enzymes

• Textbook: Chapters 5.4, 5.5, 5.6


  Feb 14 & 16, 2024
• Unit 2: Energy and Metabolism (4 Weeks)

  • Energy flow in biochemical reactions and cellular processes
  • Enzymes
  • Photosynthesis
  • Glycolysis and fermentation
  • Cellular respiration
• What is an enzyme and what do they do?
• What are some unique characteristics of enzymes?
• How do enzymes work?
• What environmental conditions do enzymes work best at?
• How are enzymes regulated (controlled)?
• How ordered metabolic pathways arise

  1. Cells couple reactions together, powering energy-requiring endergonic reactions with energy-releasing exergonic ones

  2. Cells make energy-carrier molecules that capture energy from exergonic reactions and transport it to endergonic ones

  3. Cells regulate chemical reactions using special proteins called enzymes
• Enzymes


  Highly efficient biological catalysts
• Enzymes


  • They speed up chemical reactions by lowering the activation energy
  • They can only speed up reactions that are possible
  • They aren't used up or permanently modified by the reactions they catalyze
• Enzymes


  • They are specific for a very small number of reactants (substrates)
  • Enzymatic activity is often regulated (controlled) by the cell
• Active site


  The pocket in the tertiary or quaternary structure of an enzyme where the reaction will take place
• How an enzyme catalyzes a reaction


  1. The substrate or substrates enter the active site

  2. The enzyme changes shape, which either forces the substrates close together or puts stress on the bonds of a substrate, promoting a reaction

  3. The product or products no longer fit in the active site and are released. The enzyme returns to its original shape
• Enzymes are much more efficient than their chemical catalyst counterparts
• Enzyme function relies on having the correct tertiary structure
• Environmental conditions affect enzyme tertiary structure and therefore function
• Mechanisms by which the cell can regulate its enzymes

  • Cells regulate the synthesis of enzymes depending on whether that enzyme is needed or not
  • Cells synthesize some enzymes in an inactive form
  • Enzymatic activity can be increased or decreased by allosteric regulation
  • Enzymes can be inhibited by competitive inhibition
• Enzyme regulation #1: Synthesis based on need


  Some enzymes are only synthesized when they are needed
• Enzyme regulation #2: Synthesis of inactive enzymes


  Some enzymes are made in an inactive form and will only be activated once they are in the correct environmental conditions
• Enzyme regulation #3: Allosteric regulation


  Some enzymes have places other than the active site where certain molecules can bind to them, causing the enzyme to change shape
• Allosteric activation


  When binding of a molecule causes the enzyme to change shape so that its active site does have the correct shape
• Allosteric (non-competitive) inhibition


  When binding of a molecule causes the enzyme to lose the correct active site shape
• Feedback inhibition


  A form of allosteric inhibition where the product of a metabolic pathway inhibits one of the first enzymes in the pathway
• Enzyme regulation #4: Competitive inhibition


  Some molecules can mimic the normal substrate of the enzyme and bind to the active site instead, blocking the active site