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Key Concepts

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Examples of Enzymes

Note that the names of enzymes end with ase and are related to the reaction they catalyse:

Enzyme Catalysed Reaction
amylase hydrolysis of starch (amylose)
maltase hydrolysis of maltose
invertase (sucrase) hydrolysis of sucrose
succinate dehydrogenase dehydrogenation of succinic acid
ascorbic acid oxidase oxidation of ascorbic acid
protease hydrolysis of proteins
polymerase polymerisation reaction
reductase reduction reaction

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Enzyme Structure

Enzymes are proteins that act as catalysts for biological reactions.

Primary Structure :

Secondary Structure :

Tertiary Structure :

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How Enzymes Work

Lock and Key Model

Induced Fit Model

enzyme + substrate → enzyme-substrate complex → enzyme-product complex → enzyme + product

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Conditions For Enzyme Function


Enzymes are highly sensitive to changes in temperature.

In humans, most enzymes function best at body temperature (approximately 37oC).

In general, heating a reaction mixture speeds up the rate of reaction by increasing the number of successful collisions between reactant molecules. This is shown on the graph to the right before the optimum temperature for enzyme activity is reached.

If the temperature of the reaction is raised too high past the optimum temperature, the reaction rate decreases as the enzyme becomes denatured and loses its ability to function as a catalyst for the reaction.


Some enzymes can only act within a certain pH range.

Outside this pH range the enzyme may become denatured, lose its tertiary structure, and therfore lose its ability to function as a catalyst for the reaction.