Introduction to enzymes

• what is the structure of a globular protein?

  • hydrophobic amino-acids R groups in the centre
  • hydrophilic amino-acid R groups on the outside
  • specific tertiary structure and soluble in water
• what is a catalyst?

  a substance that increases the rate of chemical reactions without being used up
• what does the specific feature of an enzyme mean?

  catalyse reactions involving one or only a few types of substrate
• what is the active site?

  • a pocket or cleft where the substrate binds
  • area of the enzyme where the catalytic activity occurs
• how are enzymes affected by temperature and pH?

  they are denatured by high temperature or extremes of pH
• what is the size of an enzyme?

  relatively larger, consisting of several hundred amino acids
• what is the function of most amino acids?

  maintaining the specific tertiary structure of the enzyme
• how many amino acids are in the active site?

  very few, often fewer than 10
• what is the shape of the active site?

  the complementary shape to the specific substrate, depends on the sequence of amino acids in primary structure
• what is a limit to reaction rate?

  • activation energy
  • how fast the substrate collides with the active site
• what are the commercial applications of enzymes in biological washing powders and detergents?

  • lipases break down fats and oils, while protease work to break down protein chains
  • food stains are insoluble molecules so enzymes are needed to covert stain molecules into soluble molecules
• what are the commercial applications of enzymes in food processing?

  • break down complex molecules making them more accessible for babies (protease)
  • easier to absorb amino acids
  • creates smoother baby food easier to swallow
• what are the commercial applications of enzymes in beverages?

  • breaks down pectin, leading to higher yield of juice and prevents cloudiness (hydrolysis)
  • reduces need for harsh chemicals - easier to extract juice from cytoplasm
• what are the commercial applications of enzymes in production of bioethanol?

  • used to convert starches (amylase/glucoamylase) into ethanol
  • more eco friendly
  • higher yield and efficiency
  • renewable
• what are the advantages of using enzymes over inorganic catalysts like metals?

  • unlike using inorganic catalysts like metals, enzymes are more specific and do not produce a range of unwanted by-products
• what is the generic equation for enzyme-controlled reactions?

  enzyme + substrate -> enzyme + product
• why are enzymes important in biology?

  they catalyse nearly all reactions occurring within cells and many outside of cells, they drive metabolism, these reactions would require high temperatures and pressures without enzymes
• how do you work out the name of an enzyme?

  the name is usually derived from the substrate of the reaction that is catalysed, with the suffix 'ase'
• what are some examples of enzymes and the reaction they catalyse?

  • Lactase - lactose -> glucose + galactose
  • Catalase - hydrogen peroxide -> water + oxygen (is toxic and needs to be broken down)
  • ATP-ase - ATP -> ADP + phosphate (releases energy for processes like active transport)
• what are anabolic reactions?

  • building of smaller molecules into larger molecules
  • the forming of bonds
  • requires energy
• what is a catabolic reaction?

  • the breaking up of a larger molecule into a smaller molecule
  • releases energy
  • breaking bonds
• why do enzymes rarely work in isolation?

  they work as a part of multi-step pathways (cascades) in order to control the chemical reaction in our body (metabolism)
• what is metabolism?

  the sum of all reactions and reaction pathways happening in a cell or organism
• why are enzymes specific in the reactions they catalyse?

  • enzymes have a shape (active site) which is specific for a specific substrate shape, if they weren't specific then enzymes may begin to catalyse the wrong reaction
  • substrate has as specific 3-D shape which is complementary to enzyme active site
  • each enzyme has a specific primary structure, which will affect the overall 3-D shape (tertiary structure) and therefore the shape of the active site
• what enzyme breaks glyosidic bonds?

  amylase - hydrolysis of the alpha-1, 4-glycosidic bonds found in amylose
• what enzyme breaks up ester bonds?

  lipase - hydrolyses the ester bonds found in triglycerides
• what is an intracellular enzyme?

  enzymes which catalyse reactions inside cells, either attached to cell membranes or free in cytoplasm
• what is an extracellular enzyme?

  enzymes which are released from cells and catalyse reactions outside the cell
• what is a heterotroph?

  organisms that obtain their nutrients by consuming other organisms, they need to use enzymes to digest their food
• what are some intracellular enzymes?

  • DNA helicase
  • catalase
  • rubisco
  • ATPase
  • DNA polymerase
  • RNA polymerase
• what is the brief process of phagocytosis?

  • some phagocytes engulf invading microbes like bacteria
  • the endocytosed vesicles (containing hydrolytic enzymes) is fused with one of many lysosomes present and lysomal enzymes digest bacterium (forming a phagolysosome)
• what are some extracellular enzymes?

  • amylase
  • protease
  • lipase
  • lactase
• why does mould need to secrete enzymes in order to receive a supply of nutrients?

  • molecules are too big (starch) so needs to be broken down into glucose to be absorbed
  • too large to cross membrane and are insoluble so need to be hydrolysed into smaller soluble molecules which can then enter the cell
• what are the advantages of having an internal digestive system over a moulds external digestive system?

  • don’t need to use energy to get food back in (through active transport)
  • enzymes won’t return to mould so will need to use more energy to make new enzymes
  • makes mould more tired/fatigue
  • will get all the food/nutrients broken down in digestion (mould wont as it’s extracellular and is available to other organisms)