Enzymes
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ENZYMES. Enzymes An enzyme is a protein catalyst. Enzymes facilitate reactions without being used up. Lower the activation energy of a reaction. Generally, energy added to a reaction to speed it up is in the form of heat. This is not good for cells – Why?

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Enzymes
ENZYMES

  • Enzymes

  • An enzyme is a protein catalyst.

  • Enzymes facilitate reactions without being used up.

    • Lower the activation energy of a reaction.

    • Generally, energy added to a reaction to speed it up is in the form of heat.

      • This is not good for cells – Why?

  • Because of this, enzymes are critical


Enzymes


Enzymes

  • Enzymes act on a therefore, they will not affect equilibrium nor will they cause a reaction that would not normally occur spontaneously to do so.substrate (reactant).

    • The substrate binds to a particular site on an enzyme that is very specific for it.

      • Most enzymes will not even bind to isomers of reactants.

  • Enzymes are generally named for their substrate and end in –ase.

    • eg) amylase binds to amylose, maltase binds to maltose.

  • The substrate binds to a very small portion of the enzyme.

    • The active site

  • Usually a pocket or groove in the quaternary structure of the enzyme.


Enzymes

  • As the substrate nears the functional groups of the amino acids in the enzyme protein, the enzyme changes it shape to better accommodate the substrate.

    • Known as the induced-fit model of enzyme-substrate interaction.

    • The attachment of the substrate to the active site creates the enzyme-substrate complex.

  • Essentially, the enzyme stresses the bonds of the substrate that would normally break in a reaction.

    • The heat generated by the cell, in conjunction with the stressed bonds brings the substrate to its transition state.


Enzymes

  • Some enzymes require acids in the enzyme protein, the enzyme changes it shape to better accommodate the substrate.cofactors for them to work properly.

    • Usually either inorganic substances or organic coenzymes

      • Many functions, including shuttling of molecules from one enzyme to another.

  • VISIT THE SITE BELOW FOR ANIMATION

  • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html


Enzyme inhibition
ENZYME INHIBITION acids in the enzyme protein, the enzyme changes it shape to better accommodate the substrate.

  • Some compounds reduce the efficacy of an enzyme. These are usually broken down into two groups.

    • Competitive inhibitors

      • Similar enough to the substrate to bind to the active site and block the normal substrate from binding.

      • Can be overcome by increasing the concentration of substrate.

    • Noncompetitive inhibitors

      • Do not compete for the active site.

      • Bind to another site on the enzyme and change the shape of the entire molecule.

  • The enzyme then loses its affinity for the substrate.


Enzyme inhibition1
ENZYME INHIBITION acids in the enzyme protein, the enzyme changes it shape to better accommodate the substrate.


Enzymes

  • Cells must regulate enzyme activity to coordinate cellular activity.

  • Can be accomplished two ways:

    • Restricting production of enzymes

    • Inhibiting action of enzymes

      • Some enzymes have allosteric sites that do not relate to substrate activity.

      • Binding an activator to an allosteric site allows the enzyme to function properly.

  • Binding an allosteric inhibitor stabilizes the inactive form of the enzyme


Feedback inhibition
FEEDBACK INHIBITION activity.

  • Feedback Inhibition

  • Used by cells to control metabolic pathways involving a sequence of reactions.

  • A product formed later in the series acts as an allosteric inhibitor to an enzyme earlier in the series.

    • As the product is used up, the inhibitor concentration decreases and the enzyme once again becomes active.

    • The sequence restarts, resulting in more product which then inhibits the earlier enzyme.