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The specially shaped site on an enzyme where the substrates of the reaction bind. It is formed by the folding of the amino acid chains which make up the protein.

Amino acid

The basic building blocks of proteins. There are twenty amino acids used, in different combinations, to make every protein required by the human body.


The process by which the folding of the long chains of amino acids making up a protein is damaged and destroyed by heat, pH changes etc, changing the structure and function of the entire molecule.


A polymer made up of amino acids joined by peptide bonds. The amino acids present and the order in which they occur vary from one protein to another.

Why temperature control matters

The outside of your body - your skin - may feel very hot on a sunny summer's day or very cold when it is frosty and snowy. But it is very important that your internal core temperature stays around 37°C whatever the weather and whatever you are doing.

What affects your body temperature?

There are three main factors which can affect your core body temperature, sending it up or down.

  • The energy produced by your muscles during exercise can make your core temperature go up
  • Fevers caused by disease can make your core temperature go up
  • The external temperature rising or falling can make your core temperature go up or down

Why is core temperature so important?

Enzymes are protein molecules which act as biological catalysts, speeding up and controlling all the reactions taking place in the cells of your body. 37°C is the temperature at which these enzymes work best. A few degrees cooler and they work so slowly that the reactions in your cells do not go fast enough to keep you alive. A few degrees higher and the enzymes denature, so they cannot work at all and you will die.

Read more - hyper and hypothermia

Temperature graph

The effect of temperature on enzyme action

How do enzymes work?

An enzyme is a protein molecule. Each type of enzyme catalyses a particular reaction or type of reaction. They can do this because the long chains of amino acids which make up the enzyme are folded into a particular shape known as the active site. This allows other molecules - the substrates of the reaction - to fit into the enzyme. This works like a lock and key. Once the substrate is in place in the active site it binds to the enzyme and the reaction then takes place rapidly. The products of the reaction are released from the surface of the enzyme.

Why do enzymes stop working if the temperature goes up?

Enzymes are proteins. If the temperature goes up above about 40°C the long amino acid chains begin to unravel. This changes the shape of the active site. The substrate no longer fits and binds to the active site so the enzyme can no longer catalyse the reaction.

Question 3

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Explain how enzymes work.

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