Maintaining Balance

Maintaining Balance


Most organisms are active in a limited temperature range

Identify the role of enzymes in metabolism

Enzymes are protein molecules. They are catalysts that increase the rate of chemical reactions that occur in living organisms. Without enzymes metabolism would be so slow that insufficient energy would be available to maintain life.

Describe the chemical composition of enzymes and use a simple model to describe their specificity of substrates

The substances being acted on by an enzyme is called a substrate. The substance/s obtained as a result of the enzyme action are called the products.


Names of enzymes usually end in ‘ase’. An example is lipase which acts on lipids. An exception is pepsin.

Enzymes are highly specific in their action. This is because the shape of the active site of the enzyme matches only one type of substrate. Proteins are all a chain of amino acids, but they fold into a 3D structure, giving each different protein a unique shape.

▪ A simple lock and key model

At a molecular level, the shape of an enzyme permits it to bind at a particular site (active site) to the substrate molecule (or molecules), causing a reaction to occur. This can be thought of as a key (the substrate) fitting the lock (the enzyme). Unless the key is right for a particular lock, it won’t open the door.

It is thought that the enzyme only fits particular molecules to cause them to react. The enzyme is not used up in the reaction and can be used again. This model of enzyme function is sometimes the lock and key model. It works a bit like this:

Substrate + enzyme(enzyme/substrate complex(products + enzyme

The complex between the enzyme and the substrate (or substrates) molecules reduced the energy required to get the reaction to happen (activation energy).

▪ An induced fit model

A more refined explanation or model for enzyme function is that the shape of the enzyme on its own does not...

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