Enzymes are protein molecules that help chemical reactions in living organisms to take place. The term enzyme has a specific meaning: an enzyme is a biological catalyst that speeds up the rate of a chemical reaction without being used up in the chemical reaction itself. Let us analyse this definition in greater detail.
Biological: Enzymes are protein molecules which are made of long chains of amino acids. These fold into unique three-dimensional structures with a region known as an active site where reactions take place.
Catalyst: Enzymes speed up chemical reactions without being used up in the reaction themselves. All chemical reactions require a certain minimum amount of energy to take place. This energy is known as the free energy of activation. Enzymes lower the energy of activation thus speeding up chemical reactions (see figure below).
Enzymes are not consumed by the reactions they catalyse: they do not alter the equilibrium of reactions, thus they catalyse both forward and reverse reactions. The direction in which a reaction proceeds is determined by concentration of the substrates and the products of the reactions.
Enzymes may be involved in reactions that break down or build up molecules. The breakdown reactions are known as catabolic reactions. The building up reactions are known as anabolic reactions.
The ‘lock and key’ model of enzyme action
Enzymes are highly specific regarding the reactions they catalyse. The specificity depends on the bonds formed between the active site of an enzymes and its substrate. Active sites have a specific shape that allows binding of a very specific substrate. The highly specific nature of the enzyme-substrate binding has been compared to a “lock and key” with the enzyme as the ‘lock’ and the substrate as the ‘key’ (see figure below). The substrate binds the active site to form an enzyme-substrate complex. The reaction takes place, then the product leaves the active site as it no longer fits the ‘lock’ in the same way as the substrate did. The enzyme remains unchanged.
Investigation: Investigating How Biological Washing Powders Work
To test how enzymes in biological washing powders work
- two soft boiled eggs (hard boiled eggs contain denatured proteins that do not cause stains)
- two beakers
- biological washing powder (with enzymes)
- non-biological washing powder (older type of washing powder)
- two measuring spoons
- Label 3 beakers ‘Bio’, ‘Non-Bio’ and ‘control’ which will contain biological washing powder, non-biological washing powder and water (negative control) respectively.
- In the beaker labelled ‘Bio’ dissolve 5 g of biological washing powder in 30 ml water.
- In the beaker labelled ‘Non-Bio’ dissolve 5 g of non-biological washing powder in 30 ml water.
- Pour 30 ml of tap water into the control beaker.
- Scoop out a small amount of egg yolk.
- Place a teaspoon with the egg yolk in each of the beakers.
- Leave the spoons in the beakers for 1 to 2 hours.
- Observe your results.
- Write down your observations.
- Suggest a reason for your observations.
- Write a conclusion for the investigation.
Enzymes in Everyday Life
The properties of enzymes to control reactions have been widely used for commercial purposes. Examples of some of these uses are listed below:
- Biological washing powders contain enzymes such as lipases (breaks down lipids) and proteases (breaks down protein), which assist in the breakdown of stains caused by foods, blood, fat or grease. These biological washing powders save energy as they are effective at low temperatures.
- Meat tenderisers contain enzymes which are obtained from fruits such as papaya or pineapple. When used in meat tenderisers these enzymes soften the meat.
- Lactose-free milk is manufactured primarily for people who are lactose intolerant. Lactose intolerant individuals lack the enzyme lactase that digests lactose (milk sugar). Lactose is pre-digested by adding lactase to the milk.