Lesson 9: Enzymes

Enzymes

: biological catalysts (speed up reactions but are not used up in the process) made of proteins

• lowers the activation energy (Ea)

Activation Energy

: the amount of energy (E) needed to start a reaction

Exergonic Reactions

: the release of E, reactants have more E than the products

Endergonic Reactions

: the storage of E, reactants have less E than the products

Enzyme Structure

• are specific and only breakdown the molecule they are designed for

Lock & Key Model

: only the substrate that perfectly fits in the active site will be broken down by the enzyme

Induced Fit Model

: enzymes are slightly flexible because they are proteins and can accommodate for a
  substrate that is not a perfect fit (but close)

Enzyme Inhibition

: when no substrate is present, the enzyme can be “turned off” using inhibitors

• Competitive Inhibitors (Inhibitor VS Substrate)
  : binds to the active site, blocking the active site from the substrate

• Noncompetitive Inhibitors

  : binds to the allosteric site, changing the active site’s shape so that the substrate no longer fits in it

Coenzyme

: an ion (not an enzyme) that is required to bind to an enzyme for it to function (e.g. Mg2+, Ca2+)

Factors that Affect an Enzymes Activity

• Temperature

  • Increase

    • particles move faster, increasing the # of collisions between the substrate and enzyme, increasing the reaction rate

    • if it is too high, the enzyme will denature (because it is a protein) and stops the reaction rate

  • Decrease

    • particles move slower, decreasing the # of collisions between the substrate and enzyme, decreasing the reaction rate

• pH

  • when outside of the enzymes optimal pH range, the enzyme denatures and stops the reaction rate

• Enzyme Concentration

  • higher enzyme concentration will increase the reaction rate until all of the substrate is broken down

• Substrate Concentration

  • higher substrate concentration will increase the reaction rate (because all of the substrate are grouped together) until all of the substrate is broken down

    • when all of the enzymes are “busy” the reaction rate will slow down