Biological molecules

Water
1. Vital to living organisms
  1. Reactant in many important chemical reactions,
  2. Solvent as most reactions happen in solution
  3. Transports substances
  4. Carries away energy when evaporating so it helps cools things down
2. Simple structure
  1. Polar molecule: One delta -ve oxygen and two delta +ve hydrogens
3. Properties
  1. Hydrogen bonds give a high specific heat capacity
    1. A lot of energy to raise the temp by 1degree
  2. Hydrogen bonds give a high latent heat of evaporation
  3. Polarity makes it cohesive
  4. Polarity makes it a good solvent
Proteins
1. Made from long chains called polypeptides. A protein is made up of one or more polypeptide chains
2. They all have the same structure: carboxyl group (-COOH), an amino group (-NH2) and a carbon atom and a variable group
3. Peptide bonds: A water molecule is released during the reaction and the reverse adds a molecule of water to break the peptide bond
4. Structural levels and bonds
  1. Primary: Sequence of amino acids. (Peptide bonds)
  2. Secondary: Alpha helix and beta sheets (hydrogen bonds)
  3. Tertiary: Coiled and folded more into a 3D structure ( Ionic bonds, disulphide bridges, hydrogen bonds and hydrophobic interactions)
  4. Quaternary: Multiple polypeptide chains join together (all the bonds in tertiary)
5. Collagen is a fibrous protein. Supportive tissues in animals and is strong. Three polypeptides, tightly coiled. Interlinked by covalent bonds
  1. Haemoglobin is a globular protein. Iron containing haem group. Hydrophilic side chains and hydrophobic side chains face inwards. Soluble in water so its good for transport
Carbohydrates
1. Carbohydrates are made from monosaccharides either beta or alpha.
  1. They are soluble so it can be transported as it is the main energy source in plants and animals. Chemical bonds contain a lot of energy
2. Glycosidic bonds
  1. Water is released and to break the bonds add water
3. Starch (main energy storage in plants). Amylose is long, unbranched alpha glucose. Coiled so it can fit into small places. Starch is insoluble so it is good for storage. 1-4 glycosidic bonds
  1. Glycogen (main energy storage in animals). Branched, alpha glucose, good for quick release of energy. Also very compact and insoluble. 1-6 glycosidic bonds
    1. Cellulose (major component in cell walls in plants). Made from long, unbranched, beta glucose. Bonds are straight. Cellulose chains are linked by hydrogen bonds. Provide structural support. 1-4 gylcosidic bonds
Lipids
1. Trigylcerides
  1. One glycerol molecule, three fatty acids (hydrophobic) and three ester bonds. Insoluble
  2. Hydrocarbon tails contain lots of chemical energy so they are insoluble. Don't allow water in as it would swell. Triglycerides bundle together, fatty acid tails inside, as a storage molecule
2. Phospholipids
  1. One glycerol molecule, two fatty acids (hydrophobic), one phosphate group (hydrophilic)
  2. Make up the bilayer in cell membranes, controls what enters and leaves
3. Cholesterol
  1. Hydrocarbon rings, hydrocarbon tail and a hydroxyl group makes it soluble.
  2. Strengthens the cell membrane by making is less fluid and more rigid. Make them packed closer together
Tests for molecules
1. Benedicts test for sugars
  1. Reducing sugars: Add benedicts test and heat. From blue to brick red
    1. Non reducing sugars: Boil with dilute HCl and neutralise with NaHCO3, then do benedicts test
2. Iodine test for starch, from brown/orange to blue/black
3. Biurets for proteins
  1. Add sodium hydroxide, then copper sulfate. From blue to purple
4. Emulsion for lipids: Shake with ethanol and then pour into water. White emulsion ontop

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Biological molecules

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