Biology: Chapter 3: Enzymes: Inhibitors

Biology: Chapter 3: Enzymes: Inhibitors

• Enzyme inhibitors reduce the rate of reaction by interfering with the enzyme in some way.
• Can be temporary or permanent.

Competitive inhibitors

• Another molecule, with a similar structure to the type of substrate the enzyme catalyses, binds with the enzyme, inhibiting it's function for other substrates. 
• The competitive inhibitor therefore creates competition for the substrate, lowering the rate of reaction as the substrates have less enzymes to bind to. 
• Rate of reaction depends on the concentration of substrate and inhibitor. More inhibitors - lower rate of reaction.
• Usually temporary as the inhibitor will leave the enzyme after a certain time.
• Example: Ethylene glycol is used as antifreeze, and can sometimes be drunk accidentally. In the body it is quickly converted to oxalic acid, which causes permanent kidney damage. However, when the person is given ethanol, ethanol acts as a competitive inhibitor, slowing down the reaction of ethylene glycol long enough for it to be excreted. 

Non-competitive inhibitors

• Molecule that binds to another part of the enzyme, called the Allosteric site, affecting the bonding in the 3D shape of the enzyme molecule and altering the shape and shape of the active site so substrates cannot bind to the enzyme. 
• Enzyme will be blocked no matter how much substrate is present, which is why it is called a non-competitive inhibitor.
• Usually permanent, denaturing the enzyme they exhibit, which can be lethal.
  
• However, temporary non-competitive inhibitors are essential for metabolic reactions. This is because reactions need to tightly controlled as so they don't 'run wild'. 
• Temporary non-competitive inhibitors allow products to be produced in specific amounts.
• In multiple sclerosis, enzyme rate is not controlled and the immune system allows the enzymes to attack the nerves, resulting in paralysis.
• One common way of controlling metabolic reaction is using the end product of a metabolic pathway as a non-competitive inhibitor. 
• Metabolic pathway: Process composed of many different reactions, each catalysed by a different enzyme.
• This means the process controls itself, as the more product is produced, the more enzymes get inhibited, meaning less substrate binding. But once the end-product is needed, it can detach from the enzyme, allowing it to function again.