Biology 1.3 Food and health.

Biology 1.3 Food and health.

1. Mono-saccharides

   • General Formula: (CH2O)n
   • Classified according to the number of carbon atoms
     • 3- Triose
     • 5- Pentose
     • 6 - Hexose
   • Sweet

2. Di-saccharides

   • General Formula (C6H1O5)n
   • 2 mono-saccharides
   • Sweet
   • Examples: Sucrose, Lactose and Maltose
   • Joined by a condensation reaction resulting in glycosidic bonds(covalent)
     • Condensation reaction: two mono-saccharides join together and water molecule is removed
       • Hydrolisis is the opposite reaction to the condensation reaction which formed the molecule, so water is added to the di-saccharide to split them apart into two mono-saccharides.

3. Poly-saccharides

   • Long chains of mono-saccharides
   • repeated condensation reactions.
   • normally 1000's of monomers
   • Complex carbohydrates
   • Not sweet
   • Poly-saccharides are polymers formed by glycosidic bonding of mono-saccharide subunits.
   • Important poly-saccharides
     • Starch
       • Mixture of 2 poly-saccharides - amylose and amylopectin
       • Forms solid grains inside plant cells (often inside chloroplasts)
       • The branches in amylopectin are formed by other 1-4 linked chains joing the main poly-saccharide by 1-6 linkages.
       • Used as an energy store in plants
       • Not soluble
       • Amylopectin is branched, amylose is not.
       • 1-4 linked (linked between carbon atoms 1 and 4 successive glucose units) glucose molecule make up the chains of both poly-saccharides
       • The chains coil up into a basic spiral shape making the molecules compact
       • Hydrogen bonds hold the poly-saccharide chain in the compact shape.
       • Made of alpha glucose molecules linked by glycosidic bonds.
     • Cellulose
       • Constitutes on average 20-40% of the plant cell wall.
       • Made of beta glucose units.
       • Most abundant organic molecule - found in plant cell walls. It is very slow to decompose.
       • Enzyme cellulase can break down cellulose, but it is relatively rare in nature.
       • The chains straight, not coiled.
       • Hydrogen bonding between mono-saccharide molecules in the chain gives strength
       • Hydrogen bonding between cellulose molecules cause bundles called microfibrils to develop. These are held together in fibres
       • A cell wall will have several layers of fibres running in different directions - gives great strength almost equal to steel.
       • Provides support in plants and stops plant cells bursting.
       • Freely permeable to water and solutes
       • Ruminants have bacteria in the gut that are capable of breaking down cellulose
     • Glycogen
       • This is the storage poly-saccharide in animals (equivalent to starch in plants)
       • Found in the liver and muscle cells where a energy store is needed.
       • Mainly fungi also store glycogen
       • Forms tiny granules inside cells which are usually associated with smooth endoplasmic reticulum.
       • Each glycogen molecule contains a few 1000 glucose units.
       • Similar in structure to amylopectin- but more branched i.e made of 1-4 linked alpha glucose chains with 1-6 linked side branches.
     • Chitin
       • Beta glucose 1-4 polymer.
       • Subunits: derivatives of beta-glucose called N-acetylglucosamine.
       • Abundant structural molecule in arthropod exoskeletons and fungal cell walls.