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’
