Cell Metabolism

• Metabolism


  All the chemical reactions that occur within cells to keep us alive
• Catabolism


  Reactions in which larger molecules are broken down to form smaller molecules, releasing energy
• Anabolism


  Reactions in which smaller molecules are built up to form larger molecules, requiring energy
• Metabolism is concerned with maintaining balance between energy release and energy utilisation
• Enzymes

  Proteins that allow chemical reactions to take place at normal body temperature, acting as catalysts to speed up reactions without being consumed or permanently altered
• Activation energy


  The minimum energy required to initiate a chemical reaction between molecules
• Enzymes lower the amount of activation energy required for a reaction to begin
• How enzymes work


  1. Substrate binds to active site of enzyme to form enzyme-substrate complex

  2. Enzyme catalyses reaction

  3. Products are released
• Lock-and-key model


  The shape of the enzyme (key) is always complementary to the shape of the substrate (lock), fitting together exactly
• Induced-fit model


  When the enzyme and substrate join, they form weak bonds that cause the shape of the enzyme to change, forming complementary shapes
• Factors affecting enzyme activity

  • Concentration of enzyme
  • Concentration of substrate
  • Removal of products
  • Temperature
  • pH
  • Co-factors and co-enzymes
  • Enzyme inhibitors
• As temperature increases


  Enzyme activity increases
• Co-factors


  Inorganic molecules that make some enzymes active by changing the shape of the active site
• Co-enzymes


  Organic molecules that act as co-factors, changing the shape of the active site
• Enzyme inhibitors


  Substances that slow or stop enzyme activity, used by cells to control reactions
• Enzymes catalyze, or speed up, chemical reactions within the body that are required for life
• Cellular respiration is the process by which organic molecules, taken in as food, are broken down in the cells to release energy for cellular activity
• Glucose is the main food material utilised in cellular respiration
• Aerobic respiration


  1. Pyruvate converted to acetyl CoA

  2. Acetyl CoA enters citric acid cycle

  3. Electron transport system uses oxygen to convert glucose into carbon dioxide and water
• Anaerobic respiration


  Pyruvate from glycolysis is converted into lactic acid
• Anaerobic respiration only produces 2 ATP, while aerobic respiration can produce up to 38 ATP
• Only 40% of the energy from cellular respiration is incorporated into ATP, the remaining 60% is lost as heat
• Energy must continually be consumed as food to replace what is lost as heat
• Metabolism


  The chemical processes that occur within a living organism in order to maintain life
• Anabolism


  1. The building of large new molecules of many smaller ones

  2. e.g. protein synthesis
• Amino acids


  Smaller units that make up polypeptides
• Polypeptides


  Larger molecules made up of amino acids
• Anabolic reactions usually require energy
• Catabolism


  1. The breaking down of larger molecules into many smaller ones

  2. e.g. cellular respiration
• Catabolic reactions generally release energy
• Activation Energy


  The energy needed to get chemical reactions started, even those which will result in the release of energy
• Burning (combustion)


  • An example of an energy-releasing catabolic reaction
• Cell respiration is very similar to burning
• Cellular respiration


  1. glucose + oxygen —> water + carbon dioxide

  2. A complex process involving over 20 steps
• Enzymes


  • Special protein molecules which make metabolic reactions happen much faster than they otherwise would at body temperature
  • They do this by lowering the activation energy needed to begin a reaction
• Every single metabolic reaction in your body requires an Enzyme to make it happen
• Enzymes catalyse reactions, speeding up cell reactions without getting used up in the chemical reaction
• Lock and Key model


  The enzyme (key) is shaped to fit the substrate (lock)
• Substrate


  The molecule the enzyme acts upon
• Enzymes are specific and will combine with one particular substrate and therefore are only involved with one reaction