TOPIC 1 BIOLOGY

• Disaccharides

  • Maltose
  • Sucrose
  • Lactose
• Maltose

  Disaccharide formed by condensation of two glucose molecules
• Sucrose

  Disaccharide formed by condensation of glucose & fructose
• Lactose

  Disaccharide formed by condensation of glucose & galactose
• Polysaccharides

  • Glycogen
  • Starch
  • Cellulose
• Glycogen

  Main energy storage molecule in animals, formed from many molecules of alpha glucose joined by 1,4 and 1,6 glycosidic bonds, has many side branches
• Starch

  Energy storage molecule in plants, mixture of amylose (unbranched chain of glucose) and amylopectin (branched chain of glucose)
• Cellulose

  Component of plant cell walls, composed of long, unbranched chains of beta glucose joined by glycosidic bonds, forms strong microfibrils
• Benedict's test for reducing sugars

  1. Add sample to Benedict's reagent, heat, observe colour change to brick red

  2. If no colour change, hydrolyse sample with HCl, neutralise, then retest
• Benedict's reagent

  Alkaline solution of Copper(II) Sulfate, forms insoluble red precipitate (copper(I) oxide) with reducing sugars
• Iodine/potassium iodide test for starch


  Add iodine/potassium iodide solution, observe colour change to blue/black
• Lipids

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

  • Triglycerides
  • Phospholipids
• Triglycerides

  Lipids made of one glycerol molecule and three fatty acids joined by ester bonds
• Saturated lipids

  Lipids without carbon-carbon double bonds
• Unsaturated lipids

  Lipids with carbon-carbon double bonds, can bend and are liquid at room temperature
• Triglycerides

  • High ratio of energy-storing C-H bonds, low mass to energy ratio, insoluble in water, release water when oxidised
• Phospholipids

  One fatty acid in triglyceride replaced by phosphate-containing group, form bilayers in aqueous environments
• Emulsion test for lipids

  Add sample to ethanol, add water, observe cloudy-white colour
• Amino acids

  Monomers that make up proteins, contain amino, carboxyl and variable R groups
• Formation of peptide bonds

  Amino acids joined by condensation, releasing water
• Protein structure

  Primary (sequence of amino acids), secondary (alpha helix, beta sheet), tertiary (folding stabilised by bonds), quaternary (multiple polypeptide chains)
• Biuret test for proteins

  Add sample to NaOH, add CuSO4, observe purple colour
• Enzymes increase the rate of chemical reactions
• Cysteine

  Strong and not easily broken
• Ionic bonds

  • Form between the carboxyl and amino groups that are not involved in the peptide bond
  • Easily broken by pH
  • Weaker than disulfide bridges
• Hydrogen bonds

  • Numerous and easily broken
• Globular proteins

  Compact, such as enzymes
• Fibrous proteins

  Long and can be used to form fibres, such as keratin
• Biuret Test

  1. Place sample in test tube

  2. Add sodium hydroxide

  3. Add copper (II) sulfate

  4. Purple colouration indicates presence of peptide bond and protein
• Enzymes

  • Increase rate of reaction by lowering the activation energy
  • 3D tertiary structured globular proteins
  • Active site is an area made up of a few amino acids
• Substrate

  The molecule that the enzyme acts upon
• Induced fit model

  When the enzyme and substrate bind, the structure of the enzyme is altered so that the active site fits around the substrate
• As temperature increases

  • Rate of reaction increases up to the optimum temperature
  • Rate of reaction decreases beyond the optimum temperature as the enzyme becomes denatured
• pH

  • Measure of hydrogen ion concentration
  • Affects the enzyme's shape by disrupting bonds in the tertiary structure
• As enzyme concentration increases

  Rate of reaction increases as there are more active sites for substrates to bind to
• As substrate concentration increases

  Rate of reaction increases as more enzyme-substrate complexes are formed
• As concentration of competitive reversible inhibitors increases

  Rate of reaction decreases as the active sites are temporarily blocked
• As concentration of non-competitive reversible inhibitors increases

  Rate of reaction decreases as the shape of the enzyme (not the active site) is altered
• DNA

  Carries genetic information