bond and inter-disaccharide link of β(1→3)
...
g horn, claw, nail

➢ Bacterial and agal cells usually contain cettain structural heteropolysaccharides which
them prevent osmotic lysis
...
This linear polysaccharide lies side by
side and are cross linked by short sheet of peptide into sheet of peptidoglycan
surrounding the cell
...

Some oligosaccharides also bound to the plasma memb

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