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How Enzymes Work

Enzymes are proteins that act as biological catalysts, which means their function in the body is to vastly increase the rate of reaction between chemicals that would not otherwise happen: thus making life possible. Enzymes work by reducing the activation energy of a reaction, this means that with an enzyme present, less energy is needed for the reaction to happen and hence it allows that reaction to occur. For an enzyme reaction to happen, the substrate (chemicals that are being reacted together) goes to the active site (the part of the enzyme that does the work). Crucially, it is the enzyme's shape that is important.

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The induced fit hypothesis explains how the enzymes work. The active site of an enzyme is the area where reactions take place. The substrate is the chemical that the enzyme is reacting together. According to this explanation for how enzymes work, the two do not fit perfectly, and so the shape of the active site changes slightly to fit. The reaction takes place and the enzyme returns to its original shape.

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induced fit hypothesis diagram


Factors Affecting Enzyme Activity

  1. 1
    Temperature has an important influence on the rate of activity of an enzyme. To begin with, if you increase temperature, the rate of reaction goes up because the enzyme and substrates are moving about more, and have more energy. However, if you go beyond an optimum point, the activity decreases. This is because the enzyme denatures as hydrogen bonds break, and the enzyme looses its distinctive shape. A similar effect is seen when pH is changed.
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  2. 2
    Substrate Concentration.
    Increasing substrate concentration will increase the reaction rate, but eventually, this rate will level out because the enzymes can only do so much work and the maximum number are being used up.
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  3. 3
    Enzyme activity can be reduced by the presence of inhibitors; there are two types.  
    1. A competitive inhibitor has a similar structure to the substrate - so it can fit into the active site and it stops the enzyme catalyzing the actual substrate. All the time, the rate of reaction is reduced.
    2. A non-competitive inhibitor binds to part of the enzyme. This alters its shape and therefore stops it from working correctly. Many poisons are this type of inhibitor, for example: cyanide.
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  4. 4
    Allosteric Site.
    Another way of affecting the rate is molecules binding to the allosteric site on an enzyme. This is another part (not the active site) that tells the enzyme to work or not. The presence of these molecules will inhibit or activate the enzyme. However only a few very special enzymes do this.
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Digestive Enzymes

Because of their importance, we will look at the different digestive enzymes in the table below.

Substance Enzymes What Happens Carbohydrates
Amylase Disaccharidases The salivary amylase begins digestion in the mouth, but not much happens since food only stays there for a short while, but it keeps the mouth clean Amylase from the pancreas breaks down starch into maltose. When the maltose gets into the [[biology/humans/digestion.htm]l ileum], the last stage of digestion takes place and the disaccharides are broken into glucose so they can be absorbed by the process of [biology/cell/transport.html active transport]].
Proteins Endopeptidases These are produced in the pancreas and also as pepsin in gastric juice. This enzyme slices up polypeptides into smaller ones of about 6-12 monomers. It does this at different points depending on the enzyme. This also leaves a lot of ends to help the next enzyme.
Proteins Exopeptidases These proteins live in the ileum membrane, they finish off the job and break the proteins into individual amino acids; which can now be absorbed into the blood stream. Triglycerides Lipase


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Categories : Biochemistry

Recent edits by: Taylor (ScienceAid Editor), Jamie (ScienceAid Editor)

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