Enzymes (Cambridge (CIE) O Level Biology): Revision Note

What Are Enzymes?

• Enzymes are biological catalysts

• This is because they are:

  • Catalysts that speed up the rate of a chemical reaction without being changed or used up in the reaction

  • Made from the biological molecule protein

• They are necessary to all living organisms as they maintain reaction speeds of all metabolic reactions (all the reactions that keep an organism alive) at a rate that can sustain life

  • For example, if we did not produce digestive enzymes, it would take around 2 - 3 weeks to digest one meal; with enzymes, it takes around 4 hours

How Do Enzymes Work?

• The enzyme is made from protein that is folded into a very specific 3D shape

• Part of this 3D shape is a section of the enzyme called the active site

• The active site is the section of the enzyme that binds to the substrate (the reactant)

• When the enzyme binds to the substrate it is called the enzyme-substrate complex

The formation of the enzyme-substrate complex diagram

The enzyme-substrate complex forms when the substrate binds to the active site of the enzyme

• The product is made from the substrate(s) and is released

• After the product is released the enzyme is free to bind to a new substrate and repeat the reaction again

Diagram showing how enzymes work

Enzymes act as biological catalysts