enzymes

• the chemical reactions taking place

  in a cell are known as metabolic

  reactions. The sum of all the metabolic

  reactions is known as the metabolism

  of the cell. The function of enzymes is

  to catalyse metabolic reactions.
• Enzymes are biological catalysts. A catalyst is a

  chemical which speeds up a reaction without being used up itself. It takes

  part in the reaction, but afterwards is unchanged and free to catalyse more

  reactions
• Everything a cell does depends on which enzymes it can make, which in turn

  depends on which genes in its nucleus are working. They are

  necessary because the temperatures inside organisms are low (e.g. the human

  body temperature is about 37 °C) and without catalysts, most of the reactions

  that happen in cells would be far too slow to allow life to go on. The reactions

  can only take place quickly enough when enzymes are present to speed

  them up
• Substrate


  The molecule that an enzyme acts on
• Active site


  • A small area on the enzyme's surface where the substrate attaches
• Enzyme action


  1. Substrate attaches to active site

  2. Reaction takes place

  3. Products are formed

  4. Products leave active site
• Enzyme catalysis


  Lowers the energy needed for the reaction to start, allowing the products to be formed more easily
• Enzyme catalysis of large molecule formation


  1. Several substrate molecules attach to active site

  2. Reaction takes place

  3. Larger product molecule is formed

  4. Product leaves active site
• Lock and key model


  The substrate fits into the active site of the enzyme like a key fitting into a lock
• A substrate will only fit into the active site of a particular enzyme
• Enzymes are specific, i.e. an enzyme will only catalyse one reaction
• Biological


  Made in living cells
• Enzymes


  • Necessary to all living organisms
  • Maintain reaction speeds of all metabolic reactions at a rate that can sustain life
• Digestive enzymes


  • Without them, it would take 2-3 weeks to digest one meal
  • With enzymes, it takes around 4 hours
• The products of one reaction are often the reactants for another (and so on)
• Mechanism of enzyme action


  1. Enzymes are specific to one particular substrate(s)

  2. The active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate

  3. When the substrate moves into the enzyme's active site they become known as the enzyme-substrate complex
• Metabolic reactions

  The chemical reactions that take place in a cell; they are essential for the cell's survival and growth
• Metabolism

  The sum of all the metabolic reactions that occur in a cell; a measure of the cell's overall chemical activity and energy use
• Enzymes

  Proteins that catalyze metabolic reactions; they speed up the rate of these reactions and lower the amount of energy needed for them to occur