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Enzymes | Cells | Biology | FuseSchool

Enzymes are really important proteins that speed up the rates of reactions such as in photosynthesis, respiration and protein synthesis.

The enzymes and substrates are always moving, and occasionally they collide at the right speed and orientation so that the substrate fits into the enzyme at the active site. Collision theory dictates that collisions must occur with sufficient energy and in a specific orientation for a reaction to occur.

Enzymes are specialised; their active site matches the shape of the specific substrate that they react with. The enzyme and the substrate fit together using a lock and key mechanism. Once the substrate is in the active site, the reaction takes place. The required product is produced and the enzyme releases itself and carries on moving around.

The enzyme could be: protease, which breaks down proteins into amino acids; carbohydrase which breaks down carbohydrates into glucose; or lipase which breaks down fats into fatty acids and glycerols.

Hydrogen peroxide is often formed as a result of reactions in cells, and if it is left to build up it is harmful. Luckily, we have catalase enzymes that are really fast. They break the hydrogen peroxide down into the harmless water and oxygen.

Equally, enzymes can help build up molecules like this… but the process is still exactly the same.

Whilst enzymes do fantastic things, they are sensitive. Each enzyme has optimum conditions under which it works best. Firstly, there needs to be enough substrate around - they need a high enough substrate concentration for the reaction that they catalyse. If there is too little substrate, then the rate of reaction is slowed. Sometimes, if there is too much product around, the reaction slows because the enzymes and substrates have less chance of bumping into each other. So the product needs to be removed for a higher rate of reaction.

Enzymes also have optimum pH and temperature conditions. Up to a point, an increase in temperature causes an increased rate of reaction because there is more heat energy. More energy means more collisions. However, above a certain temperature the rate drops off due to denaturing. We will look at the effect of pH and temperature on enzymes in our video ‘Denaturation of Enzymes’. The pH and temperature optimum conditions are specific to the conditions in which they work in; an enzyme that works in the stomach, for example, would have a more acidic optimum pH.

And of course, there need to be enough enzymes around for the rate of reaction to be optimised.

So we know that enzymes and substrates fit together at the active site and form a ‘lock and key’ mechanism. The enzyme then releases the product and can be reused again. They are sensitive to temperature and pH, and there needs to be sufficient enzyme and substrate concentrations for reactions to occur.

Enzymes not only control all kinds of reactions such as in photosynthesis, respiration, digestion and protein synthesis, but we also make use of them in day to day life. Protease and lipase enzymes are used in biological washing powders to remove proteins and fats from stains in our clothes. We also use enzymes in our food and drink industries; pectinase is used to break down the cells in fruit when making fruit juice so that more juice is released.


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