• 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

• As well as amylase (which hydrolyses starch into maltose), another example of an extracellular digestive enzyme that is secreted by the pancreas and enters the small intestine is?trypsin, which breaks?proteins?down into?peptides?and?amino acids
• In fact, some organisms can only feed using a form of?extracellular digestion?in which the digestive enzymes are actually secreted?outside?of their?bodies
  • For example, the?hyphae?of?fungi?secrete the necessary enzymes?directly?onto the food?they are consuming (e.g. wood) so that the food is digested into smaller, simple molecules that the fungi can then?absorb?through the walls of the hyphae