81 WJEC Biology AS Level - Marianne Izen - 2nd Edition (1.4 Enzymes And Biological Reactions) Flashcards
Describe non-competitive inhibition.
Non-competitive inhibitors bind to the enzyme at an ‘allosteric site’, i.e. a site other than the active site, so they do not compete with the substrate.
They affect bonds within the enzyme molecule and alter its overall shape, including that of the active site.
The substrate cannot bind with the active site, and no enzyme-substrate complexes form.
As the inhibitor concentration increases, the rate of reaction and final mass of product decrease.
As with competitive inhibitors, some non-competitive inhibitors bind reversibly and some irreversibly.
Give examples of non-competitive inhibitors
Examples of non-competitive inhibitors include heavy metal ions, e.g.
1. lead, Pb2+
2. arsenic, As3+.
Describe enzyme-substrate reactions In terms of molecular collisions.
With competitive inhibition, the greater the substrate concentration, in relation to Inhibitor, the greater the chance that the substrate and enzyme will collide.
When you have a reversible competitive inhibitor what is the end result?
When a competitive inhibitor is reversible, it can bind to and unbind from the active site.
When this happens, however much inhibitor is present, the mass of product formed ends up the same.
So eventually, all the substrate is used up.
Non-competitive inhibitor (Key-Term)
An atom, molecule or ion that reduces the rate of an enzyme-controlled reaction by binding to the enzyme at a position other than the active site, altering the shape of the active site and preventing the substrate from successfully binding to it.
Describe the mechanism of action of cyanide ion inhibitor.
The cyanide ion (CN-) is an Inhibitor of the respiratory enzyme, cytochrome oxidase.
It is unusual because, although it does not have the same shape as the substrate, it still binds at the active site and denatures it.
So its mechanism of inhibition is the same as non- competitive inhibitors.
Draw a graph to show the effect of reversible competitive inhibition on the mass of the product
Draw a diagram to show non-competitive inhibition
Draw a graph to show the effect of irreversible non-competitive inhibition on the mass of the product
