carbohydrates - structural Flashcards
Structural polysaccharides
4 points
- Contain mostly b-links between sugars; not readily degraded
- Polysaccharides giving structural support alternate monosaccharide units invert (flip over) to give long straight chain.
- The straight chains will align next to each other
Interactions: Hydrogen bonding between chains increases strength
- Vast majority forms cell walls => desired strength
What is the cell wall?
3 points
- polysaccharide and glycoprotein rich layer located outside the cell membrane
- Specific feature to cells of:
plants, algae
bacteria
fungi - not present in animal cells and protozoans
Main difference between cell walls
Plants
3 points
- Cellulose
- hemicelluloses
- pectins
Main difference between cell walls
fungi
3 points
- chitin
- hemicelluloses
- mannoproteins
Main difference between cell walls
bacteria
2 points
- bacteria cellulose
2. peptidoglycan
primary and secondary cell wall
- Primary cell wall
thin, flexible & extensible layer - Secondary cell wall
Lignified (full of poly-phenolics), rigid & provides strength (wood)
Cellulose
6 points
- the skeleton of plant cell walls
- Chains of b-(1-4) linked glucose =
each glucose is rotated 180°from the previous one [flipped] - Because of the straight chains, several chains align parallel to each other to form microfibrils
- Macrofibrils and fibres are arranged in random matrix / directions to give strength to plant cell walls – no shear plane
- The molecules are held together by intermolecular hydrogen bonds between –OH group and glycosidic O
- Microfibrils contain crystalline and amorphous regions
Hemicelluloses
4 points
- shorter chains than cellulose; 500–3,000 sugar units
- tether and crosslink individual cellulose microfibrils
- the amount, structure and chemical composition differs among various plants
- different but a bit like cellulose
Hemicelluloses - the basic structural similarities with cellulose
3 points
- Cellulose -> B-(1,4)-glucan; B-(1,4)-linked glucose
- Mixed linkage glucan -> B-(1,3)-(1,4)-glucan
- Xyloglucan (a heteropolymer of glucose, xylose and galactose)
[erin look up how you number carbons]
Pectins
- Complex heteropolysaccharides (chemically different residues)
; acidic macromolecules rich in galacturonic acid - Present in most primary cell walls; particularly abundant in the non-woody parts of plants
- A major component of the middle lamella, - helps to bind cells together
Plant cell-wall polysaccharides – industrial applications
Pectins
- apple, citrus
- Food industry:
gelling & thickening agent; stabilizer. Jams, Jellies
Plant cell-wall polysaccharides
– industrial applications
hemicelluloses
- Food industry:
dietary fibres, nutritional supplements
e.g. xyloglucan, xylan mixed-linkage glucan
Cellulose industrial applications
4 points
- Paper , paperboard & cellophane industry
- Textile industry industry:
the main ingredient of textiles made from cotton, linen - Pharmaceutical industry:
filler in drug tablets; anticaking agent - Biofules:
Feedstock for 2nd generation biofuels: bioethanol, gasoline, etc
Polysaccharides that involve sugar derivatives
Sugar derivative – when lost or gained some atoms / functional groups
- Amino sugars: -NH2 (amine group) replaces one of the –OH groups [on glucose] (e.g. glucosamine)
– that forms an amine - The –NH2 group of amino sugars often combines with acetic acid to form an amide (e.g. N-acetyl-glucosamine)
Chitin – structural polysaccharide
5 points
- Insect and crustaceans exoskeleton
- Same basic structure as cellulose – β(1,4) bonds; alternate units will invert so they’ll form a straight chain; they can align parallel to each other; they can form fibres
but the –OH group at C2 is replaced by N-acetyl-glucosamine (an amide)
NH
O = C - CH3
- Soft and leathery.
provides both strength and elasticity. It becomes hard when impregnated with calcium carbonate - Often seen in crustaceans
- In fungal walls, often known as ‘fungal cellulose’
Bacterial cell walls – peptidoglycan (murein)
- Chains of heteropolysaccharide made up of repeating N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM) linked by B1-4 glycosidic bonds
- a mesh like layer
- held together by tetra-peptide chains attached to NAM
Summary
Structural polysaccharides contain mostly
B-links
Summary
cell walls of plants consist of
cellulose, hemicelluloses and pectins
Summary
The fungal cell walls contain
chitin (also forms an exoskeleton of insects and crustaceans)
Summary
The bacterial cell wall contains
peptidoglycan – but has no hemicelluloses or cellulose in it
