enzymes

• what are enzymes Enzymes are biological catalysts

  Enzymes are globular proteins with complex and unique tertiary structures.

  They are known as biological catalysts because they increase the rate of a chemical reaction without being used up in the reaction itself. 
• Enzymes speed up reactions

  All chemical reactions require a certain amount of energy to get started. This is known as the activation energy, and is most often supplied in the form of heat. 

  Without sufficient activation energy, the reactant molecules will not have enough energy to break their bonds and form new ones to produce the desired products. Enzymes work by lowering the activation energy for a chemical reaction. This means that reactions are able to take place at a lower temperature (e.g. body temperature). 

  
• Intracellular enzymes and extracellular enzymes

  Enzymes can be grouped into two categories: intracellular enzymes and extracellular enzymes.

  Differences between intracellular enzymes and extracellular enzymes:

  • Intracellular enzymes - These act within the cells that produce them.
  • Extracellular enzymes - These act outside the cells that produce them, and are secreted
• Enzymes have unique tertiary structures which determine the shape of their active site.

  This shape is complementary to the substrate. 

  
• 2.the substrate binds to the active site to form an enzyme-substrate complex

  
• 3.temporary bonds form between the R groups within the active site and the substrate.

  These bonds lower the activation energy to help break down the substrate into products

  
• 4. the products are released from the active site, leaving the enzyme free to be used again.

  
• what are the 2 models of enzyme action

  In this model, the substrate fits perfectly into the enzyme's active site in the same way that a key fits into a lock.

  
• this model, the substrate does not fit perfectly into the enzyme's active site. As the substrate enters the enzyme, the active site changes shape slightly. This puts a strain on the substrate's bonds which lowers the activation energy.

  
• Enzyme denaturation

  Changes in temperature or pH can affect the rate of enzyme-catalysed reactions.Drastic temperature increases or changes to the pH causes bonds to break, changing the enzyme's tertiary structure.

  This causes the active site to change shape so that the substrate no longer fits. This means that enzymeDiagram showing enzyme denaturation where changes in temperature or pH cause the active site to change shape, preventing substrate binding.-substrate complexes cannot be formed and the enzyme is denatured. 

  
• Different factors affect the rate of enzyme-controlled reactions

  You need to be able to describe and explain how the four factors affect enzyme reactions.

  These factors are:

  1. Temperature 
  2. pH
  3. Substrate concentration 
  4. Enzyme concentration
• Temperature

  All enzymes have an optimum temperature, but these can vary. The graph below shows how temperature affects the rate of a specific enzyme-catalysed reaction.

  Explanation

  1. The molecules have more kinetic energy, causing more collisions and enzyme-substrate complexes.
  2. The optimum temperature is the temperature this enzyme works fastest at. 
  3. Too much kinetic energy causes the active site to change shape and the enzyme denatures.

  
• ph: all enzymes have an optimum pH, but these can vary. The graph below shows how pH affects the rate of a specific enzyme-catalysed n

  
• Description

  1. As the substrate concentration increases, the rate of reaction increases. 
  2. As the substrate concentration increases further, the rate of reaction plateaus (levels off).

  Explanation

  1. There are more substrate molecules to form more  enzyme-substrate complexes.
  2. This is the saturation point, which is when all active sites are occupied by a substrate and enzyme concentration becomes the limiting factor. 

  
• Description

  1. As the enzyme concentration increases, the rate of reaction increases. 
  2. As the enzyme concentration increases further, the rate of reaction plateaus (levels off).

  Explanation

  1. There are more enzyme molecules to form more enzyme-substrate complexes.
  2. All substrate molecules available are being acted upon and substrate concentration becomes the limiting factor.