BIOLOGICAL MOLECULES & ENZYMES

• Amino acids

  Small molecules from which proteins are assembled
• Enzymes

  Biological catalysts that increase the rate of metabolic reactions in living organisms
• Carbohydrates

  • Made of carbon, oxygen and hydrogen
  • Are polymers that break down into simple sugars
  • Molecules of repeating single sugars called saccharides (glucose)
• Proteins

  • Made of carbon, oxygen, hydrogen, sulfur, nitrogen and phosphorous
  • Are polymers (long chain molecules) that are broken down into its monomers (smaller basic units): amino acids
  • Large molecules made up of amino acids
• Lipids

  • Lipids (fats and oils) are made of carbon, oxygen and hydrogen
  • They are large polymers that are broken down into 3 fatty acids molecules and a glycerol molecule (smaller basic units)
• Glycogen

  A large carbohydrate made from many glucose molecules joined together. Serves as an energy store in animals
• Starch

  A large carbohydrate molecule made up of many glucose molecules. An energy storage molecule in plants
• Active site

  Part of the enzyme that is complementary to the shape of the substrate. The shape of the active site may change if the enzyme is exposed to high temperatures or extremes of pH
• Iodine test for starch:

  • Add orange-brown iodine solution to the food sample
  • If there is starch present the colour will change from orange-brown to blue-black
• Benedict's test for sugars:

  • Add blue Benedict's solution to the food sample
  • Heat the sample for 5 minutes at 70 degrees Celcius
  • If there is sugar present the colour will change from blue to green to yellow to red depending how much sugar there is in the sample (red would have the highest concentration)
• Sudan III test for lipids:

  • Add red Sudan III stain solution to the food sample
  • Shake the tube gently
  • If there are lipids present a bright red layer will form at the top of the liquid
• Biuret test for proteins:

  • Add blue Biuret solution to the food sample
  • Shake the tube
  • If there is protein present the colour will change from blue to purple
• Test for fats:

  • Add 2cm^3 of ethanol to the test solution
  • Add 2cm^3 of distilled water
  • If there is fat present the solution will go from colourless to forming a milky white emulsion
• Enzymes are biological catalysts, They are protein molecules and the shape of the enzyme is vital to its function. Each enzyme has its own uniquely shaped active site where the substrate binds

  Lock and key hypothesis:

  • The shape of the substrate is complementary to the shape of the active site so when they bind it forms an enzyme-substrate complex
  • Once bound (now enzyme-product complex), the reaction takes place and the products and enzyme are released from the surface of the active site
• Effect of temperature on enzyme function

  • The optimum temp is around 37 degrees Celcius (body temperature)
  • The rate of reaction increases with an increase in temperature up to this optimum, but above this temperature it rapidly decreases and eventually the reaction stops
  • When the temperature becomes too hot, the bonds in the structure will break
  • This changes the shape of the active site, so the substrate can no longer fit in
  • The enzyme is said to be denatured and can no longer work
• Practical: investigate how enzyme activity can be affected by changes in temperature

  1. Starch solution is heated to set a temperature
  2. Amylase is added
  3. Iodine is added after a minute
  4. Measure the time it takes until the iodine stops turning blue-black (this means that starch is not present as amylase has broken the starch down into glucose)
  5. Repeat the test with different temperatures
• Effect of pH on enzyme function

  • The optimum pH for most enzymes is 7, but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH
  • If the pH is too high or too low, the forces that hold the amino acid chains that make up the protein will be affected
  • This will change the shape of the active site, so the substrate can no longer fit in
  • The enzyme is said to be denatured and can no longer work
• Catalyst

  A substance which increases the speed of a reaction, without being changed or used up in the reaction