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Summary OCR A/AS-Level Biology 2.2.4-5 Polysaccharides
Revision summary of key knowledge from OCR A/AS-Level Biology 2.2.4-5 Polysaccharides.
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PolysaccharidesStarch
Major energy store in plants
Stored as intercellular starch grains in organelles called plastids
Produced from α-glucose during photosynthesis
Amylase
o Straight chains coiled in a spiral shape
o Joined by 1-4 glycosidic bonds
Amylopectin
o Branched chains coiled in a spiral shape
o Main chains joined by 1-4glycosidic bonds
o Branches joined by 1-6 glycosidic bonds
As a good storage molecule
o Compact and stable from coiling
o Insoluble so it does not affect water potential or osmotic properties
o Can be easily broken down by enzymes due to many ends
Glycogen
Major energy store in animals
Stored as small granules in muscles and liver
Less dense and more soluble than starch which indicates the higher metabolic rate in
animals than plants
More branches = more ends = easier to break down
Cellulose
Main structural component in plant cell walls
Long chains of β-glucose joined by 1-4 glycosidic bonds
Chains form rope-like microfibrils which are layered to form a network
Very strong and prevents cells from bursting when taking in excessive water
Every other molecule must rotate 180º
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