Role of Enzymes (Edexcel IGCSE Biology)

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Enzymes as Biological Catalysts

  • Enzymes are proteins that act as biological catalysts to speed up the rate of a chemical reaction without being changed or used up in the reaction

  • They are biological because they are made in living cells

  • Enzymes are necessary to all living organisms as they maintain reaction speeds of all metabolic reactions 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

    • Often the products of one reaction are the reactants for another (and so on)

The mechanism of enzyme action

  • Enzymes are specific to one particular substrate(s) as the active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate

  • When the substrate moves into the enzyme’s active site they become known as the enzyme-substrate complex

  • After the reaction has occurred, the products leave the enzyme’s active site as they no longer fit it and it is free to take up another substrate

    • Step One: Enzymes and substrates randomly move about in solution

    • Step Two: When an enzyme and its complementary substrate randomly collide an enzyme-substrate complex forms, and the reaction occurs

    • Step Three: A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions

How enzymes work, IGCSE & GCSE Biology revision notes

How enzymes work

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Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.