Polysaccharides

Polysaccharides

1. Starch

   • The main energy storage material in plants
   • Cells get energy from glucose
     • Plants store excess glucose as starch
       • When a plant needs more glucose for energy it breaks down starch to release the glucose
   • Starch is a mixture of two polysaccharides of alpha-glucose
     • Amylose
       • A long, unbranched chain of alpha-glucose
       • The angles of the glycosidic bonds give it a coiled structure
         • This makes it compact
           • Good for storage because you can fit more into a small space
     • Amylopectin
       • A long, branched chain of alpha glucose
       • Its side branches allow enzymes that break down the molecule to get at the glycosidic bonds easily
         • This means glucose can be released quickly
   • Starch is insoluble in water, so it doesn't cause water to enter the cell by osmosis
     • Will cause them to swell
     • This makes it good for storage

2. Glycogen

   • The main energy storage material in animals
   • Animals cells get energy from glucose
     • Animals store excess glucose as glycogen
       • A polysaccharide of alpha-glucose
   • Structure is similar to amylopectin
     • Glycogen has more side branches
       • Stored glucose can be released quickly
         • Important for energy release in animals
   • Very compact molecule
     • Good for storage

3. Cellulose

   • The major component of cell walls in plants
   • Long, unbranched chains of beta-glucose
   • The bonds between sugars are straight
     • Cellulose chains are straight
   • Cellulose chains linked together by hydrogen bonds to form strong fibres called microfibrils
     • Strong fibres mean cellulose provides structural support for cells