1.1 biological molecules

• Atom


  Smallest particle in an element that has the properties of the element
• Molecule


  Formed by the combination of two or more atoms. Unlike atoms, molecules can be subdivided to individual atoms
• Element


  Pure substance that is made out of just one kind of atom. The most common elements in living organisms are hydrogen, carbon, oxygen and nitrogen
• Compound


  Substance that is made out of two or more different elements
• Organic compound


  Has carbon-hydrogen bonds
• Inorganic compound


  Does not have carbon-hydrogen bonds
• Macronutrients - needed in small amounts

  • Magnesium
  • Iron
  • Phosphate
  • Calcium
• Micronutrients - needed in trace (tiny) amounts


  • Copper
  • Zinc
• Monosaccharide


  Monomer (made of one functional unit) e.g. glucose. Relatively small organic molecules which are joined together to make larger molecules. Named according to number of carbon atoms: three = triose, five = pentose, six = hexose. Soluble and sweet. All are reducing sugars

  
• Glucose


  Example of a monosaccharide that can exist in two forms (isomers), the α and β form, which differ in the orientation of the H and OH on carbon 1

  
• Fructose and galactose


  Also monosaccharides

  
• Disaccharide


  Formed by joining two hexose units in a condensation reaction where water is eliminated and a glycosidic bond is formed. The reverse reaction is hydrolysis
• Sucrose


  Example of a non-reducing sugar - does not give a brick-red colour with Benedict's solution unless hydrolysed with acid first
• Polysaccharide


  Large complex molecule (polymer) formed from many monosaccharide units linked together
• Types of polysaccharides


  • Storage polysaccharides (e.g. starch, glycogen)
  • Structural polysaccharides (e.g. cellulose, chitin)

  
• Starch


  Storage polysaccharide in plants, made up of amylose (linear, α 1-4 links) and amylopectin (branched, α 1-4 and α 1-6 links)

  
• Glycogen


  Storage polysaccharide in animals, has α 1-4 and α 1-6 links

  
• Starch and glycogen


  • Compact, insoluble, readily broken down into monosaccharides and disaccharides

  
• Cellulose


  Structural polysaccharide found in plant cell walls, made of long parallel chains of β-glucose molecules cross-linked by hydrogen bonds

  
• Chitin


  Structural polysaccharide forming the exoskeleton of insects, similar to cellulose but with some -OH groups replaced by nitrogen-containing acetylamine groups

  
• Testing for starch


  Add iodine/potassium iodide solution, blue-black colour indicates presence of starch
• Testing for reducing sugars (e.g. glucose)

  Add Benedict's reagent, heat, precipitate indicates reducing sugar. Colour/density indicates concentration

  
• Testing for non-reducing sugars (e.g. sucrose)

  Add hydrochloric acid, heat, neutralise, add Benedict's reagent, heat, precipitate indicates non-reducing sugar. Colour/density indicates concentration

  
• Testing for protein


  Add Biuret solution, blue ring forms at surface, solution turns lilac-purple, indicating presence of protein

  
• Testing for lipids


  Shake with ethanol, decant into water, cloudy white emulsion indicates presence of lipids
• Lipid


  Contains carbon, hydrogen and oxygen (less O than CHO) plus phosphorus as phosphate in phospholipids. Non-polar, insoluble in water but soluble in organic solvents. Main types are fats and oils depending on melting point
• Triglyceride


  Common type of lipid, consists of glycerol and fatty acids joined by condensation reactions

  
• Fatty acid


  Contains an acid (COOH) group attached to a hydrocarbon chain, usually with an even number of carbon atoms between 14 and 22

  
• Saturated fatty acid


  Every carbon atom in the chain is joined by a single C-C bond

  
• Unsaturated fatty acid


  At least one C=C double bond, therefore less H atoms

  
• Polyunsaturated fatty acid


  Many double bonds

  
• Most animal fats are saturated, most plant fats are unsaturated
• High intake of saturated fat has been linked to heart disease
• Phospholipid


  One of the fatty acids of a triglyceride is substituted by a phosphate group. The lipid part is non-polar and insoluble in water (hydrophobic), the phosphate group is polar and dissolves in water (hydrophilic). Important in cell membrane structure

  
• Protein


  Polymer of amino acids - there are 20 different types of amino acid which differ by the R group

  
• Lipids


  Yield more energy per gram on oxidation than the same mass of carbohydrate
• Lipids


  Metabolic source of water - when oxidised in respiration, water is produced, important for organisms like desert rats that do not drink water but survive on metabolic water from lipid intake
• Phospholipids


  • One of the fatty acids of a triglyceride is substituted by a phosphate group
  • The lipid part is non-polar and insoluble in water (hydrophobic)
  • The phosphate group is polar and dissolves in water (hydrophilic)
  • Important in cell membrane structure

  
• Proteins


  Polymers of amino acids - there are 20 different types of amino acids which differ by the R group

  
• Functions of proteins


  • Haemoglobin
  • Antibodies
  • Enzymes