2.6 Enzyme action

2.6 Enzyme action

1. Globular proteins as CATALYSTS

   • Catalysts alter the rate of a chemical reaction without undergoing permanent changes themselves
     • Can be reused repeatedly = effective in small amounts
     • Specific for a particular chemical reaction

2. LOWERING THE ACTIVATION ENERGY

   • For a reaction to happen:
     • Reactant molecules must collide with sufficient energy to alter atom arrangement to form products
     • Energy of products less than energy of reactants
     • Activation energy needed to start reaction = the minimum amount of energy needed to activate the reaction
   • Enzymes increase rate of chemical reaction by lowering the activation energy

3. ENZYME STRUCTURE

   • Globular proteins = specific 3D shape due to sequence of amino acids (primary)
   • ACTIVE SITE = small functional region of enzymes
     • Made up of relatively small number of amino acids
   • Substrate fits into active site to form ENZYME-SUBSTRATE COMPLEX
     • Substrate molecule held within active site by BONDS formed between certain amino acids of active site and groups on substrate

4. LOCK AND KEY MODEL

   • Substrate has a complementary shape to the active site
     • Shape of substrate exactly fits active site of enzyme
   • Substrate has specific shape and so will only fit the active site of one particular enzyme
     • Enzymes are specific in the reactions they catalyse
   • LIMITATIONS
     • Model considers enzyme as a rigid structure
       • However, other molecules can bind to enzymes at sites other than active site
         • Alter activity of enzyme
           • Shape of enzyme can be altered
             • Enzyme structure is actually flexible

5. INDUCED FIT MODEL

   • Enzyme has certain general shape that alters in presence of substrate to fit the shape of substrate
     • Enzyme is flexible = changes shape
       • Change of shape puts strain on substrate molecule
         • Strain distorts particular bond = activation energy needed to break the bond is lowered
   • STRENGTHS
     • Explains how other molecules can affect enzyme activity
     • Explains how activation energy is lowered

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