1 - 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 whereby a water molecule is eliminated

  2. Hydrolysis is the opposite, water is added to break a chemical bond

  
• Carbohydrates

  Molecules which consist only of carbon, hydrogen and oxygen and they are long chains of sugar units called saccharides
• Monosaccharide

  A single sugar unit
• Disaccharide

  A pair of monosaccharides
• Polysaccharide

  Many monosaccharides joined together
• Glycosidic bond

  Bond formed between monosaccharides in a condensation reaction
• 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 between 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 so doesn't affect water potential
• Starch

  • Energy storage in plants
  • Mixture of amylose (unbranched) and amylopectin (branched)
  • Insoluble so doesn't affect water potential
  • Compact to store a lot of energy
  • Easily hydrolysed to release glucose
• Cellulose

  • Component of plant cell walls
  • Made of long, unbranched chains of beta glucose
  • Microfibrils form strong threads
  • Provides structural support and prevents cell bursting
• Benedict's test for reducing sugars

  1. Add sample to Benedict's reagent

  2. Heat in water bath

  3. Red precipitate indicates reducing sugar

  
• Benedict's test for non-reducing sugars

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

  2. Hydrolyse with HCl

  3. Neutralise with NaHCO3

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

  
• Iodine/potassium iodide test

  Blue/black colour indicates presence of starch
• 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 energy density
  • Low mass to energy ratio
  • Insoluble in water so don't affect water potential
  • Release water when oxidised
• Phospholipids

  One fatty acid replaced by a phosphate-containing group, forming a polar molecule
• Phospholipid properties

  • Form bilayers in aqueous environments
  • Hydrophilic heads can attach to cell surface membrane
  • Can form glycolipids for cell recognition

  
• Emulsion test for lipids

  1. Add sample to ethanol, then water

  2. Cloudy-white colour indicates presence of lipid

  
• 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, releasing 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.