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Unit 2 - Enzymes

Enzymes are proteins and their molecules act as biological catalysts. This means that they speed up chemical reactions in living organisms, and in this GCSE Biology quiz we are going to take a closer look at some of the different enzymes, what they do and how they work.

Enzymes function because they are long molecules that are twisted and folded into a specific and usually very complex shape. The shape allows smaller chemicals (substrate molecules) to fit into certain places called active sites. This brings the substrate chemicals close together and so they can react more easily than they would do otherwise.

Enzymes work best at specific temperatures and pH levels, for example, human enzymes work best at about 37oC. They are sensitive to temperature and pH, and change their shape under conditions of moderately high temperatures (45oC and above) and values of pH that differ from the ones in which they normally work. When they change shape like this, we say that they are denatured and the active sites will no longer work as efficiently. As the temperature or pH becomes more extreme, the active sites stop working altogether.

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Enzymes are found at work in almost all places in the body of any organism, whether plant, animal or bacteria. They are catalysts for many biological processes such as respiration, photosynthesis and the synthesis of proteins. They also break down longer molecules into shorter more useful chemicals e.g. during digestion, enzymes convert large molecules into smaller molecules which can then be absorbed. Because they can be used to cut other molecules, they are used in genetic engineering. They are carefully chosen to cut specific genes from the DNA of plants and animals which can then be spliced into other DNA. They are even used in industry to catalyse reactions at normal pressure and temperature thus saving money on expensive energy-demanding equipment that would otherwise be needed.

Try this quiz and test your knowledge of enzymes - the proteins and biological catalysts.

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  1. Enzymes are which type of molecule?
    They are very complex molecules
  2. Which of the following emulsifies fats so they can be further digested by the enzyme lipase?
    Bile is made in the liver and stored in the gallbladder. It is released into the digestive system through the bile duct
  3. Which enzyme converts fats into 3 fatty acids and glycerol?
    When you see a bioligical word that starts with 'lip' or 'lipo' it will usually indicate something to do with fats
  4. Isomerase enzyme is used in industry for making high fructose syrup from which of the following?
    High fructose syrup is used to sweeten diet foods because it is much sweeter than other sugars, so less of it is required. This means fewer calories for the same sweetness
  5. Which enzyme converts starch into sugars in the mouth and small intestine?
    Enzyme names usually end with 'ase'
  6. Protease enzymes break down proteins into what?
    These can then be re-assembled by other enzymes into new, different protein molecules exactly where they are needed
  7. Which enzyme is used in industry to convert starch to glucose?
    Other examples include the use of the enzyme rennin to make cheeses and esterases that break down certain chemical bonds in glues and adhesives during the recycling of paper
  8. Which word describes the change of shape when an enzyme is heated to high temperatures?
    Some students believe that enzymes are 'killed' by heat and extremes of pH. They are not - enzymes can't be killed as they were never alive! Denatured is the correct word to use in exams
  9. Protease enzymes are located in which organ?
    Protease enzymes are also located in the small intestine. The stomach protease works best at pH 2 and the one in the small intestine works best at pH 8
  10. The shape of an enzyme will change if which of the following is increased?
    The temperature at which the enzyme works best is called the optimum temperature. For most human enzymes, this is body temperature, 37 degrees C. As the temperature increases above the optimum, the enzyme changes shape due to bonds breaking which hold the shape. The enzyme can no longer work so enzyme activity is reduced

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