M10. Enzymes increase reaction rates by lowering activation energy.

Student Outcome: M10.1

Understand that reactions require an initial input of energy to proceed.

The way enzymes work can also be shown by considering the energy changes that take place during a chemical reaction. We shall consider a reaction where the product has a lower energy than the substrate, so the substrate naturally turns into product . Before it can change into product, the substrate must overcome an "energy barrier" called the activation energy (EA).

The larger the activation energy, the slower the reaction will be because only a few substrate molecules will by chance have sufficient energy to overcome the activation energy barrier. Imagine pushing boulders over a hump before they can roll down hill, and you have the idea.

Source: http://www.biologymad.com/master.html?http://www.biologymad.com/Enzymes/enzymes.htm

Student Outcome: M10.2

Describe how enzymes catalyse biological reactions by lowering the input of energy required to initiate the reaction.

Most physiological reactions have large activation energies, so they simply don't happen on a useful time scale. Enzymes dramatically reduce the activation energy of a reaction, so that most molecules can easily get over the activation energy barrier and quickly turn into product.

For example, for the catalase reaction (2H2O2 -> 2H2O + O2) the activation energy is 86 kJ mol-1 with no catalyst, 62 kJ mol-1 with an inorganic catalyst of iron filings, and just 1 kJ mol-1 in the presence of the enzyme catalase.

Source: As above.

Video about activation energy.

And just because I can, here is a plasticine version of enzyme action:

Just for something completely different! How about some excerpts from The Manga Guide to Molecular Biology - how enzymes work in the liver!

Interested? You can get the book here (at Amazon)