Enzymes glossary

Enzymes glossary

1. Enzymes

   • Enzymes are globular proteins that are catalysts. The are called biological catalysts as they are made by living cells.
     • Enzymes and chemical catalysts share properties in the reaction they catalysts:
       • E.g
         • They speed up reactions
           • They are not used up
             • They are not changed
               • They have a high turn over-over unit which means that they catalyse many reactions per second
     • Enzymes only catalyse reactions that are energetically favourable and would happen anyway
       • But without enzymes, reaction in cells would be too slow to be compatible with life
   • Enzymes are proteins with tertiary structure and the protein chain folds into a spherical globular shape with the R groups on the outside of the molecule, thus making enzymes soluble.
     • Each enzyme has a particular sequence of amino acids, and the other elements in the R groups determine the bonds the amino acids the make with each other.
       • These are hydrogen bonds, disulphide bridges and ionic bonds and they hold the enzyme molecule in its tertiary form.
         • A small area with a specific 3D shape is the active sited it gives the enzyme many of its properties

2. Metabolism

   • The term 'metabolism' refers to all the reactions of the body. Reactions occur in sequences called "Metabolic pathways"
     • These include:
       • Anabolic reactions, building up molecules (e.g protein synthesis)
         • Catabolic reactions, breaking molecules (e.g digestion). Metabolic pathways are controlled by enzymes. The products of one enzyme controlled reaction become the reactants in the next

3. Sites of enzyme action:

   • Extracellular
     • Intracellular, in solution
       • Intracellular, membrane-bound
         • Intracellular enzymes may be attached to membranes, for example, on the cristal of mitochondria and they transfer electrons and hydrogen ions in ATP formation.
       • Intracellular enzymes act in solution inside cells (E.g enzymes that catalyse glucose breakdown in glycolysis, a stage of respiration in solution in the cytoplasm; enzymes in solution in the storm of the chloroplasts catalyse the synthesis of glucose
     • Some enzymes are secreted from cells by exocytosis and catalyse extracellular reactions.
       • Amylase, made in the salivary glands, moves down the salivary ducts to the mouth. Saprotrophic fungi and bacteria secrete amylases, lipase sand protease son to their food, which digest it and they absorb the products of digestion

4. Active site

   • An enzyme acts on its substrate, with which it makes temporary bonds at the active site, forming an enzyme-substrate complex. When the reaction is complete, products are released, thus leaving the enzyme unchanged and leaves the active site ready to reciceve another substrate molecule
     • Active site: The specific 3D site on an enzyme molecule to which the substrate binds by weak chemical bonds
     • Enzyme-substrate complex:intermediate structure formed during an enzyme-catalysed reaction in which the substrate and enzyme bind temporarily, such that the substrates are close enough to react