Enzymes
Thousands of chemical reactions take place inside a living thing every second. It is enzymes that make them happen quickly. Enzymes are special proteins made by living things themselves, and they increase the speed of biochemical reactions.
A substance that speeds up a reaction and is left unchanged at the end of it is called a catalyst. Enzymes work in the same way, and because they are organic compounds they are called organic catalysts.
The power of an enzyme — an example
In the laboratory
To break down sucrose and get glucose in the laboratory, it has to be heated with a dilute acid.
Inside your body
The enzymes in the digestive system carry out the same reaction easily, with no acid and no heating, at the body's normal temperature.
Without enzymes, the reactions that must take place in the body would be so slow that they would not finish even within an organism's whole lifetime.
Activity — amylase acting on starch
Let us plan a simple experiment that lets you see an enzyme at work right before your eyes.
Method
- Put 2 ml of a solution made by mixing bread flour with water into a test tube.
- Add the same amount (2 ml) of amylase enzyme solution to it.
- After two minutes, take one drop of the mixture onto a white tile.
- Put a drop of iodine solution on it.
- Repeat this every two minutes until about 20 minutes have passed.
Observation
The first drops show a dark blue colour, but in the samples taken later the dark blue colour of the iodine fades over time. After about 20 minutes, adding iodine shows no colour other than the iodine's own.
Conclusion
We know that iodine turns blue only when starch is present. If that blue colour has disappeared, it shows that no starch is left in the tube. The reason is that the amylase enzyme has broken the starch down into maltose.