Biological Catalysts…

A catalyst is a substance that enables (or speeds up) a chemical reaction without itself being altered by that reaction. Catalysts, therefore, are not used up as they influence a reaction. Enzymes are biological catalysts – in other words catalysts that operate within living things. The names of enzymes are usually made by putting -ase on the end of the thing the enzymes are acting upon. There are two groups of enzymes:

• Intracellular – metabolic enzymes that act inside cells to control all the normal reactions that keep you alive.
• Extracellular – acting outside the cells such as digestive enzymes.

Enzymes are proteins that have a very particular shape that allows them to change the way chemicals around them behave. They may contain mineral elements like magnesium or iron to help them to do this. They are very much affected by temperature. At the ideal body temperature of the organism in which they are found, they will run at near maximum efficiency. At lower temperatures they will work more slowly. As the temperature increases above the ideal, they may change shape slightly which causes them to slow down. At a sufficiently high temperature they may be permanently damaged. When proteins, including enzymes, suffer a permanent shape change we say they have been denatured. The classic example is the protein in an egg. When it turns from clear to white it has been denatured and there is no way to get it to go back to how it was before.

Digestive enzymes break insoluble food molecules down into soluble ones. The enzyme in saliva that breaks starch down into soluble sugar (maltose) is called salivary amylase. The first ever enzyme to be identified and purified was pepsin. It is produced by cells within the stomach and it is a protease. Proteases break proteins down into smaller molecules. Several digestive proteases combine within the digestive system to break protein down into individual amino acids.

Lipase is the enzyme that breaks fat down into smaller fatty acid molecules & glycerol that can be more easily absorbed into the blood stream. Some micro-organisms can produce cellulase capable of breaking cellulose down into glucose. Cellulose is the molecule that makes up plant cell walls and provides indigestible fibre to our diet. Animals that eat grass, such as cattle, play host to large populations of cellulase producing organisms so that they can extract some nutrition from their hard-to-digest food.

Another important enzyme is catalase. It is present in most aerobic organisms and plays an important role protecting organisms from the damaging effects of oxygen compounds that form within the body. Hydrogen peroxide (H₂O₂), for example, is broken down by catalase to release oxygen gas and water. The slow release of energy from glucose is done in stages with enzymes controlling every step.

I mention enzymes quite often on this blog (typing enzyme into the search box produces these results) and the idea of biological catalysts is an important one to understand. Many reactions are just too slow (or don’t happen at all) without the encouragement they get from the correct enzyme.

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Questions…

1. What is the name of the process that releases energy within cells?
2. How could you show that the gas given off when hydrogen peroxide decomposes is oxygen?
3. What are the seven main components of a balanced diet?
4. What is the universal energy molecule that is produced during the process described in Q1?
5. Suggest a situation involving a non-biological catalyst.