Biological molecules

• Monomers


  Small units which are the components of larger molecules
• Polymers


  Molecules made from many monomers joined together
• Monomer joining


  1. Condensation reaction

  2. Water molecule eliminated
• Hydrolysis


  1. Opposite of condensation reaction

  2. Water added to break chemical bond
• Carbohydrates


  • Molecules consisting only of carbon, hydrogen and oxygen
  • Long chains of sugar units called saccharides
• Monosaccharide


  Single sugar unit
• Disaccharide


  Pair of monosaccharides
• Polysaccharide


  Many monosaccharides joined together
• Glycosidic bond


  Bond formed between monosaccharides in a condensation reaction
• Glucose


  • 6 carbon atoms per molecule
  • Main substrate for respiration
  • Has alpha and beta isomers
• Common monosaccharides


  • Glucose
  • Galactose
  • Fructose
• Disaccharide formation


  1. Condensation reaction of two monosaccharides

  2. Water molecule produced
• Polysaccharides


  Formed from many glucose units joined together
• Polysaccharides


  • Glycogen
  • Starch
  • Cellulose
• Glycogen


  • Main energy storage molecule in animals
  • Formed from alpha glucose
  • Has many side branches
  • Compact molecule to maximise energy storage
  • Insoluble to not affect water potential
• Starch


  • Energy storage in plants
  • Mixture of amylose and amylopectin
  • Amylose - unbranched, compact
  • Amylopectin - branched, can be broken down quickly
• Cellulose


  • Component of plant cell walls
  • Made of long, unbranched chains of beta glucose
  • Microfibrils form strong threads
  • Prevents cell wall bursting under osmotic pressure
• Benedict's test for reducing sugars


  1. Add 2cm3 of food sample

  2. Add 2cm3 of Benedict's reagent

  3. Heat mixture in water bath for 5 minutes

  4. Observe colour change to brick red (orange-brown)
• Benedict's reagent is an alkaline solution of Copper(II) Sulfate
• Reducing sugars can donate an electron to Benedict's reagent
• Benedict's test for non-reducing sugars requires hydrolysis with dilute HCl before testing with Benedict's reagent
• Iodine/potassium iodide test turns blue/black in the presence of starch
• Lipids


  Biological molecules made of carbon, hydrogen and oxygen which are only soluble in organic solvents
• Main lipid types


  • Triglycerides
  • Phospholipids
• Triglycerides


  • Made of one molecule of glycerol and three fatty acids joined by ester bonds
  • Fatty acids vary in chain length, presence and number of double bonds
• Saturated lipids


  Don't contain any carbon-carbon double bonds
• Unsaturated lipids


  Contain carbon-carbon double bonds, allowing them to bend and be liquid at room temperature
• Triglyceride structure


  • High ratio of energy storing carbon-hydrogen bonds to carbon atoms
  • Low mass to energy ratio
  • Insoluble in water
  • High ratio of hydrogen-oxygen atoms releases water when oxidised
• Phospholipids


  • One of the fatty acids of a triglyceride is substituted by a phosphate-containing group
  • Phosphate heads are hydrophilic, tails are hydrophobic, so they form micelles in water
• Margarine


  Butter
• Phospholipids


  • In an aqueous environment being polar means a bilayer can be formed
  • The hydrophilic heads of the phospholipids can be used to hold at the surface of the cell surface membrane
  • Their structure allows them to form glycolipids with carbohydrates which are important on the cell surface membrane for cell recognition
• Emulsion Test


  1. Take a completely grease free test tube and add 2cm3 of the sample to be tested and 5cm3 of ethanol

  2. Shake the test tube thoroughly to dissolve all the lipid in the solution

  3. Add 5cm3 of water and shake gently

  4. A cloudy-white colour indicates the presence of a lipid

  5. As a control repeat the experiment using water as the sample, the final solution should remain clear
• Phospholipids


  • In an aqueous environment being polar means a bilayer can be formed
  • The hydrophilic heads of the phospholipids can be used to hold at the surface of the cell surface membrane
  • Their structure allows them to form glycolipids with carbohydrates which are important on the cell surface membrane for cell recognition
• Emulsion Test


  1. Take a completely grease free test tube and add 2cm3 of the sample to be tested and 5cm3 of ethanol

  2. Shake the test tube thoroughly to dissolve all the lipid in the solution

  3. Add 5cm3 of water and shake gently

  4. A cloudy-white colour indicates the presence of a lipid

  5. As a control repeat the experiment using water as the sample, the final solution should remain clear
• Amino acids


  The monomers from which proteins are made
• Amino acids contain an amino group (NH2), carboxylic acid group (-COOH) and a variable R group which is a carbon-containing chain
• There are 20 different amino acids, each determined by their different R groups
• Amino acids are joined by peptide bonds formed in condensation reactions


  A molecule of water is formed
• Dipeptide


  Contains two amino acids
• Polypeptides


  Contain three or more amino acids