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BIOL 201
Elaine Power

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Enzymes  All enzymes are globular proteins and round in shape  They have the suffix "-ase"  Intracellular enzymes are found inside the cell  Extracellular enzymes act outside the cell (e.g. digestive enzymes)  Enzymes are catalysts → speed up chemical reactions o Reduce activation energy required to start a reaction between molecules o Substrates (reactants) are converted into products o Reaction may not take place in absence of enzymes (each enzyme has a specific catalytic action) o Enzymes catalyse a reaction at max. rate at an optimum state  Induced fit theory o Enzyme's shape changes when substrate binds to active site o Amino acids are moulded into a precise form to perform catalytic reaction effectively o Enzyme wraps around substrate to distort it o Forms an enzyme-substrate complex → fast reaction o E + S → ES → P + E  Enzyme is not used up in the reaction (unlike substrates) Changes in pH  Affect attraction between substrate and enzyme and therefore efficiency of conversion process  Ionic bonds can break and change shape / enzyme is denatured  Charges on amino acids can change, ES complex cannot form  Optimum pH o pH 7 for intracellular enzymes o Acidic range (pH 1-6) in the stomach for digestive enzymes (pepsin) o Alkaline range (pH 8-14) in oral cavities (amylase)  pH measures the conc. of H+ ions - higher conc. will give a lower pH Enzyme Conc. is proportional to rate of reaction, provided other conditions are constant. Straight line Substrate Conc. is proportional to rate of reaction until there are more substrates than enzymes present. Curve becomes constant. Increased Temperature  Increases speed of molecular movement → chances of molecular collisions → more ES complexes  At 0-42 °C rate of reaction is proportional to temp  Enzymes have optimum temp. for their action (varies between different enzymes)  Above ≈42°C, enzyme is denatured due to heavy vibration that break -H bonds o Shape is changed / active site can't be used anymore Decreased Temperature  Enzymes become less and
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