Unit 3 Cellular Energetics

• Enzymes


  Proteins that act as biological catalysts
• Enzymes


  • Catalyze (speed up) most chemical reactions that occur within a cell
  • Help reduce the activation energy
  • Typically, reactions resulting in a net release of energy require less activation energy compared to reactions resulting in net absorption of energy
  • They are reusable and not chemically changed by the reactions

  
• Enzyme names


  Often indicate the substrate or chemical reactions involved (e.g. sucrase digests sucrose)

  
• Enzyme catalysis


  1. Substrate binds onto the active site

  2. Reaction occurs and substrate transforms into products

  3. Products are released from the active site

  
• Enzyme structure


  • Typically has one active site, usually a pocket or crevice formed by the folding of a protein
  • Each enzyme can only catalyze one chemical reaction with only one substrate
• Inhibitors


  Molecules that interfere with the functioning of an enzyme by slowing or stopping the chemical reaction

  
• Competitive inhibitors


  Bind at the active site, creating competition with the substrate by blocking it from binding and stopping the chemical reaction
• Noncompetitive inhibitors


  Attach to another site on the enzyme called the allosteric site, changing the shape of the protein which changes the shape of the active site, causing the substrate to not fit

  
• Cofactors


  Small nonprotein molecules required for some enzymes to function properly
• If it ends with "-ase" it is an enzyme
• Slight changes can occur for the enzyme to align with the substrate

  
• Catalyst


  A substance that increases the rate of a chemical action without being consumed in the reaction
• Substrate


  The molecule or molecules an enzyme acts on
• Inhibitor


  Molecules that interfere with the functioning of an enzyme by slowing or stopping the chemical reaction

  
• A controlled experiment is a scientific investigation
• Types of tests in a controlled experiment

  • Control test/group
  • Experimental test/group
• Control test/group


  Generates data without treatment or manipulation, under normal/unchanged conditions, is the baseline/standard data
• Negative control


  Not exposed to the experimental treatment known to have an effect
• Positive control


  Exposed to a treatment that has a known effect but not exposed to the experimental treatment
• Experimental test/group


  Generates data under abnormal/unknown conditions, under treated/manipulated conditions
• Controlled variables


  Aspects of an experiment that could be changed but are not intentionally changed, important to help isolate and identify the impact of an intentional change/treatment
• Only variables known to have an impact should be considered as possible controlled variables
• Denaturation


  Enzyme denaturation is typically irreversible, and the catalytic ability of the enzyme is lost or severely decreased

  
• pH


  Measures the concentration of hydrogen ions in a solution, the more hydrogen ions the lower the pH = more acidic pH, small changes in pH values = large shifts in hydrogen ion concentration
• Changing pH from the optimal range


  Will slow or stop enzyme activity, may cause enzyme denaturation
• Initial increase in substrate concentration

  Increases reaction rate
• Substrate saturation


  Results in no further increase in reaction rate, remains constant
• Increased concentrations of products

  Decrease opportunity for addition of substrate, slowing reaction rate
• When environmental temperatures increase

  Reaction rates increase due to increased speed of molecular movement and increased frequency of enzyme-substrate collisions
• When environmental temperatures increase outside the optimum range


  Enzyme denaturation occurs
• When environmental temperatures decrease

  Reaction rate slows down due to decreased frequency of enzyme-substrate collisions (does not disrupt enzyme structure and no denaturation, catalyzing reactions stop at freezing temperatures)
• Denatured


  Not working, destroyed, damaged - the protein structure may change, losing its shape without losing its primary sequence
• Optimum temperatures


  The range in which enzyme-mediated reactions occur the fastest
• Buffer


  An aqueous solution that can resist significant changes in pH levels upon the addition of a small amount of acid or alkali
• Living things are not at equilibrium, there is a constant flow of materials in and out of the cell needing a constant input of energy
• The amount of energy we take in is greater than the energy given out
• We can recycle matter but not energy
• We lose energy for every metabolic pathway and chemical reaction in the form of heat
• Energy input is greater than energy output, so we need to manage energy efficiently through energy couplings
• Exergonic (exothermic) reactions


  Release heat (energy form)