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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
...
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 membrane of eukaryotic cells and act
as the information rich surface of the cell to its surrounding, they function in cell
recognition and adhesion, immune response, wound healing and other cellular
processes
...

Glycoconjugates are often classified into 3:
1
...
Glycoprotein
3
...
Proteoglycans:

these

are

glycoonjugates

in

which

one

or

more

sulphated

heteropolysaccharide chain are linked covalently to serine residue of a membrane
protein

through

a

tetrasaccharide

bridge

as

illustrated

below

the serine residue at the point of attachment is often of the 1° sequence –Ser-Gly-X-Gly(from N to C terminal), where X is oftten any amino acid residue
...
g syndecans and
glypicans
...
Also, some
proteoglycan can form a “proteoglycan aggregate” which is a large supramolecular
assembly of many core protein bound to glycosaminoglycan, but all bound to a
hyalorunan backbone through a link protein, i
...


2
...
Such oligosaccharides are often small,branched,
heterogeneous and attached to the protein via its anomeric carbon atom in an Oglycosidic bond with the –OH group of serine or threonine residue, or through an Nglycosidic link between the oligosaccharide anomeric carbon and the amide nitrogen of
an asparagine residue in the protein
...
Note that the bulk –OH of
sugar moiety affects the solubility and folding and extension of glycoproteins
...
Glycolipids: these are glycoconjugates having one or more sugar head group linked
directly to the –OH group at C1 of ceramide
...

4
...
These
molecules are prime targets of the antibodies produced by the vertebrate immune
system in response to bacterial infection and are therefore important determinants of
the serotype of bacterial strains
...

structurally, lipopolysaccharides have a common a glycolipid region called lipid-A, a
core oligosaccharide similar in related bacteris, and the O-specific chain which is the
sole serotype determinant and inducer of immunological activity
...
Each glycan represents a unique three
dimensional face usually referred to as “word of sugar code”, which is readably
interpreted by the protein(lectin) that interact with it
...

Lectins are proteins that bind carbohydrate with high specificity and moderate affinity

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