Enzymes

• An enzyme is a protein that increases the rate of reaction

  Enzymes are also known as biological catalysts
• The active site of an enzyme binds to the specific substrate
• Describe the lock and key mechanism of enzyme action

  The active site is like a lock and the substrate is like a key.

  In the same way, there is usually only one enzyme for every substrate (or one key for each lock).
• An enzyme is denatured if its structure is altered and it can no longer catalyse a reaction.
• Bile is an alkaline substance produced in the liver and stored in the gallbladder
• • Bile neutralises acid from the stomach to stop these enzymes from becoming denatured (lose their activity).
• What conditions do enzymes best operate in in the small intestine

  alkaline conditions
• Bile breaks up fats into tiny droplets through a process called emulsification.
• Bile breaks up fats (like oil) into tiny droplets, through a process called emulsification. The tiny droplets have a higher surface area than the original fat drop, which increases the rate of the reactions (catalysed by lipase) that break fats down.
• Amylase is a type of carbohydrase that can break down starch in our bodies
• The action sites of amylase are:

  • small intestine
  • mouth
• Amylase is produced in:

  • pancreas
  • salivary glands
• Amylase breaks down starch into its constituent simple sugars (predominantly maltose).
• Proteases are digestive enzymes that can break down proteins into amino acids.
• Protease is produced in:

  • pancreas
  • stomach
• action sites of protease are:

  • small intestine
  • stomach
• protease breaks down proteins into amino acids
• Lipase is a type of digestive enzyme that breaks down lipids into glycerol and fatty acids.
• Lipase is produced in:

  • small intestine
  • pancreas
• Test for starch

  Test:

  1. Put some of the food sample into a test tube.
  2. Add a few drops of iodine solution to the food sample using a pipette.
  3. If starch is present, the solution turns from brown to blue-black. Note any colour change in a table of results.
• Test for sugars

  Test:

  1. Add an equal volume or excess of Benedict’s solution to the food sample in a test tube.
  2. Place in a hot water bath for a few minutes.
  3. If sugar is present, a brick red precipitate is formed. If sugar is absent, the solution remains blue.
• Test for protein

  Test:

  1. Add a few drops of Biuret’s reagent (sodium hydroxide and copper (II) sulphate) to the food sample in a test tube.
  2. Shake the solution to mix and wait for a few minutes.
  3. If protein is present, the solution turns from blue to purple.
• Test for lipids

  Test:

  1. Add a few cm3 of ethanol to the food sample.
  2. Pour this mixture into a test tube of equal volumes of distilled water.
  3. If lipids are present, a white emulsion is formed on the surface of the mixture.
• Factors affecting rate of enzyme activity

  • pH
  • Temperature
  • Enzyme concentration
  • Substrate concentration
• Investigating the rate of enzyme activity

  1. Keep factors constant

  2. pH

  3. Temperature

  4. Enzyme concentration

  5. Substrate concentration
• effect of pHon enzyme activity

  Every enzyme has an optimum pH. Extremes of pH will cause the enzyme to denature. pH can be kept constant by using a buffer.
• Increasing temperatureeffect on enzyme activity

  Initially increases the rate of enzyme activity as the enzymes will have more kinetic energy
• Above a certain temperature

  Enzymes denature as the high temperature breaks the bonds holding together the enzyme
• Enzyme concentration

  Increasing the enzyme concentration increases the number of active sites available, which causes the rate of reaction to increase
• Substrate concentration

  Increasing the substrate concentration increases the rate of enzyme activity, as there are more substrate molecules to bind to the enzyme active site