Biological Molecules

• Condensation reaction


  When two monosaccharides react to form a disaccharide, a molecule of water is removed (from a hydroxyl group on one sugar and a hydrogen on another) and a glycosidic bond forms
• Monosaccharides


  Consist of a ring structure with the general formula CH2O. Glucose is a hexose sugar with six carbon atoms, and can exist as alpha or beta forms
• Ribose


  A pentose monosaccharide with five carbon atoms, a component of RNA molecules
• Glycogen


  Branched chains of alpha glucose, similar to amylopectin but with more side-branches, giving a large surface area for enzyme action
• Lipids


  Triglycerides, phospholipids and cholesterol
• Triglycerides


  Made up of glycerol connected to three fatty acid 'tails' through ester bonds, used as an energy store
• Phospholipids


  Made up of glycerol connected to two fatty acid 'tails' and a phosphate group through ester bonds, the main component of cell membranes
• Cholesterol


  Found in cell membranes, helps to strengthen the membrane by pushing the hydrophobic tails of phospholipids closer together
• Reducing sugar


  Any sugar that can act as a reducing agent because of its aldehyde or ketone group, including all monosaccharides and some disaccharides
• Testing reducing sugars using Benedict's solution


  Reducing sugars will change the solution colour from blue to green/yellow/orange/brick red, depending on the concentration
• Testing for non-reducing sugars like sucrose

  Break down the sample into monosaccharides using hydrochloric acid, neutralise, then perform the Benedict's test
• Testing for starch using iodine


  Starch will turn the solution from orange/brown to blue/black
• Biuret test


  1. Adding sodium hydroxide to a sample followed by copper sulfate solution

  2. A colour change from blue to purple indicates a positive result
• Enzyme active site


  Region of the enzyme that has a specific shape and allows the substrate to bind
• Induced fit model


  The shapes of the enzyme's active site and its substrate are not exactly complementary, but when the substrate enters the active site, a conformational change (change of shape) occurs which induces catalysis
• As enzyme concentration increases

  The rate of reaction increases
• As substrate concentration increases

  The rate of reaction increases
• As temperature increases


  The rate of reaction increases
• Competitive inhibitors


  Bind to the active site of the enzyme, blocking the substrate from binding
• Measuring product formation using catalase

  1. Add hydrogen peroxide, buffer solution and catalase

  2. Measure the volume of oxygen produced over time

  3. Calculate the initial reaction rate from the graph
• Measuring reactant removal using amylase

  1. Add starch solution and iodine solution

  2. Add amylase and measure the absorbance over time

  3. Calculate the initial reaction rate from the graph