Enzymes, Biology


  • Biological catalysts à speed up chemical reactions in the body without being consumed in the process
    • Reduce the activation energy needed for reactants to reach the transition state

                        Don't change the ΔG

o   Heat can provide activation energy à denatures enzymes though =(

  • Substrate à the specific reactant that the enzyme acts on
  • Enzymes have a complex 3-D shape à means they are VERY specific on their substrate
  • Names of enzymes end in -ase
    • E.g. amylase catalyzes amylose into maltose
  • Active Sites
    • The site where the substrate binds
    • Small portion of the enzyme

                         Pocket/groove in the 3-D shape of the enzyme

o   As the substrate enters the active site

                          The functional groups in active site will react and cause the enzyme to change shape to accommodate the substrate

                           Known as the induced-fit model

  • Enzyme-substrate complex à enzyme with a substrate attached
  • Enzymes
    • Bend, stretch, change pH etc. to break or build bonds
    • Heat from the cell + enzyme activity = transition state
  • Enzyme activity
    • Increased with heat (too much denatures them though)
    • pH à can denature them (stomach enzymes work at pH of 2
    • some need cofactors

                  non-protein components (e.g. Zn2+ or Mn2+) that bind to active site or to substrate

o   coenzymes

                  organic non-protein cofactors (e.g. NAD+)

  • Inhibition of Enzymes
    • Competitive

                       Compete for active site

                       Reverse affect by increasing conc. of substrate

                 o   Non competitive

                     Attach to non-active-site site

  change shape of enzyme so the substrate doesn't fit or catalyzing action is reduced

  • Control of enzymes (either through reducing production of enzyme or through inhibition)
    • Allosteric sites à receptor sites a distance away from the active site

                   o    Activator

                         Stabilizes the active form of the enzyme

                   o   Allosteric Inhibitor

                           Stabilizes the inactive form of the enzyme

  • Feedback inhibition
    • A product formed later in a series of chemical reactions allosterically inhibits an enzyme working earlier on in the process

                         Enzyme is inhibited à Less products formed à less inhibitors à enzyme activity goes up à more products (inhibitors) formed

                 o   E.g. threonine is catalyzed into isoleucine

                          Isoleucine inhibits the first enzyme that would act on threonine

  • Milk à cheese
  • Creating wine
  • Brewing beer
  • Starch à ethanol
  • Removing stains


Posted Date: 8/20/2012 5:31:27 PM | Location : United States

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