Biology 1.3 Food and health.

Mono-saccharides
1. General Formula: (CH2O)n
2. Classified according to the number of carbon atoms
  1. 3- Triose
  2. 5- Pentose
  3. 6 - Hexose
3. Sweet
Di-saccharides
1. General Formula (C6H1O5)n
2. 2 mono-saccharides
3. Sweet
4. Examples: Sucrose, Lactose and Maltose
5. Joined by a condensation reaction resulting in glycosidic bonds(covalent)
  1. Condensation reaction: two mono-saccharides join together and water molecule is removed
    1. 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.
Poly-saccharides
1. Long chains of mono-saccharides
2. repeated condensation reactions.
3. normally 1000's of monomers
4. Complex carbohydrates
5. Not sweet
6. Poly-saccharides are polymers formed by glycosidic bonding of mono-saccharide subunits.
7. Important poly-saccharides
  1. Starch
    1. Mixture of 2 poly-saccharides - amylose and amylopectin
    2. Forms solid grains inside plant cells (often inside chloroplasts)
    3. The branches in amylopectin are formed by other 1-4 linked chains joing the main poly-saccharide by 1-6 linkages.
    4. Used as an energy store in plants
    5. Not soluble
    6. Amylopectin is branched, amylose is not.
    7. 1-4 linked (linked between carbon atoms 1 and 4 successive glucose units) glucose molecule make up the chains of both poly-saccharides
    8. The chains coil up into a basic spiral shape making the molecules compact
    9. Hydrogen bonds hold the poly-saccharide chain in the compact shape.
    10. Made of alpha glucose molecules linked by glycosidic bonds.
  2. Cellulose
    1. Constitutes on average 20-40% of the plant cell wall.
    2. Made of beta glucose units.
    3. Most abundant organic molecule - found in plant cell walls. It is very slow to decompose.
    4. Enzyme cellulase can break down cellulose, but it is relatively rare in nature.
    5. The chains straight, not coiled.
    6. Hydrogen bonding between mono-saccharide molecules in the chain gives strength
    7. Hydrogen bonding between cellulose molecules cause bundles called microfibrils to develop. These are held together in fibres
    8. A cell wall will have several layers of fibres running in different directions - gives great strength almost equal to steel.
    9. Provides support in plants and stops plant cells bursting.
    10. Freely permeable to water and solutes
    11. Ruminants have bacteria in the gut that are capable of breaking down cellulose
  3. Glycogen
    1. This is the storage poly-saccharide in animals (equivalent to starch in plants)
    2. Found in the liver and muscle cells where a energy store is needed.
    3. Mainly fungi also store glycogen
    4. Forms tiny granules inside cells which are usually associated with smooth endoplasmic reticulum.
    5. Each glycogen molecule contains a few 1000 glucose units.
    6. Similar in structure to amylopectin- but more branched i.e made of 1-4 linked alpha glucose chains with 1-6 linked side branches.
  4. Chitin
    1. Beta glucose 1-4 polymer.
    2. Subunits: derivatives of beta-glucose called N-acetylglucosamine.
    3. Abundant structural molecule in arthropod exoskeletons and fungal cell walls.

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Biology 1.3 Food and health.

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