Enzymes (2.5-2.6)

  • Anabolic: Reactions that @@build@@ large molecules from smaller ones
    • Require an input of energy
  • Catabolic: Reactions that @@break down@@ large molecules into smaller ones
    • Release energy

Enzymes

  • Enzymes: Biological catalysts made up of proteins that speed up the rate of chemical reactions and remain unchanged

  ### Feautures of Enzymes

  • Enzymes are biological catalysts made of proteins
  • Needed in small amounts to catalyse large molecules
  • Name after the suffix ‘-ase’
  • Specific in action. Each enzyme can act on a specific substrate because of the enzyme-substrate complex; have active sites where substrates can fit
  • Convert substrates into products
    • Enzymes are necessary to all living organisms as they maintain reaction speeds of all metabolic reactions at a rate that can sustain life
    • Substrate: The substance on which an enzyme acts on

 

Types of enzymes
  1. Intra-cellular enzymes: Are formed inside the cell and working inside eg. Catalase
  2. Extra-cellular: Are formed inside the cell but work outside eg. Lipase, amylase

Enzyme Activity

  • An enzyme is a protein folded into a complex 3D shape
  • The Active site is the part of the enzyme that allows it to act as a catalyst
  • Lock and key hypothesis- When the substrate moves into the enzyme’s active site they become known as the enzyme-substrate complex
  1. Substrate molecules fit exactly into the active site of the enzyme to form an enzyme substrate complex
    • The active site brings the molecules closer to allow them to react
  2. The substrate reacts to form a product which leaves the active site
  3. The enzyme is now free to bind with more molecules

 

  • Enzymes lower the energy needed for the reaction to take place

 

Factors affecting enzyme activity

  1. Temperature
  • Enzyme activity increases with a rise in temperature up to a certain point
  • Higher temperatures speed up the movement of substrate molecules
  • They will collide more often and with more energy and are more likely to bond to the active site
  • Eventually the enzyme molecules vibrate so much that they become denatured (lose their shape)

 

  • Each enzyme has an optimum temperature
    • Temperature at which enzyme activity is highest
    • Human enzymes - 37C
    • Plant Enzymes- 25C

 

  1. pH
  • Each enzyme has its own optimum pH
    • pepsin - pH 2.0 (acidic)
    • Amylase - pH 7.5 (slightly basic)
  • Activators: make binding more likely. eg. chloride ions are essential for the activity of amylase
  • Inhibitors: Make bindidng more difficult by covering the active site of the enzyme. eg. Cyadine ions, block respiratory enzymes

 

Uses of enzymes

  • Snake venom can break down blood clots
  • Lactase can break down lactose to make lactose free milk

Experiment

  • Catalase catalyses the breakdown of hydrogen peroxide
    • Hydrogen peroxide→ Oxygen + Water
  1. Discs of potato are put into a solution of hydrogen peroxide
  2. The catalase in the potatoes breaks down the hydrogen peroxide into oxygen and water
  3. The oxygen passes into the manometer which shows how much oxygen is being produced
  4. This gives a measure of enzyme activity