Cellular Energetics

• Enzymes


  Catalysts which speed up a biological reaction but are themselves unchanged by the reaction

  
• Without enzymes, reactions would occur very slowly
• Enzymes


  Globular proteins composed of one or more polypeptides, their 3D structure is affected by changes in temperature and pH
• Enzymes


  • Helicase
  • Amylase
• Enzymes as catalysts


  • They speed up reactions
  • They are unchanged by the reactions

  
• Metabolism


  The complex network of interdependent and interacting chemical reactions occurring in living organisms

  
• Role of enzymes in metabolism

  They carefully control the different metabolic reactions (anabolic and catabolic)
• Enzymes are specific to their substrate, so a large number of enzymes are required in organisms
• The use of enzymes in organisms makes biochemical reactions happen faster, making a lot of processes more efficient
• Anabolic reactions


  Building up complex molecules from simpler ones
• Catabolic reactions


  Breaking down complex molecules into simpler ones
• Catabolic reactions


  • Digestion of food
  • Cell respiration
  • Decomposition of complex carbon compounds

  
• Enzyme


  A globular protein which acts as a catalyst for biochemical reactions
• Active site


  A region on the surface of an enzyme to which substrates bind and which catalyzes the reaction

  
• The active site is composed of a few amino acids and binds to a specific substrate
• Enzyme-substrate specificity


  The 3D structure of the active site is specific to the substrate, and the chemical properties of substrate and enzyme attract through opposite charges

  
• Enzyme activity


  1. Substrate(s) bind to active site

  2. Bonds in substrate are stressed or weakened

  3. Products separate from active site

  
• Molecular motion


  The movement of enzymes and substrates which causes collisions between molecules
• All metabolic reactions occur in an aqueous solution, which enables dissolved molecules to have continual motion
• The speed of movement is affected by the molecule's size - substrates are usually smaller than enzymes, so their movement is faster
• The correct alignment and angle between substrate and enzyme affects the success of the collision
• Denaturation


  Changes in pH or temperature that alter the 3D structure of the enzyme, compromising enzyme-substrate specificity
• As temperature increases


  The rate of reaction increases as molecules have more kinetic energy, but above the optimum temperature enzymes denature
• As pH changes from the optimum


  The structure of the enzyme (including the active site) is altered, causing denaturation
• As substrate concentration increases

  The rate of reaction increases, but at the optimum concentration all active sites are full and working at maximum efficiency

  
• Activation energy


  The minimum amount of energy required for a chemical reaction to occur
• Enzymes lower the activation energy by weakening bonds already, so less energy is needed for an exothermic reaction to occur
• After the products have been formed, energy is released
• Uses of enzymes in industry


  • Detergents
  • Food industry
  • Brewing industry
  • Paper production
• Measuring enzyme-catalysed reactions


  1. Draw a tangent to the curve at a specified time to determine the rate

  2. The shape of the curve indicates the rate is fastest at the start and slows down as the reaction proceeds

  
• Intracellular and extracellular enzyme-catalysed reactions


  Enzyme catalysed reactions can take place inside or outside of cells
• Intracellular


  • Krebs cycle inside mitochondria

  
• Extracellular


  • Digestion of food in the small intestine

  
• Intracellular enzyme-catalysed reactions


  • Often inside organelles (e.g. mitochondria, nucleus) cytoplasm or bound to membranes where reactions are catalyzed by enzymes produced by free ribosomes in the cell
• Extracellular enzyme-catalysed reactions


  • Exoenzymes synthesized by the rER which are released from glands or specialized cells into the interior of an organ catalyzing the breakdown of larger macromolecules into monomers
• Metabolic reactions often result in the release of heat energy
• The additional energy is converted to heat
• Birds and mammals


  • Use the heat energy to maintain a body temperature greater than their environment
• Birds and mammals


  • Emperor penguins huddle together in groups to take advantage of the metabolic heat released by their neighbours
• Brown fat cells in adipose tissue


  • Contains more mitochondria than white fat cells or any other body tissue, allowing more energy to be generated through uncoupled respiration (without the production of ATP)