Enzymes Ava campbell

What are enzymEs?

Enzymes are biological catalysts. They are proteins that speed up chemical reactions in our cells without being used up themselves. The reactions they speed up include respigration, photosynthesis, DNA replication, protein synthesis and digestion.

Every type of enzyme is specific, they will only do one job. This is because the shape of the enzyme molecule will have to match the shape of the substrate molecule (the molecule it reacts with). The parts that match are called the active site. This is also called the lock and key model as just like only one key can open one lock, only one type of enzyme can speed up a specific reaction.

The active site is the most important part of an enzyme as it is where the molecules bind and the reaction occurs. Anything that changes the shape of the active site stops the enzyme from working. This is also like a key. It doesn't matter what the key handle looks like, if you change the shape of the teeth the key will no longer work for that lock. It doesn't matter what type of enzyme it is, if the shape of the action site is changed it will no longer work for that reaction.

What affects the shape of the active site?

Both the temperature and the ph can affect the shape of the active site. Enzymes will only work with a specific ph and temperature.


When the temperatures are low the enzymes reactions are slow. They speed up as the temperature increases until an optimum temperature is reached. This temperature is about 37 degrees Celsius. After this point the reaction will slow down and eventually stop. The rate of reaction increases as the temperature increases because there is more heat energy which causes more collisions with more energy between the two molecules. If the temperature gets too high the enzyme will stop working as it will be denatured.


Every type of enzyme will work best in a different ph. The majority of enzymes work the best in neutral conditions. If the ph is changed the reaction will slow down and eventually stop. Some enzymes are adapted to work faster in unusual ph conditions.

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