3.1.4.2 Many proteins are enzymes

• Enzymes- speeds up chemical reactions by lowering the activation energy, so less energy is required for bonds to be broken or formed
• Activation energy- minimum amount of energy required for a reaction to take place

  A) no

  B) with

  C) substrate

  D) products

  
• Active site- specific shape, determined by the tertiary structure of the enzyme, specific to substrate
• If the tertiary structure of an enzyme changes, the active site also changes. This causes the enzyme to denature, and the enzyme no longer works since the enzyme is no longer complementary to the substrate as it's shape is different, so enzyme-substrate complexes can't be formed and the reaction is not catalysed.
• An enzyme's active site is complementary to it's specific substrate. When an enzyme binds to a substrate, an enzyme-substrate complex is formed, and the substrate is able to be changed into a product, due to the stress being put onto the bonds in the substrate and breaking them.
• Induced-fit model- the model where the active site changes shape slightly to fit the similar substrate. When bound, an enzyme-substrate complex forms, resulting in the pressure (from the active site changing) breaking the bonds in the substrate, forming products.
• Factors that affect enzyme activity:

  • Temperature
  • pH
  • Substrate concentration
  • Enzyme concentration
  • Enzyme inhibitors
• Temperature:

  If the temperature is too low, there will be less kinetic energy in the particles, so they cannot successfully collide to reach activation energy and there will be a lower rate.

  At optimum temperature, there are enough successful collisions to reach the lowered activation energy, and enzymes remain active, so the maximum number of enzyme-substrate complexes are formed.

  If the temperature is too high, the high energy will break the bonds within the enzymes tertiary structure, changing the active site, so enzyme-substrate complexes form less and the rate of reaction decreases.
• pH:

  pH's which aren't optimum pH can break hydrogen and ionic bonds, which changes the tertiary structure. This means the active site is changed so the substrate won't bind as much to the active site, less enzyme-substrate complexes are formed and the rate decreases.
• Enzyme concentration:

  The concentration of enzyme in a solution is directly proportional to the rate of reaction, as long as the substrate is also the same concentration so enzyme-substrate complexes can be formed
• Substrate concentration:

  The concentration of substrate in a solution is directly proportional to the rate of reaction up to a point, until each enzyme is taken up by a substrate, and therefore becoming the limiting factor, keeping the rate at the same level
• Competitive inhibitor- similar shape to the substrate, so it is almost complementary to the active site, binds to active site to block enzyme-substrate complexes from forming
• What type of inhibitor is this?

  A) active

  B) substrate

  C) enzyme

  D) competitive

  
• Non-competitive inhibitors- binds to the enzymes structure, away from the active site, which changes the tertiary structure and the active site, so enzyme-substrate complexes can't be formed
• What type of inhibitor is this?

  A) non-competitive

  B) enzyme

  C) active

  D) substrate

  
• Inhibitors:

  A) without

  B) inhibitor

  C) competitive

  D) non-competitive

  
• Intracellular enzyme- produced in certain cells and remain there to be used in that cell
• Extracellular enzyme- produced in a cell, but then transported outside the cell to be used there