GCSE Biology: Lock & Key Theory

5th April 2017

GCSE Biology Revision

Lock and Key theory for the GCSE Biology syllabus


The lock and key theory is all to do with enzymes and what they do. Enzymes are extremely important as they allow chemical reactions to take place, and without that, processes such as digestion just wouldn’t happen.


Enzymes speed up chemical reactions in our cells and work best when they are in optimum conditions - if it gets too hot, enzymes become denatured and do not function as efficiently. Importantly however, enzymes do not ‘die’ because they are not living things. For more information about the role that enzymes play in the process of digestion, have a listen to our song ‘Enzymes and Digestion’ which can be found here.


The active site of an enzyme is the most important part because it is the place where molecules bind to the enzyme and the chemical reaction occurs. pH level and temperature affect the size of the active site. The larger the active site, the more efficient the reaction.


The lock and key theory is linked to the fact that enzymes are designed to have one very specific job and thus, can only speed up one specific reaction. This is why we have lots of different enzymes because each one can only do one job. Protease enzymes for example can only break down protein molecules. It is called the lock and key theory because there is only one good fit for each lock - it is the same for enzymes.

For more information about the topics that are likely to come up in your GCSE Biology exam, take at all the available songs for GCSE Biology, GCSE Chemistry and GCSE Physics.


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