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Enzymes

Enzymes. Important protein complexes. Background. Activation Energy: the energy needed to start non-spontaneous chemical reactions Catalyst: a compound that decreases activation energy and speeds the reaction. Catalysts are not consumed in the reaction so they are reuseable. Enzymes.

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Enzymes

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  1. Enzymes Important protein complexes

  2. Background • Activation Energy: the energy needed to start non-spontaneous chemical reactions • Catalyst: a compound that decreases activation energy and speeds the reaction. • Catalysts are not consumed in the reaction so they arereuseable

  3. Enzymes • Are biological catalysts • Belong to a class of proteins • Speed up reactions by decreasing the activation energy barrier • Each enzyme is substrate specific (molecular recognition)

  4. Induced-Fit Model of Enzyme Reaction • The active site is a restricted area (often a surface groove) to which the substrates bind. • The active site is only a small fraction of the enzyme and contains amino acids with active side chains • An enzyme’s specificity is due to compatible fit between the shape of the substrate and the active site (governed by 3° structure) • Bonding involves non-permanent bonds (H-bonds, Ionic bonds, etc.)

  5. Induced-Fit model • The substrate(s) entering the active site induces a deformation (slight change in shape) so that the functional groups in the active site fit more closely around the substrate(s) • Bonds are formed or broken because the flexing weakens and strains the chemical bonds in the substrate(s) making it more reactive • Bonds may be moved to a more stable arrangement

  6. http://www.cas.muohio.edu/~wilsonkg/old/gene2005/syllabus_F03_23.jpghttp://www.cas.muohio.edu/~wilsonkg/old/gene2005/syllabus_F03_23.jpg

  7. Lock and Key Model • The lock is the enzyme and the key is the substrate • Only the correctly sized key (substrate) fits into the key hole (active site) of the lock (enzyme). • Smaller keys, larger keys, or incorrectly positioned teeth on keys (incorrectly shaped or sized substrate molecules) do not fit into the lock (enzyme). • Only the correctly shaped key opens a particular lock.

  8. Factors That Affect Enzyme Activity I. Environmental conditions: • Optimal temperature allows the greatest number of molecular collisions without denaturing • Optimal pH (usually 6-8) high acid denatures most enzymes (except pepsin at pH 2 in the stomach) • Salt usually dissociates in aqueous solutions to form ions. Inorganic ions interfere with the 3° structure (ionic bonds)

  9. Factors That Affect Enzyme Activity II. Cofactors: Many enzymes need non-protein helpers for catalytic activity (bind to active site) • Some are inorganic (metals like Zn, Cu, or Fe) • Some are organic (coenzymes that are made from vitamins) III. Inhibitors: prevent enzyme activity • Competitive inhibitors resemble the substrate and block active site • Non-competitive inhibitors bind outside the active site and change the enzymes shape so the active site is non-receptive • Some inhibitors are harmful to the organism (DDT, antibiotics) • Others are necessary for metabolic control

  10. Enzyme Function • http://www.youtube.com/watch?v=PILzvT3spCQ

  11. http://www.emc.maricopa.edu/faculty/farabee/BIOBK/biobookenzym.htmlhttp://www.emc.maricopa.edu/faculty/farabee/BIOBK/biobookenzym.html

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