Carbohydrates - storage Flashcards
2 types of polysaccharides based on the presence of basic sugar units (sugar residues)
- Homo-polysaccharides
=> Chemically similar residues - Hetero-polysaccharides => Chemically different units
(both can have side chains)
Storage overveiw
4 points
- Energy stores.
- a-Links (exception: fructan’s got b-links!)
- readily degraded by enzymes
- e.g. starch, fructans (plants)
glycogen (animals)
structural overview
3 points
- Provide structural integrity in plant, algal and fungal cell walls; also form a skeleton of arthropods (invertebrate animals).
- Contain b-links; not readily degraded by enzymes
3. e.g. cellulose (plants) hemicelluloses (plants, fungi) pectins (plants), peptidoglycans (bacteria), chitin (fungi, insects)
Storage polysaccharides 4 points
- Store large numbers of monosaccharide units as single polysaccharide molecules
- Important to reduce osmotic pressure within cells
- a-links are readily degraded by enzymes produced by wide range of organisms
- Highly branched molecules permit rapid release of monosaccharide
Starch 4 points
- Storage polysaccharide in plants
- Storage form of sugar deposited in starch grains of corms, bulbs, rhizomes, tubers, and seeds
- Present in starch granules of chloroplasts – ‘transitory’ starch
- Two components: amylose and amylopectin
Starch: Amylose
5 points
- A few hundred to ~2,500 glucose units arranged in an unbranched chain joined a(1-4).
- Only 1 reducing sugar end and 1 non-reducing end in whole molecule
- Because of the angle of the C-O-C glycosidic bond the chain coils to form a helix
- Two helical forms – single or double helix
- Unlike amylopectin, not soluble in cold water – but soluble in hot water
Reducing sugar:
2 points
- the monosaccharide with the free anomeric C can reform a straight chain =>
carbonyl (-C=O) group can be oxidised (-COOH). - If the sugar is oxidised it acts as a reducing agent.
Starch: Amylopectin
- A branched molecule
- Main backbone of a(1-4) linked glucose (like amylose)
- Branches connected every ~15-25 glucose units by a(1-6) bonds
- Amylopectin has 5,000 -2,000,000 glucose units per molecule
- It has one reducing end and many non-reducing ends
Starch industrial applications
6 points
- Food industry:
Thickener and stabilizer (puddings, soups, sauces..)
Bakery & beverages (beer, whisky, cola) - Pharmaceutical industry:
filler in drug tablets - Cosmetics:
Foundation make up, toothpaste, powders, creams etc. - Paper industry:
Copy paper contains ~4-8% modified starch to provide strength and smoothness - Adhesives: glues
Can swell / gelatinize - Biofuels
1st generation bioethanol
Glycogen
4 points
- Storage polysaccharide in animals
- Stored in liver and muscle
- Structure very similar to amylopectin. But it has got a 1-6 branches every 10-12 glucose units (more branches than amylopectin). The much higher
- Due to many branches, it has got very large number of non-reducing ends [more than amylopectin]
Fructans - Inulin
- Storage polysaccharide in roots and tubers of some plants, e.g. chicory and Jerusalem artichoke
- Polymer of fructose, usually with glucose at one end
- Stored in plant vacuoles
- Help to regulate osmosis and stabilise membranes during stress (drought, cold)
- Not digested in human small intestine (dietary fibre)
Fructans – industrial applications
1. Food industry: Chicory root (a coffee additive and coffee substitute
Dandelion flowers (dandelion honey)
Isolated fructans (dietary fibre)
- Oligofructans – sweeteners for reduced calorie foods, prebiotic ingredients in cereals and drinks (prebiotics beneficial as they alter the composition of organisms in the gut microbiome)
Summary
Storage polysaccharides contain ______ between sugars
a links
readily degraded by enzymes; sugars released become available to the living cells for production of energy and biosynthetic activity.
Typical plant storage polysaccharides
Starch and fructans
animal storage polysaccharides
Glycogen
stored in liver and muscles of animals more branched than amylopectin
