Introduction to Enzymes

Enzymes exist in both plant and animal cells. They aid in several reactions necessary for growth and survival in both plants and animals.


Enzymes are known as biological catalysts. A catalyst is a substance that alters the rate of a chemical reaction without being chemically changed itself. They are referred to as biological catalyst because enzymes are protein molecules made by living organisms. Enzymes catalyse the breakdown of a substrate into product(s). The substrate is simply the substance that is being broken down while the product, as the name suggests, is the end result.


In a typical human cell there are several thousand enzymes present. Without enzymes in a living organisms body several reactions would occur too slow to sustain life.


All enzymes are named. The name an enzyme receives is often done according to the substrate whose breakdown is being catalysed. For example, lipases catalyse the breakdown of lipids, and enzymes that catalyse the breakdown of carbohydrates are called carbohydrases.


Properties of Enzymes


-Enzymes are protein in nature. Being protein in nature they are made up of amino acids.

-Enzymes are biological catalysts. They speed up certain reactions in order to sustain life. The presence of enzymes does not alter the nature of the end product of the reaction.

-Enzymes are very efficient and specific. A very small amount of a catalyst brings about the change in a large amount of substrate. An enzyme will generally catalyze only a single reaction or a specific type of reaction. That’s how specific they are. E.g. catalase will only catalyze the decomposition of hydrogen peroxide.


-Enzyme activity is affected by factors such as pH, temperature, substrate concentration and enzyme concentration.


-pH refers to how acidic or alkaline a solution is. Some enzymes work best in acidic conditions (low pH), while other enzymes work best in alkaline conditions (high pH).


-Temperature can greatly affect the activity of enzymes; there is often a maximum and minimum temperature at which enzymes are active. Above and below these temperatures, respectively, there may be very little or no enzyme activity. Additionally, there is often a temperature which produces maximum enzyme activity. This is referred to as the optimum temperature.

Heat promotes molecular motion and thus increases the rate of reaction. However since enzymes are protein structures, they may be denatured by excessive heat. As such, there is an optimal temperature at which any increase in temperature will result in a reduction in the rate of reaction.


-The substrate concentration refers to the amount of substance that needs to be broken down. The enzyme concentration refers to the quantity of enzyme available to participate in reactions. If there is a low enzyme substrate concentration, the reaction rate will be quite slow. However, if there is a high enzyme substrate concentration, the reaction rate will increase as less time will be needed for conversion of the substrate(s) into product(s).

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