Enzymes
Enzymes are biological catalysts that speed up chemical reactions in living organisms. There are more
than five hundred different enzymes in every cell of the body, each of them helping the cell, and the
body as a whole, to work.
Enzymes are involved in all biological reactions, e.g. cellular respiration, photosynthesis and protein
synthesis. Without enzymes these vital reactions would be too slow for life to continue. Some
enzymes work inside cells, while other enzymes (like digestive enzymes) work outside the cell.
Examples of enzymes
Each enzyme can usually only be the catalyst for a single reaction. For example, the enzyme maltase is
the catalyst for changing maltose into glucose. Notice that the name of the enzyme is usually very
similar to the substance it works on: maltase works on maltose. Enzymes have the ending -ase. While
maltase can convert maltose to glucose, it cannot take two glucose molecules and put them together
to form maltose. An enzyme can only do ONE job, in ONE direction.
The action of maltase on this reaction is usually written as:
(2)
Some enzymes help to make new substances in the body and others help to break down unwanted
substances in the body. Enzymes not only speed up reactions, they are also located or released in very
specific places, at specific times. This helps to ensure that all reactions happen in the right place and
at the right time.
In the digestive system, enzymes break down large insoluble molecules (e.g. starch, proteins and fats)
into small soluble molecules that can be absorbed into the blood from the small intestines.
Large
Insoluble
Molecule
Type of
Enzyme
Small Soluble
Product
Carbohydrate
(e.g. Starch)
Amylase
Carbohydrase
Starch-> maltase
Maltose-> glucose
Protein
Protease (e.g.
pepsin)
Proteins 
Amino Acids
Fat/Lipids
Lipase
Lipids  Glycerol
and Fatty Acids
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Properties of enzymes
1. They are all proteins, which is one reason why we need protein in our diet.
2. They are all biological catalysts.They speed up a reaction without being used up; this means
they can be used over and over again.
3. A small amount of enzyme can effect the change of a large amount of chemical.
4. The way enzymes work is affected by temperature, pH and pressure. They can be denatured
(destroyed) by excessive heat.
5. The reactions are reversible.
6. Enzymes are specific that is they control only one reaction. So maltase only acts on maltose,
sucrase on sucrose etc.
How do enzymes work?
Enzymes are thought to have an area with a very particular shape. When a molecule of the right
chemical for that enzyme comes along it will fit exactly into the shape. The area of particular shape is
called the active site of the enzyme, as that is where the reaction takes place. The molecule that the
enzyme works on is called the substrate. After the reaction has taken place and the products of the
reaction leave the active site leaving it ready for another molecule of the chemical.
The active site of an enzyme has such a particular shape that only one kind of molecule will fit it, rather
like a particular key fitting a lock. This is why enzymes are specific in their action.
Effect of Temperature and pH
Increasing the temperature increases the kinetic energy of the enzyme and substrate molecules so that
they move faster and are more likely to collide. So increasing the temperature increases the rate of the
reaction up to a certain temperature. This temperature is known as the enzyme’s optimum
temperature. Different enzymes have different optimum temperatures. The enzymes in animal bodies
work best at 37˚C.
If the temperature is increased beyond the optimum the enzyme has
so much kinetic energy that the bonds holding the enzyme molecule
together start to vibrate and eventually break. The enzyme loses its
specific shape so that the substrate no longer fits in to the active
site. We say that the enzyme is denatured.
Enzymes also have an optimum pH. Different enzymes have
different optimum pHs, e.g. pepsin found in the stomach works best at pH 2, which is why the stomach
produces hydrochloric acid.
Although enzymes in our bodies work best at 37°C, some very special enzymes can even work well at
75°C and they form the basis of a technique used to make lots of DNA from tiny amounts found at
crime scenes. This technique is called the Polymerase Chain Reaction (PCR) and uses an enzyme called
Taq polymerase – an enzyme that works best at 75°C. Taq is a nickname for Thermus aquaticus, a
bacterium that happily survives and reproduces in hot springs - an environment that is lethal to other
organisms. You can find out more about PCR here.
Use of enzymes in the home
Enzymes can be taken out of organisms, purified and then used in science and industry.
One common use in the home is in biological washing powders. These contain amylase, lipases and
proteases and break down any stains that contain carbohydrate, fat and protein. They therefore digest
“biological” stains from the clothes. Since enzymes work at a low temperature this saves electricity and
makes them good for delicate fabrics.
Some people, however, are allergic to the enzymes and suffer skin problems.
Enzymes in food
Many enzymes are used in the preparation of many different foods.
For example, amylases which are present in yeast are used in brewing and baking to convert sugars
into alcohol and carbon dioxide.
Proteases are used in tenderising meat. Rennin is essential to create cheese.
Invertase is used to make some soft centred sweets such as thin chocolate covered mints. A thick,
almost solid, paste of sucrose and a little water containing invertase is covered in chocolate and left at
room temperature for a few days. The sucrose is converted into a mixture of glucose and fructose
which creates a soft centre to the chocolate..
Other uses of enzymes
Enzymes are used in many industrial processes.
Here are some examples of enzymes and their uses.

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Amylases - used in textile and paper production
Ficin - used in photography processes
Pepsin - used in the pharmaceutical industry
Bacterial proteases - used in making leather, textiles and in laundry
Catalase - used in rubber production
Taq polymerase - used in amplifying DNA found at crime scenes
It is possible to attach enzymes to small bead made of alginate. Enzymes that have been fixed in this
way are called immobilized enzymes. Immobilised enzymes are widely used in industry because it
allows the reaction to flow continuously and the product will not be contaminated with the enzyme so
will not need to be purified.
Uses of immobilized enzymes

Immobilized enzymes are used in the production of lactose free milk for people who are lactose
intolerant.

Immobilized sucrase can be used to convert sucrose into
the much sweeter glucose and fructose to sweeten low
calorie foods.

Immobilized enzymes are used also used in glucose
testing strips to measure glucose levels for diabetics.