Biology - Enzymes

Enzymes are biological catalysts and are made of protein. They catalyse the reactions in the body. One advantage to using enzymes rather than just increasing the temperature of the body is that enzymes will only catalyse the reactions that you want them to.

This is because each type of enzyme has a different shape. This means that only one type of substance can fit into its active site. (The substance that is broken down is known as the substrate.) They work by randomly bumping into the substrate and breaking it down, then bumping into another one.

For enzymes to work, they need the correct temperature and pH. If the temperature is too low, there isn't enough energy for the particles to "bump" into the enzymes. If the temperature is too high, the enzyme will lose its specific shape, becoming denatured.

When you eat food, it first enters the mouth. You break it down physically (chewing) and chemically (enzymes).

The enzyme released in the saliva is amylase. It breaks down carbohydrates into simple sugars.

Amylase needs a pH of about 7, which is why saliva is neutral (try touching a piece of indicator paper to your tongue). The warmth of the mouth also provides a perfect temperature for the enzymes.

After chewing, you swallow the food.

In the stomach, food is broken down physically (the walls of the stomach pummel the food) and chemically (with enzymes).

The enzyme released in the stomach is protease. It breaks down proteins into amino acids.

Protease requires acidic conditions. The walls of the stomach secrete hydrochloric acid to provide this condition.

After digestion in the stomach, the sphincter muscle allows the food through to the small intestine.

In the small intestine, food is only broken down chemically (with enzymes).

Amylase breaks down carbohydrates into sugars

Protease breaks down protein into amino acids

Lipase breaks down fats into fatty acids and glycerol.

Bile (produced in the liver and stored in the gall bladder) is also released here. It is alkaline, and its job is to neutralise the acidic stomach acid and emulsify fats, so that the lipase has a larger surface area on which to work (it does not break them down, it just emulsifies them).

In the small intestine, the broken down food is absorbed into the bloodstream.

In the large intestine, excess water is absorbed into the bloodstream. Any nutrients that were not absorbed in the small intestine can also be absorbed here.

The large intestine is lined with villi, which are tiny hairs that increase the surface area of the small intestine massively. This means that there is a greater surface area through which substances can be absorbed.

No enzymes are secreted here, you will be pleased to know.