Inhibitors & Signal Molecules

• • An inhibitor is a substance which slows down the rate of an enzyme

  controlled reaction.
• • An inhibitor may even be able to halt an enzyme controlled reaction.
• • A competitive inhibitor is a substance which is chemically similar to a

  substrate.
• • A competitive inhibitor will bind to the active site, physically blocking

  it.
• • A non competitive inhibitor is a substance which attaches itself to

  another area of the enzyme and changes the shape of the active

  site. This means the substrate cannot bind to the enzyme at the active site. The lock no longer fits the key.
• • *Non competitive inhibitors - regulation by changing the shape of the active site

  *Non competitive inhibitor does not combine directly with active site

  *Attaches to a non active (allosteric)site

  *Changes the shape of enzyme molecule

  Active site is altered indirectly so can't

  combine with substrate
• Competitive

  • Similar shape to substrate.

  • Bind to active site of enzyme.
• Non-competitive

  • Bind to the enzyme (not in the active site) and change its shape.

  • Substrate no longer fits.
• NON-COMPETITIVE

  The concentration of the inhibitor alone will control the degree of

  inhibition
• COMPETITIVE

  The concentration of the inhibitor and the concentration of the substrate control the degree of inhibition.
• A non competitive inhibitor will slow down the rate of the reaction and

  prevent the reaction from reaching the full potential reaction rate.

  Increasing the substrate concentration has no effect on the rate of

  reaction past the inhibited maximum.
• Metabolic pathways can be controlled by regulating enzyme activity using signal molecules or inhibitors. Signal molecules that originate in cell itself are intracellular signal molecules. Epinephrine is an example.