1. Biological Molecules

• The biochemical basis of life is similar for all living things
• Monomers


  Smaller units from which larger molecules are made
• Polymers


  Molecules made from a large number of monomers joined together
• Monomers


  • Monosaccharides
  • Amino acids
  • Nucleotides
• Condensation reaction


  Joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water
• Hydrolysis reaction


  Breaks a chemical bond between two molecules and involves the use of a water molecule
• Monosaccharides


  The monomers from which larger carbohydrates are made
• Common monosaccharides


  • Glucose
  • Galactose
  • Fructose

  
• Condensation reaction between two monosaccharides


  Forms a glycosidic bond
• α-glucose and β-glucose


  Isomers of glucose with different structures

  
• Polysaccharides


  • Glycogen (α-glucose)
  • Starch (α-glucose)
  • Cellulose (β-glucose)

  
• Glycogen


  • Made up of α-glucose monomers
  • Branched so more ends for enzyme action
  • Coiled, so makes molecule compact
  • Has 1,4- and 1,6-glycosidic bonds
  • Insoluble in water, so doesn't affect water potential
  • Polymer of (α-) glucose so provides glucose for respiration
  • Large molecule, so can't cross the cell membrane

  
• Starch


  • Formed from α-glucose
  • Position of hydrogen and hydroxyl groups on carbon atom 1 inverted
  • Insoluble in water, so doesn't affect water potential
  • Branched/coiled/(α-)helix, so makes molecule compact
  • Polymer of (α-)glucose so provides glucose for respiration
  • Branched/more ends for fast breakdown/enzyme action
  • Large molecule, so can't cross the cell membrane

  
• Cellulose


  • Made up of β-glucose monomers
  • Has straight chain
  • Has only 1,4-glycosidic bonds
  • Long and straight chains
  • Become linked together by many hydrogen bonds to form fibrils
  • Provide strength to the cell wall

  
• Biochemical test for starch


  Add iodine in potassium iodide solution, colour changes from yellow to blue-black
• Biochemical test for reducing sugars


  Heat in Benedict's solution, red/green/orange precipitate/colour
• Biochemical test for non-reducing sugars


  Heat with acid and neutralise, then heat with Benedict's solution, red precipitate/colour
• Groups of lipids


  • Triglycerides
  • Phospholipids
• Condensation reaction between glycerol and a fatty acid


  Forms an ester bond
• Saturated fatty acid


  No double bonds between carbons
• Unsaturated fatty acid


  At least one double bond between carbons
• Triglycerides


  • Easily hydrolysed to fatty acids and glycerol, then respired to make ATP
  • A high number of energy-storing carbon-hydrogen bonds
  • Non-polar, therefore insoluble, so they don't affect water potential
  • Low mass to energy ratio, so they can be stored in a small volume
• Phospholipids


  • Hydrophilic head groups are attracted to water in aqueous environment
  • Hydrophobic tail groups are oriented away from water
  • Polar nature means they form phospholipid bilayers
  • Easily combine with carbohydrates, forming glycolipids
• Emulsion test for lipids


  Mix/shake the sample with ethanol, then add water, white/milky emulsion
• Amino acid


  The monomers from which proteins are made, with a general structure of NH2, COOH, and R (side chain)

  
• Condensation reaction between two amino acids

  Forms a peptide bond
• Dipeptide


  Formed by the condensation of two amino acids
• Polypeptide


  Formed by the condensation of many amino acids
• Functional protein


  May contain one or more polypeptides
• Protein structure


  • Hydrogen bonds, ionic bonds and disulfide bridges form the overall 3D shape (tertiary structure)

  
• Levels of protein structure

  • Primary: order of amino acids
  • Secondary: alpha helices or beta pleated sheets
  • Tertiary: overall 3D shape
  • Quaternary: multiple polypeptides join together

  
• Biuret test for proteins

  Add biuret reagent, colour changes from blue to purple
• Enzyme


  Lowers the activation energy of the reaction it catalyses
• Induced-fit model of enzyme action

  1. Substrate binds to active site forming enzyme-substrate complex

  2. Active site changes shape slightly to be complementary to substrate

  3. Reduces activation energy
• Enzyme properties


  • Specificity - active site has a specific shape complementary to its substrate
  • Effects of enzyme concentration, substrate concentration, competitive/non-competitive inhibitors, pH, and temperature
• Enzyme concentration increases


  Successful collisions increase until there is too little substrate to fill the active sites and the rate plateaus
• Substrate concentration increases


  Successful collisions increase until every active site is saturated with substrate and the rate plateaus
• Competitive inhibitors


  Reversibly bind the active site, reducing the rate of reaction by inhibiting formation of E-S complexes
• Non-competitive inhibitors


  Bind away from the active site, disrupting the tertiary structure of the active site, preventing E-S complexes from forming
• Change in pH away from optimum


  Alters the charges of amino acids, the further from optimum the more it denatures the enzyme