Enzymes are biological catalysts: this means that they speed up the chemical reactions in living things. Without enzymes, our guts would take weeks and weeks to digest our food, our muscles, nerves and bones would not work properly and so on – we would not be living!

A catalyst is any substance which makes a chemical reaction go faster, without itself being changed. A catalyst can be used over and over again in a chemical reaction: it does not get used up. Enzymes are very much the same except that they are easily denatured (destroyed: but do NOT use this word since the protein molecule is not broken down into amino-acids, it just loses it shape and will not work any more) by heat. Our enzymes work best at body temperature. Our enzymes also have to have the correct pH.

All enzymes are made of protein; that is why they are sensitive to heat, pH and heavy metal ions. Unlike ordinary catalysts, they are specific to one chemical reaction. An ordinary catalyst may be used for several different chemical reactions, but an enzyme only works for one specific reaction.

Human saliva contains an enzyme called amylase. This enzyme helps to turn starch into a sugar called maltose. When you swallow a mouthful of food, the amylase stops working because it is much too acid in the stomach pH 2. Amyalse works best in neutral or slightly alkaline conditions, i.e. at about pH 7. When your food gets into the small intestine, more amylase is made by the pancreas and this turns the remaining starch into maltose. Another enzyme (maltase) turns all this maltose into glucose. Glucose is then absorbed into the blood.

Enzymes in the human alimentary canal and what they digest:

Enzyme  ~  Substrate

  1. Amylase  ~  Starch
  2. Maltase  ~  Maltose
  3. Sucrase  ~  Sucrose
  4. Lipase  ~  Fats
  5. Pepsin  ~  Proteins

All animals, green plants, fungi and bacteria produce enzymes: so enzymes are not just about digesting food. The enzymes which we use to digest our food are extra-cellular, that means they are found outside cells. We also have enzymes inside our cells; these are intra-cellular enzymes. Enzymes are used in ALL chemical reactions in living things; this includes respiration, photosynthesis, movement growth, getting rid of toxic chemicals in the liver and so on.

Viruses are rather different, but you do not need to know much about them for GCSE, so just make sure that you don’t catch any!

Enzymes must have the correct shape to do their job. They are made of proteins, and proteins are very easily affected by heat, pH and heavy metal ions. Some people say that enzymes work like a key in a lock. If the key has been twisted by heat, or dissolved in acid or stuck up with chewing gum it will not work. Enzymes change their shape if the temperature or pH changes, so they have to have the right conditions. Copper ions are poisonous: if you get copper ions in your blood they will block up some of the important enzymes in red and white blood cells.

21 Responses to Enzymes

  1. Carlos Benites says:

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  4. Steven Olson says:

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  5. Dominic Danh says:

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  6. alex says:

    i have a quesion what actully makes an enzyme and how can you make one your self and what is its molucule compact

    • As it says on this page, enzymes are made of protein. Your body makes many different enzymes, eg. the amylase in your saliva. When cells make enzymes, they use the information in a piece of DNA to join amino-acids together in the correct order: the sequence of amino-acids in a protein determine the 3 dimensional shape of the protein. All enzymes need the correct 3D shape to do their jobs. If the shape of the protein is wrong, it will not work as an enzyme.

      Sorry, but I don’t know what you mean by molecule compact.

  7. Leo... says:

    Super werbsite. So much better than my revision book
    I am so glad that i am not the only German doing IGCSEs
    Danke Dominic Danh!!!

  8. Katerina Chatnernobic says:

    besides the enzyme pepsin, what suffix do you notice is associated with all of the en page??

  9. Blagovest Alexandrov says:

    Hello !
    Can I get a detailed materials enzymes as: precursors of enzymes, sinthesis, mechanism of action and your inhibition.
    I need this information for a research project from university.
    I will your be very grateful for the support.

    • If you are a University student, you should be able to ask a question that makes sense. You should also be able to spell “synthesis”. I have no idea what you mean by “my” inhibition.

      Enzymes are proteins. RNA is used to determine the sequence of amino-acids used when a protein is synthesised. An enzyme precursor is a a protein that does not work as an enzyme because it has an extra bit of amino-acid sequence on the protein. When this extra bit is removed, it will function correctly as an enzyme.

      Enzymes can be inhibited (stopped from working) by inhibitors, these changes the shape of the protein molecule.

      • set mateus says:

        may you plese tell me the relationship between enzymes and ph and between enzymes and temparature.

        • At the optimum (best) pH an enzyme works at its fastest rate. If the pH is higher or lower the enzyme works more slowly and if the pH is much too low or much too high the enzyme just stops working at all.

          Increasing the temperature makes an enzyme work faster and reducing the temperature makes it work more slowly. However, above 45 degrees C it will slow down and even higher it will denature the enzyme, ie destroy it, but there are some bacteria that can live at very high temperatures so their enzymes work in scalding hot water. Of course, at freezing point, enzymes will stop working.

  10. redday21 says:

    What does “optimum temperature” mean in relation to an enzyme?

    • Nigel Purchon says:

      This is just the best temperature for the enzyme to work. The reaction will be slower if the temperature is lower or higher than the optimum.

  11. redday21 says:

    Do the reactions happen quicker or slower with an enzyme? Why?

  12. redday21 says:

    Can an enzyme and substrate react more than once?

    • Nigel Purchon says:

      Enzyme molecules are unchanged by the reaction: they are used again and again as long as there is still some substrate remaining.

      Substrate molecules are turned into a product, this happens once for each substrate molecule; once a substrate molecule has reacted that is that.

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