Summary OCR A/AS-Level Biology 2.2.4-5 Polysaccharides

Polysaccharides
Starch
 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