Biological molecules

Biological molecules

1. Water

   • Vital to living organisms
     • Reactant in many important chemical reactions,
     • Solvent as most reactions happen in solution
     • Transports substances
     • Carries away energy when evaporating so it helps cools things down
   • Simple structure
     • Polar molecule: One delta -ve oxygen and two delta +ve hydrogens
   • Properties
     • Hydrogen bonds give a high specific heat capacity
       • A lot of energy to raise the temp by 1degree
     • Hydrogen bonds give a high latent heat of evaporation
     • Polarity makes it cohesive
     • Polarity makes it a good solvent

2. Proteins

   • Made from long chains called polypeptides. A protein is made up of one or more polypeptide chains
   • They all have the same structure: carboxyl group (-COOH), an amino group (-NH2) and a carbon atom and a variable group
   • Peptide bonds: A water molecule is released during the reaction and the reverse adds a molecule of water to break the peptide bond
   • Structural levels and bonds
     • Primary: Sequence of amino acids. (Peptide bonds)
     • Secondary: Alpha helix and beta sheets (hydrogen bonds)
     • Tertiary: Coiled and folded more into a 3D structure ( Ionic bonds, disulphide bridges, hydrogen bonds and hydrophobic interactions)
     • Quaternary: Multiple polypeptide chains join together (all the bonds in tertiary)
   • Collagen is a fibrous protein. Supportive tissues in animals and is strong. Three polypeptides, tightly coiled. Interlinked by covalent bonds
     • 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

3. Carbohydrates

   • Carbohydrates are made from monosaccharides either beta or alpha.
     • 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
   • Glycosidic bonds
     • Water is released and to break the bonds add water
   • 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
     • Glycogen (main energy storage in animals). Branched, alpha glucose, good for quick release of energy. Also very compact and insoluble. 1-6 glycosidic bonds
       • 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

4. Lipids

   • Trigylcerides
     • One glycerol molecule, three fatty acids (hydrophobic) and three ester bonds. Insoluble
     • 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
   • Phospholipids
     • One glycerol molecule, two fatty acids (hydrophobic), one phosphate group (hydrophilic)
     • Make up the bilayer in cell membranes, controls what enters and leaves
   • Cholesterol
     • Hydrocarbon rings, hydrocarbon tail and a hydroxyl group makes it soluble.
     • Strengthens the cell membrane by making is less fluid and more rigid. Make them packed closer together

5. Tests for molecules

   • Benedicts test for sugars
     • Reducing sugars: Add benedicts test and heat. From blue to brick red
       • Non reducing sugars: Boil with dilute HCl and neutralise with NaHCO3, then do benedicts test
   • Iodine test for starch, from brown/orange to blue/black
   • Biurets for proteins
     • Add sodium hydroxide, then copper sulfate. From blue to purple
   • Emulsion for lipids: Shake with ethanol and then pour into water. White emulsion ontop