Topic 1

• 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

  
• Polymer breaking down


  1. Hydrolysis

  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


  Two monosaccharides joined together
• Polysaccharide


  Many monosaccharides joined together
• Glucose


  • Six carbon atoms in each molecule
  • Main substrate for respiration
  • Has alpha and beta isomers

  
• Common monosaccharides


  • Glucose
  • Galactose
  • Fructose

  
• Disaccharide formation


  1. Condensation reaction

  2. Water molecule produced

  3. 1,4 glycosidic bond between two alpha glucose molecules to form maltose

  
• Polysaccharides


  Formed from many glucose units joined together
• Polysaccharides


  • Glycogen
  • Starch
  • Cellulose
• Glycogen


  • Main energy storage molecule in animals
  • Formed from alpha glucose
  • Has 1,4 and 1,6 glycosidic bonds
  • Has many side branches
  • Compact molecule to maximise energy storage
  • Insoluble so doesn't affect water potential
• Starch


  • Energy storage in plants
  • Mixture of amylose (unbranched) and amylopectin (branched)
  • Amylose is coiled and compact
  • Amylopectin has 1,4 and 1,6 bonds allowing rapid breakdown
  • Insoluble so doesn't affect water potential
  • Compact so a lot of energy can be stored
• Cellulose


  • Component of plant cell walls
  • Made of long, unbranched chains of beta glucose
  • Microfibrils formed by parallel cellulose chains joined by hydrogen bonds
  • Provides structural support and prevents cell wall bursting
• Benedict's test for reducing sugars

  1. Add sample to Benedict's reagent

  2. Heat in water bath for 5 minutes

  3. Brick red precipitate indicates presence of reducing sugar

  
• Benedict's test for non-reducing sugars

  1. Add sample to Benedict's reagent, heat, no colour change

  2. Hydrolyse with dilute HCl to break down disaccharides/polysaccharides

  3. Neutralise with NaHCO3

  4. Retest with Benedict's reagent, colour change indicates non-reducing sugar

  
• Iodine test for starch

  Solution turns blue/black if starch is present
• Lipids


  Biological molecules made of carbon, hydrogen and oxygen, only soluble in organic solvents

  
• Triglycerides


  Lipids made of one glycerol and three fatty acids joined by ester bonds

  
• Saturated lipids


  • No carbon-carbon double bonds

  
• Unsaturated lipids


  • Contain carbon-carbon double bonds, can bend and are liquid at room temperature

  
• Triglyceride properties


  • High ratio of energy-storing C-H bonds
  • Low mass to energy ratio
  • Insoluble in water so don't affect water potential
  • Release water when oxidised
• Phospholipids


  One fatty acid substituted by a phosphate-containing group, form micelles in water

  
• Phospholipid properties


  • Polar structure allows bilayer formation
  • Hydrophilic heads can attach to cell surface membrane
  • Can form glycolipids for cell recognition

  
• Emulsion test for lipids

  Add sample to ethanol, shake, add water, cloudy-white colour indicates lipid presence
• Amino acids


  Monomers that proteins are made from, contain amino, carboxyl and R groups
• Peptide bond


  Bond formed between amino acids in a condensation reaction, releases water

  
• Dipeptide


  Two amino acids joined
• Polypeptide


  Three or more amino acids joined
• Protein structure


  • Primary - order and number of amino acids
  • Secondary - alpha helix or beta pleated sheet
  • Tertiary - 3D shape, maintained by disulfide bridges, ionic bonds, hydrogen bonds

  
• Primary structure of a protein

  The order and number of amino acids in a protein. This primary structure contains the initial sequence of amino acids and will therefore determine the proteins function in the end.
• Secondary structure of a protein

  The shape that the chain of amino acids makes – either alpha helix or beta pleated sheet. The hydrogen in the -NH has a slight positive charge whilst the oxygen in the -C=O has a slight negative charge. As a result weak hydrogen bonds can form leading to alpha helices or beta pleated sheets.

  
• Tertiary structure of proteins


  The 3D shape of the protein and is formed from further twisting and folding. A number of different bonds maintain the structure, these are: Disulfide bridges, Ionic bonds, Hydrogen bonds.
• Proteins


  • Can be globular or fibrous. Globular proteins such as enzymes are compact whereas fibrous proteins such as keratin are long and thus can be used to form fibres.
• Biuret Test


  1. Place the sample to be tested in a test tube and add an equal volume of sodium hydroxide at room temperature

  2. Add a few drops of very dilute (0.05%) copper (II) sulfate soliton and mix gently

  3. A purple colouration indicates the presence of a peptide bond and hence a protein. A negative result would mean the solution remains blue.
• Enzymes


  Increase rate of reaction by lowering the activation energy of the reaction they catalyse. They are 3D tertiary structured globular proteins whose shape is determined by the primary sequence of amino acids.
• Active site


  An area of the enzyme that is made up of only a few amino acids and forms a small depression in the overall enzyme. The molecule that the enzyme acts upon is called the substrate.
• Induced fit model


  When the enzyme and substrate bind they form an enzyme substrate complex, and the structure of the enzyme is altered so that the active site of the enzyme fits around the substrate.