The Role of Enzymes (OCR A Level Biology)

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Enzymes as Catalysts

  • Enzymes are biological catalysts
    • ‘Biological’ because they function in living systems
    • ‘Catalysts’ because they speed up the rate of chemical reactions without being used up or undergoing permanent change

  • Enzymes are globular proteins with complex tertiary structures
    • Some are formed from a single polypeptide, whilst others are made up of two or more polypeptides and therefore have a quaternary structure

  • Metabolic pathways are controlled by enzymes in a biochemical cascade of reactions
    • Virtually every metabolic reaction within living organisms is catalysed by an enzyme
    • Enzymes are therefore essential for life to exist

Site of action of enzymes

  • All enzymes are proteins that are produced via the process of protein synthesis inside cells
  • Some enzymes remain inside cells, whilst others are secreted to work outside of cells
  • Enzymes can therefore be intracellular or extracellular, referring to whether they are active inside or outside the cell respectively
    • Intracellular enzymes are produced and function inside the cell
    • Extracellular enzymes are secreted by cells and catalyse reactions outside cells (eg. digestive enzymes in the gut)

Intracellular and Extracellular Enzymes Table

Enzymes table, downloadable AS & A Level Biology revision notes

Examiner Tip

Don't forget that enzymes are proteins, meaning that anything that could denature a protein and make it non-operational (such as extremes of heat, temperature, pH etc.) would also denature an enzyme. This is one reason why homeostasis (the maintaining of internal body conditions) is so important: to ensure that enzymes within the body can function properly, as they are essential to the survival of organisms.

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Alistair

Author: Alistair

Expertise: Biology & Environmental Systems and Societies

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.