Biology: what is competitive inhibition?

Tutoring biology, you might be asked about competitive inhibition. The tutor explains it.

In my November 25, 2013 post, I explain what an enzyme is. Simply put, an enzyme is a biological catalyst that the body uses to speed up a chemical process. An enzyme is not consumed by the reaction, but works alongside it, so can be reused.

Competitive inhibition reduces the effectiveness of an enzyme, possibly with fatality. Along with some preliminary ideas, here’s how it happens:

  1. The molecule an enzyme works on is called the substrate. The enzyme speeds the transformation of the substrate into what the body needs.
  2. The substrate, normally, binds to the enzyme at what’s called the enzyme’s active site in order for the enzyme to work on it.
  3. Therefore, let’s imagine that enzyme E works on substrate S to make necessary molecule M.
  4. Once S transforms to M, enzyme E is released; E is not attracted to M.
  5. Competitive inhibition starts with the arrival of a different substrate, ¬S, that is
    • attractive to enzyme E at the active site
    • not transformable to the necessary molecule M
    • will not become M, so will not release E (or not very quickly, anyway)
  6. The result is that E becomes busy with ¬S, so its active site is inaccessible to S.
  7. Without access to the active site of E, S can’t transform into M.
  8. The body needs M; without it, health consequences, possibly even death, will manifest.

Such is the mechanism of competitive inhibition. Some poisons are competitive inhibitors.


Biology 12 Module 1. Open School BC, 2007.

Mader, Sylvia. Inquiry into Life, 11th ed. Toronto: McGraw Hill, 2006.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Tagged with: , , , ,

Leave a Reply