Investigating the properties of enzymes.

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Background

Enzymes are proteins. They are biological catalysts that speed up reactions. An example of enzyme action is digestion, where large food molecules are broken down into simple small molecule that can be absorbed across the gut wall into the blood.

Enzymes are said to be specific, that is that the enzyme will only work on one food or substrate to produce the products.

        All living organisms during their metabolism produce Hydrogen Peroxide as a waste substance in many cells. (The enzyme is found in every living cell). This Hydrogen Peroxide is toxic and very dangerous and so must immediately be broken down into harmless products. For this reason every cell has the enzyme catalase which breaks up the Hydrogen Peroxide into water and oxygen.

Catalase + H2O2                 H20 + 02     

The reason why enzymes can only break down one substrate is because of their active sites. Enzymes are 3 –D proteins which have on their surface a code. The substrate has the same code on its surface and the two lock together. The enzyme tweeks the substrate molecule and the two products are separated and released. The enzyme is freed to be used again.

Properties of enzymes

  1. Enzymes are biological catalysts which speed up reactions
  2. They are 3 – D proteins with active site
  3. Enzymes are said to be specific – each enzyme only has one substrate which it locks into. For example catalase will only work on Hydrogen Peroxide.
  4. Optimum temperature – this is the best temperature - Enzymes work at its faster rate. However, high temperatures will denature the enzyme. This means that the active site is destroyed or altered so that it will not lock onto its substrate any longer.
  5. Optimum pH – most enzymes work at their fastest around pH 7. This is because acids and alkalis that are too strong can damage their active sites and so the rate of reaction falls. However some enzymes e.g. those in our gut tolerate a particular pH.
  6. Enzymes can be used again and again because they are unchanged after a reaction.
  7. The more substrate there is the more reaction will occur.
  8. The more enzyme there is the faster the rate of reaction.

Enzymes can also be used in our daily life. Biological washing powders contain enzymes. These will digest food stains and include proteases and lipases which digest grease stains.

Fruit juices also contain enzymes. Pectinase is used to break down the enzyme. Immobilised enzymes are attached to tiny beads and these prevent the enzyme from being filtered and lost and so the enzyme can be saved and used again and again.

   

Planning

Aim: An experiment to show how an increase in the amount of enzyme affects the rate of enzyme action.  

Apparatus:

  • Potato chip which has on its surface enzymes
  • Hydrogen Peroxide which is a catalyst and turns to water rand oxygen
  • Water so we can count the bubbles
  • Measuring cylinder to measure the amount of hydrogen peroxide needed
  • Tile and knife to cut the chip onto into a number of pieces
  • Test tube for the water to be placed in
  • Syringe so we can collect the hydrogen peroxide into
  • A side arm test tube to place the hydrogen peroxide and chip into.
  • A test tube rack to hold the side arm test tube and a smaller test tube which is filled with water
  • Wet paper towel in which 6 potato chips will be kept to keep them moisturised
  • pH paper for pH of the solution
  • Thermometer to measure temperature of solution
  • Stopwatch to count bubbles for 5 minutes
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Prediction  

I predict that increasing the surface area will increase the amount of exposed catalase. I would expect the number of oxygen bubbles per minute to increase which indicates an increase in the rate of enzyme action. WHY? Because there is more surface area, there would be more catalase therefore more active site combining with Hydrogen Peroxide at any one time and more oxygen bubbles being produced.

Constants

Throughout the experiment we are going to keep the pH, ...

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