Chapter 7 - Enzymes 

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• ^^To interact with the enzyme, the substrate must be able to fit into the active site.^^

  • ^^There must be suitable charges on the substrate if there are any charged R-groups on amino acids inside the active region of the enzyme.^^
  • An active site containing positively charged amino acids, for example, would resist any positively charged molecules, even if the molecule's form could fit in the active site of the enzyme.
  • Enzymes catalyze reactions more efficiently at specified enzyme-specific temperatures and pHs.

• If the temperature in the environment is too low, the rate of collisions between the enzyme and its substrate slows, and the process slows.

  • When the temperature is too high, the bonds that keep the enzyme together are broken.
  • Similarly, a pH that is too high might break enzyme linkages, resulting in a change in the enzyme's tertiary structure.

  Changes in an enzyme's ionic environment can potentially break bonds in the enzyme.

  • Denaturation is a change in the structure of an enzyme that can restrict the enzyme's capacity to catalyze chemical processes.
  • Denaturation can sometimes, but not always, be reversed when the environment returns to more ideal circumstances.

• Competitive inhibitors resemble substrates in form and compete with substrates for an enzyme's active site.

  • Noncompetitive (or allosteric) inhibitors bind to a different place on the enzyme than the active site (called the allosteric site).
  • ^^The noncompetitive inhibitor's binding.^^
  • The noncompetitive inhibitor's binding to the allosteric site modifies the structure of the enzyme, changing its activity.
  • ^^Because the noncompetitive inhibitor does not bind to the active site of the enzyme, increasing the concentration of substrate has no effect on the inhibitor's function.^^
  • Noncompetitive inhibitors can work as feedback mechanisms, modifying the pace of chemical processes in the cell in response to changing environmental variables.

• Life needs a steady supply of energy to run cellular operations and keep living systems in order.

  • To maintain life, the energy intake into the cell must be larger than the energy requirements of the cell.
  • Energy-releasing activities can be linked (or coupled) with energy-requiring ones.

• These linked reactions take place in a series of stages to allow for the regulated transfer of energy between molecules, resulting in greater efficiency.

  • While enzymes can reduce reaction activation energy, they cannot convert an endergonic reaction to an exergonic reaction.
  • Enzymes are incapable of converting an energetically unfavorable reaction into an energetically favorable one.
  • To initiate a chemical reaction, energy input is required to achieve a transition state.

• The activation energy (EA) is the difference in energy levels between the reactants and the reaction's transition state.

  • Higher activation energies cause slower chemical reactions; lower activation energies allow for quicker chemical reactions.
  • Enzymes accelerate chemical processes by decreasing the reaction's activation energy.
  • Exergonic reactions produce products with lower free energy levels than their reactants and are thus regarded energetically advantageous.

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