Biological molecules

• Monosaccharides


  Single monomer
• Properties of Monosaccharides

  • Sweet-tasting
  • Soluble substances
  • General formula (CH2O)n
• Examples of Monosaccharides

  • Glucose
  • Galactose
  • Fructose
• Glucose


  • Hexose (6-carbon) sugar
  • Formula C6H12O6
  • Has two isomers
• Disaccharides are formed by condensation reactions between two monosaccharide units with the elimination of water.
• Monosaccharides have the general formula Cn(H2O)n
• The three types of carbohydrates are monosaccharides, disaccharides, and polysaccharides.
• The most common disaccharides include sucrose, lactose, and maltose.
• Polysaccharides consist of many monosaccharide units joined together through glycosidic bonds.
• Activation energy


  The minimum amount of energy needed to activate the reaction
• Enzyme action


  1. Enzymes work as catalysts by lowering the activation energy

  2. Enzyme structure: Enzymes have a specific 3-D shape that is the result of their sequence of amino acids

  3. Active site: A specific region of the enzyme made up of a small number of amino acids

  4. Enzyme-substrate complex: The molecule on which the enzyme acts is called the substrate
• Enzymes


  • Enzymes have a specific 3-D shape
  • Enzymes have an active site made up of a small number of amino acids
• Rise in temperature


  Increases the kinetic energy of molecules
• Increased kinetic energy of molecules


  Molecules move around more rapidly and collide with each other more often
• More successful collisions between enzyme active site and substrate

  Rate of reaction increases
• Continued temperature rise


  Breaks hydrogen and other bonds in the enzyme molecule
• Breaking of bonds in enzyme molecule

  Changes the shape of the enzyme, including the active site
• Changed active site shape


  Slows the rate of reaction
• Further temperature rise


  Enzyme becomes denatured and stops working
• Triglycerides


  Molecules with three fatty acids combined with glycerol
• Formation of triglycerides


  1. Each fatty acid forms an ester bond with glycerol in a condensation reaction

  2. Hydrolysis produces glycerol and 3 fatty acids
• Fatty acids in triglycerides

  • If no carbon-carbon double bonds, the fatty acid is saturated
  • If one double bond, the fatty acid is monounsaturated
  • If more than one double bond, the fatty acid is polyunsaturated
• Properties of triglycerides


  • High ratio of energy-storing carbon-hydrogen bonds to carbon atoms, making them an excellent source of energy
  • Low mass to energy ratio, making them good storage molecules
  • Large, non-polar molecules, so insoluble in water and do not affect osmosis
  • High ratio of hydrogen to oxygen atoms, so release water when oxidised, providing an important water source
• Disaccharides


  Molecules formed when two monosaccharides are combined
• Formation of disaccharides


  1. A molecule of water is removed, and the reaction is a condensation reaction

  2. The bond formed is called a glycosidic bond
• Breaking down disaccharides


  Addition of water, a reversible reaction
• Induced fit model


  The active site forms as the enzyme and substrate interact, with the enzyme changing shape to fit the substrate
• Enzyme-substrate complex


  Puts a strain on the substrate molecule, lowering the activation energy needed to break bonds
• Competitive inhibitors


  Have a molecular shape similar to the substrate, allowing them to occupy the active site and compete with the substrate
• Increased substrate concentration


  Reduces the effect of the competitive inhibitor
• Non-competitive inhibitors


  Attach to the enzyme at a site other than the active site, altering the shape of the enzyme and preventing substrate binding
• Increased substrate concentration


  Does not decrease the effect of the non-competitive inhibitor
• Emulsion test for lipids

  1. Add sample to ethanol, then water

  2. A cloudy white colour indicates the presence of lipids
• The cloudy colour is due to lipids being finely dispersed in the water to form an emulsion
• Test for non-reducing sugars

  1. Hydrolyse the sample in dilute hydrochloric acid

  2. Neutralise with sodium hydrogen carbonate

  3. Test the resulting solution with Benedict's reagent
• If a non-reducing sugar was present

  Benedict's reagent will turn orange-brown
• Test for starch


  1. Add iodine solution to the sample

  2. A blue-black colour indicates the presence of starch
• Test for reducing sugars

  1. Add sample to Benedict's reagent and heat

  2. An orange-brown precipitate indicates the presence of reducing sugars
• Biuret test for proteins

  • Add sodium hydroxide and copper(II) sulfate to the sample
  • A purple colour indicates the presence of peptide bonds and hence proteins
• All monosaccharides and some disaccharides are reducing sugars