Enzymes

• Enzyme

  Proteins that catalyse the different processes that take place in living organisms to allow them to survive
• Catalysts


  Enzymes are called biological catalysts because they speed up reactions in living organisms
• Enzyme catalysis

  • Rubisco in plant cells catalyses the fixation of CO2 in photosynthesis
  • Amylase in saliva catalyses the breakdown of starch to sugars
• Enzymes

  • They speed up reactions that affect the organism on the cellular and individual level
  • They catalyse photosynthesis, the products of which are used around the plant on the organismal level to grow roots and shoots
  • They speed up reactions that affect both structure and function (e.g. production of collagen, respiration)
• Lock and key model


  The model proposes that the enzyme and substrate fit together perfectly, with the substrate as a key fitting into a lock (enzyme)
• Induced fit model


  The model states that as an enzyme and substrate come together, their interactions cause a small shift in the enzyme's structure, allowing the enzyme-substrate complex to form and catalyse a reaction
• Active site

  Every enzyme only catalyses one specific reaction, and has a specific active site that is complementary to the specific substrate
• Environmental factors

  • Changes to the tertiary structure of an enzyme through changing the pH or temperature will affect how fast reactions are catalysed
  • Increasing temperature increases the kinetic energy of molecules, increasing the chance of collisions between enzyme and substrate, so increasing the rate of reaction
  • The temperature coefficient (Q10) measures the change in the rate of reaction when temperature increases by 10 degrees Celsius, usually around 2
• Denatured enzymes


  Increasing or decreasing the temperature or pH outside of an optimal range can affect chemical bonds within the active site, causing the enzyme to not work as well
• Increasing substrate concentration

  Increases the initial rate of reaction, but when all enzyme molecules are engaged in enzyme-substrate complexes, the rate cannot increase any further and plateaus
• Increasing enzyme concentration

  Increases the number of enzyme molecules available to catalyse the substrate in a given amount of time
• Coenzymes


  Organic molecules that bind to enzymes to increase the speed of reaction, and are a type of cofactor
• Cofactors


  Small molecules that increase the activity of enzymes by binding to them and causing a conformational change
• Prosthetic groups

  Inorganic molecules that permanently bind to enzymes to form part of the structure and increase the speed of reaction, and are a type of cofactor
• Competitive inhibitors


  Chemicals similar in shape to the usual substrate that affect the active site directly, blocking access for the formation of enzyme-substrate complexes
• Non-competitive inhibitors


  Affect another part of the enzyme molecule, causing a change to the shape of the active site so it is no longer complementary to the substrate molecules
• Zymogen

  An inactive precursor to an enzyme that needs to be cleaved to be activated, a way of regulating enzyme activity