B2 - Enzymes

  • Created by: Noxas
  • Created on: 12-04-19 20:01

What are Enzymes?

Enzymes are often called biological catalysts - this is because they speed up internal reactions in the body.

Each enzyme has a specific active site, which has a shape that will only fit to a specific substrate to break it down. This is often explained by the lock and key theory.

Active Site:

  • binds to the reacting chemicals
  • only fits one substrate
  • has an important, specific shape
  • catalyses a reaction

Lock and Key Theory:

  • The active site is the 'lock'
  • And the substrate is the 'key'
  • There is only one lock for each key, so one enzyme for each substrate
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Rate of Reaction

The rate at which enzymes work can be effected by different factors.

Although increasing the temperature increases the effectiveness of the enzyme for a short while, once the optimum temperature is reached, the reactivity decreases. This is as a result of the active site changing shape, and the enzyme denaturing.

Enzymes also have an optimum pH, and if the pH is too low or high, the enzyme will beome denatured.

To calculate the rate of reaction, you must divide the change in mass by the change in time. This can be done with numbers, or by drawing a tangent on a graph and finding it's gradient.

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Digestive Enzymes

Digestive enzymes speed up - catalyse - the break down of large, insoluble food molecules into smaller, soluble molecules.

These molecules are used to construct new:

  • lipids
  • proteins
  • carbohydrates

Enzymes in the intestine work best in alkaline conditions - so bile, produced in the liver and stored in the gall bladder, is used to neutralise the HCl (stomach acid) to stop the enzymes denaturing. Bile also breaks up fat droplets into even smaller ones, through a process called emulsification. These droplets have a higher surface area, which increases the rate at which they are broken down by lipase.

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Enzyme Examples


Amylase breaks down starch into sugars, mostly Maltose.

It is produced in the small intestine, pancreas, and salivary glands, and is active in the mouth and the small intestine.


Proteases break down proteins into amino acids.

It is produced in the small intestine, pancreas, and the stomach, and is active in the stomach and the small intestine.


Lipase breaks down lipids into fatty acids and glycerol.

It is produced and active in the small intestine.

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Food Tests


  • Add iodine solution to sample
  • if starch is present, it will turn blue-black


  • Add Biuret solution to sample
  • if proteins is present, it will turn purple


  • Add Benedict's Reagent and heat for two minutes
  • Depending on the concentration, the solution should turn green, yellow, or red


  • To test for lipids, add Sudan III to the solution
  • If lipids are present, a layer of red oil will float on the surface
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