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SURENDRANATH COLLEGE
The Mechanism of enzyme action
Enzyme changes shape
slightly as substrate binds
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Substrate
Via site /
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active site of enzyme complex complex active site of enzyme
INDUCED FIT MODEL In 1959, Koshland suggested a modification to the ‘Lock and Key’ hypothesis which is known as ‘Induced fit’ hypothesis. Working from evidence that suggested that some enzymes and their active site are more flexible. To this, he proposed that the active site can modify its shape as the substrate interact with the enzyme. The amino acids which make up the active site are moulded into precise shape which enable the enzyme to perform its catalytic function most efficiently. For instance, a suitable analogy to describe Induced fit model would be that of a hand changing the shape of the glove as the individual put on the glove. Therefore in this case, glove is the active site of enzyme and the hand is substrate. However, in some cases, the substrate molecules changes slightly as it enters the active site before bindinG
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Product
Reaction progress
HOW ENZYME CATALYSE A REACTION? • Enzymes are catalyst that accelerate the rate of biochemical reaction by decreasing the energy of activation. • Every chemical reaction have energy barrier that must be crossed by the reactant molecules in order to convert itself into the product. • The amount of energy supplied to reactant molecules in order to cross the energy barrier to from product is known as Energy of activation. • If energy of activation is higher, rate of reaction is slower and if it is lower, the rate of reaction is faster. • The role of enzyme in biochemical reaction is to reduce the amount of energy of activation such that the rate of reaction increases. • During enzyme catalysis, active site of enzyme binds with substrate molecules to form Enzyme-substrate (ES) complex. During this binding some binding energy is released which is utilized to activate the substrate (reactant) molecules to form product. Thus the requirement of the amount of activation energy is decreased such that rate of reaction increases. The amount of activation decrease is equal to the amount of binding energy released during binding of enzyme and substrate. FACTORS AFFECTING THE RATE OF ENZYME REACTIONS TEMPERATURE Temperature: Raising temperature generally speeds up a reaction, and lowering temperature slows down a reaction. However, extreme high temperatures can cause an enzyme to lose its shape (denature) and stop working. PH pH: Each enzyme has an optimum pH range. Changing the pH outside of this range will slow enzyme activity. Extreme pH values can cause enzymes to denature.
