Enzymes

• Chemical reactions that take place in a cell are known as metabolic reactions.
• Metabolism is the sum of all the chemical reactions going on within the cell.
• Catabolic reactions: reactions in living organisms, which involve the breakdown of larger molecules and the release of energy.
• Anabolic reactions: a chemical reaction in living organisms, in which smaller molecules combine to form a larger one. Anabolic reactions require energy.
• Reactions are controlled by a group of proteins called enzymes.
• Enzymes are biological catalysts, meaning that they are made in living cells and speed up chemical reactions, while remaining unchanged at the end, so they are reused.
• Cells contain hundreds of different enzymes, each catalysing a different reaction.
• Enzymes are specific to the reaction they catalyse.
• What enzymes the cell can make is controlled by the nucleus, and in particular which genes are working.
• Why can we have thousands of different enzymes?

  Because there are many different genes coding for different enzymes and different combinations of amino acids can be joined together by peptide bonds to form different enzymes.
• Enzymes are made up of amino acids, joined together by peptide bonds and are folded into a 3D shape/structure.
• Enzymes are affected by temperature and pH.
• What is the active site?

  Small area on the surface of an enzyme where the specific substrate binds and products are formed.
• What is a substrate?

  Molecule upon which the enzyme acts, basically the reactant in an enzyme-catalysed chemical reaction.
• Lock and key model: Enzymes are specific to their substrate and have a complementary shape to the substrate
• When the substrate moves into the enzyme's active site, they are known as the ES complex or enzyme-substrate complex.
• After the reaction has occurred, the products leave the active site as they no longer fit it and the enzyme is free to take up another substrate.
• Extracellular enzymes-working outside the cell (e.g. digestive enzymes which are secreted by the intestine onto the food to break it down).
• Intracellular enzymes-working inside the cell (e.g. enzymes involved in the release of energy in the mitochondria).
• Why do we need enzymes?

  Many chemical reactions take place in the living organisms but they would occur too slowly at body temperature to keep organisms alive. Enzymes speed up these reactions.