Please enable JavaScript.
Coggle requires JavaScript to display documents.
Carbohydrates and Glycobiology, Heparin and Heparan Sulfate, Extracellular…
Carbohydrates and Glycobiology
Carbohydrates
functions
energy source and energy storage
structural component of cell walls and exoskeletons
informational molecules in cell-cell signaling
rang
glyceraldehyde (Mw = 90 g/mol)~ amylopectin (Mw > 200,000,000 g/mol)
Can be covalently linked with proteins and lipids
Basic nomenclature
number of carbon atoms in the carbohydrate + -ose
Common functional groups
All carbohydrates initially had a carbonyl functional group.
aldehydes = aldose
ketones = ketose
Can Be Stereoisomers
Enantiomers
most distant from the carbonyl carbon is designated as D (right) or L (left)
Most hexoses are D stereoisomers
Some simple sugars occur in the L form
Epimers
only one chiral center
NOT enantiomers,it is Diastereomers
Diastereomers
different physical properties
Hemiacetals and Hemiketals
Aldehyde and ketone carbons are electrophilic
Alcohol oxygen atom is nucleophilic
aldehydes are attacked by alcohols, hemiacetals form
ketones are attacked by alcohols, hemiketals form
the basis of cyclization of sugars
Cyclization of Monosaccharides
the former carbonyl oxygen becomes a hydroxyl group, the position of this group determines if the anomer is α or β
hydroxyl group is on the opposite side (trans) of the ring as the CH2OH moiety, the configuration is α
the hydroxyl group is on the same side (cis) of the ring as the CH2OH moiety, the configuration is β
Pyranoses and Furanoses
Six-membered oxygen-containing rings are called pyranoses after the pyran ring structure
favor “chair” conformations
Five-membered oxygen-containing rings are called furanoses after the furan ring structure.
Reducing Sugars
have a free anomeric carbon
Aldehyde can reduce Cu2+ to Cu+ (Fehling’s test)
Aldehyde can reduce Ag+ to Ag0 (Tollens’ test)
Modern detection techniques use colorimetric and electrochemical tests
Colorimetric Glucose Analysis
The Glycosidic Bond
between an anomeric carbon and a hydroxyl carbon
The glycosidic bond(anacetal) between monomers is more stable and less reactive than the hemiacetal at the second monomer.
Disacharides can be named by the organization and linkage or a common name.
The common name for this disaccharide is maltose
Nonreducing Disaccharides
a glycosidic bond between two anomeric carbons
The product has two acetal groups and no hemiacetals.
There are no reducing ends; this is a nonreducing sugar.
Polysaccharides
homopolysaccharides (one monomer unit)
Homopolymers of Glucose
Glycogen
branched homopolysaccharide
It functions as the main storage polysaccharide in animals.
Molecular weight reaches several millions
Glucose monomers form (α1 → 4) linked chains
branch points with (α1 → 6) linkers every
8–12 residues.
Starch
Starch is a mixture of two homopolysaccharides of glucose
Amylose is an unbranched polymer of (α1 → 4) linked residues
Amylopectin is branched like glycogen, but the branch points with (α1 → 6) linkers occur every 24–30 residues.
Molecular weight of amylopectin is up to 200 million.
Starch is the main storage polysaccharide in plants
Metabolism of Glycogen and Starch
insoluble due to their high molecular weight and often form granules in cells
Granules contain enzymes that synthesize and degrade these polymers.
Glycogen and amylopectin have one reducing end but many nonreducing ends.
Enzymatic processing occurs simultaneously in many nonreducing ends.
Cellulose
Cellulose is a linear homopolysaccharide of glucose.
Glucose monomers form (β1 → 4) linked chains.
Hydrogen bonds form between adjacent monomers
tough and water insoluble
most abundant polysaccharide in nature
Cotton is nearly pure fibrous cellulose
Cellulose Metabolism
Most animals cannot use cellulose as a fuel source because they lack the enzyme to hydrolyze (β1 →4) linkages.
Fungi, bacteria, and protozoa secrete cellulase, which allows them to use wood as source of glucose.
Chitin Is a Homopolysaccharide
Chitin is a linear homopolysaccharide of N-acetylglucosamine.
N-acetylglucosamine monomers form (β1 → 4)-linked chains
forms extended fibers that are similar to those of cellulose
hard, insoluble, cannot be digested by vertebrates
structure is tough but flexible, and water insoluble
found in cell walls in mushrooms and in exoskeletons of insects, spiders, crabs, and other arthropods
heteropolysaccharides (multiple monomer units)
Agar and Agarose
Agar
growing bacteria
Agarose
separation DNA by electrophoresis.
linear (one type of glycosidic bond)
branched (multiple types of glycosidic bonds)
Glycosaminoglycans
Linear polymers of repeating disaccharide units
One monomer is either
N-acetyl-glucosamine
N-acetyl-galactosamine
Negatively charged
uronic acids (C6 oxidation)
sulfate esters
Forms meshwork with fibrous proteins to form extracellular matrix
connective tissue
lubrication of joints
Glycoconjugates
Glycoprotein
small oligosaccharides attached
Carbohydrates play role in protein-protein recognition
Viral proteins are heavily glycosylated; this helps evade the immune system
Glycolipids
Lipids with covalently bound oligosaccharide
parts of plant and animal cell membranes
In vertebrates, ganglioside carbohydrate composition determines blood groups.
In gram-negative bacteria, lipopolysaccharides cover the peptidoglycan layer
Proteoglycans
syndecans
protein has a single transmembrane domain
glypicans
protein is anchored to a lipid membrane
Heparin and Heparan Sulfate
Heparin is linear polymer
Heparan sulfate is heparin-like polysaccharide but attached to proteins.
Highest negative-charge density biomolecules
Prevent blood clotting
regulates development and formation of blood vessels.
bind to viruses and bacteria and decrease their virulence
Extracellular Matrix (ECM)
Strength, elasticity, and physical barrier in tissues
Main components
proteoglycan aggregates
collagen fibers
elastin
ECM is a barrier for tumor cells seeking to invade new tissues.
Some tumor cells secrete heparinase that degrades ECM
Interaction of the Cells with ECM
These proteins link cellular cytoskeleton to the ECM and transmit signals into the cell to regulate
cell growth
cell mobility
apoptosis
wound healing
