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CSEC Biology: Enzymes

Enzymes are biological catalysts which speed up the rate at which chemical reactions occur and can be recovered, unchanged after the reaction has been completed. They do this by lowering the activation energy.

Enzymes are necessary for life because without them, reactions would occur too slowly to sustain life.

Enzymes are mostly proteins that bind to a specific molecule or substance known as its substrate. The region where an enzyme binds to its substrate is known as its active site, which is specifically suited to only bind to its substrate and nothing else.

The enzyme can either split its substrate into two products or join it with another substrate to form a larger molecule. The product(s) is/are released, and the enzyme remains the same.

This process of substrate binding to enzyme is summarized like this:



You are probably already familiar with some of the enzymes in your digestive system, like amylase, which breaks down starch into maltose.


There are 5 main properties of enzymes:

Catalytic Property- This basically means that they are biological catalysts, i.e. they speed up chemical reactions without experiencing a permanent change.


Specificity- As stated earlier, enzymes are very specific in their action. A certain enzyme will only act on a specific substrate and will only catalyze a specific reaction.


Reversibility- Most enzymes catalyze reversible reactions


Sensitivity to Temperature- The rate at which enzymes catalyze reactions is affected temperature. At higher temperatures, enzymes are denatured, that is, the shape of the enzyme molecule is changed, causing it to become inactivated. The active site of the enzyme is changed and is no longer able to bind to its substrate. At lower temperatures, the rate of enzyme activity is reduced because (as discussed in a previous physics post) the kinetic energy of the particles would be lessened. This makes it so that the substrate would collide far less frequently with the enzyme, therefore reducing the rate of reaction. Enzymes work best at a particular temperature known as the optimum temperature.

This is around 37°C for human enzymes.

As the temperature increases past the optimum temperature, enzyme activity decreases steeply as the enzymes are denatured.


Sensitivity to pH- Enzymes will function best at a particular pH known as the optimum pH. This is a pH of 7 for most enzymes. Extremes of alkalinity or acidity will denature most enzymes.


You should also know that some vitamins help enzyme activity, and certain compounds (like some poisons) are enzyme inhibitors that slow down enzyme activity.


Additional Reading/Sources

BioNinja Site

Properties of Enzymes

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