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A photographic company wants to recycle the plastic in exposed (and therefore unusable) photographic film. They will need to remove the silver compound attached to the film by the protein gelatine. They decide to use a protease enzyme called trypsin

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Introduction A photographic company wants to recycle the plastic in exposed (and therefore unusable) photographic film. They will need to remove the silver compound attached to the film by the protein gelatine. They decide to use a protease enzyme called trypsin to digest the gelatine, but want to find the best conditions for the enzyme to work to save money. Background knowledge ENZYMES An enzyme is a biological catalyst that speeds up the rate of reaction. Enzymes are composed of polymers of amino acids. Enzymes are mainly located in the cytoplasm of a cell. Here they control the chemical reactions occurring inside the cells. The enzymes break down the food molecules into smaller parts so it is much easier for it to pass through the blood stream. Many enzymes are produced in different parts of the digestive system. The digestive system produces enzymes that break down the components of the food we eat. They speed up reactions by a process called the induced fit theory. It was first thought that the 'lock and key' hypothesis was how the enzymes work, but this is now believed to be incorrect because the enzymes can change shape so that the substrate (the thing that is broken up) can fit into the active site of the enzyme, which is why it is called the induced fit theory. The lock and key theory suggests that the enzymes are the correct shape without having to change for the substrate to fit in, which they often are not. The substrate enters the enzyme and is digested in the active site of the enzyme. WHAT IS TRYPSIN? Trypsin is an enzyme that acts to degrade protein; it is often referred to as a proteolytic enzyme, or proteinase. Trypsin is one of the three principal digestive proteinases, the other two being pepsin and chymotrypsin. In the digestive process, trypsin acts with the other proteinases to break down dietary protein molecules to their component peptides and amino acids. ...read more.


However at around 60 oC, the denaturisation process will affect the enzyme more than the kinetic theory, meaning there will be a bigger decrease in the rate of reaction, or, the rate of reaction will stop. A predicted graph of the rate of reaction of trypsin as temperature increases. The graph show my prediction of what will happen to the rate of reaction of trypsin as the temperature increases. My prediction is supported by the facts that as temperature increases the number of collisions are more numerous and the activation energy can be overcome enabling the particles to react. However trypsin has an optimum temperature at where it will work best and speed up the rate of reaction. After about 50 oC the enzyme will start to denature and therefore slow down the rate of reaction. If the enzyme starts to denature then it will become useless and not be able to digest the protein gelatine as efficiently because the active site would have changed its shape and the substrate would no longer fit into it and react. The rate of reaction will have stopped by about 60oC as a result of this. Apparatus The following equipment will be required: - * A kettle * A beaker * Ice cubes * Exposed photographic film * Trypsin 1% * A splint * A thermometer * A test tube * A stop watch * A measuring cylinder * Scissors * Ruler Method 1) Collect all equipment and set up as shown in the Apparatus. 2) Boil water in the kettle. 3) Pour 200mls of the boiled water in a beaker. This will be used constantly in the experiment so keep it aside for future use.* 4) Cut the photographic film 1cm x 1cm using a ruler and a pair of scissors. 5) Split a splint and place the photographic film in between the split. 6) Measure 4mls of trypsin, being aware of the meniscus (measurement read at eye level), using a syringe. ...read more.


The size of the film was not all ways the same, so if you put two films in two different test tubes in water baths at the same temperature, then you might get one film transparent before the other even though everything else is the same. This is because the surface area of the film that is slower at turning transparent compared to the other film that was transparent before is greater and this doesn't make my results 100% reliable. A reason for my anomalous result could be that as the Trypsin was produced on 24/9/02 and was used on 3/10/02 when we opened the flask which contained trypsin, we left the lid open so it is left to be contaminated by the infectious environment (Bacteria or germs). So this might be the reason why the reaction was slower than expected at 30?C. Learning from this the overall improvements I could have were... * to keep the lid on the flask containing trypsin, use a light on one side of the test tube and a light sensor on the other side of the tube connected to a stopclock so when the light sensor detects light through the acetate when it is clear, it would stop the clock (this would eliminate the problem of human error in stopping the clock at an incorrect time) * measure all the film pieces at exactly the right size for a fairer and more accurate result * make sure the trypsin was fresh and cold * try different types of photographic film * conduct the experiment at more temperatures for example 35 degrees 45 degrees etc. * use an electronic temperature probe Extension I could do an extension by controlling a different factor while doing this experiment like the size of the film or the concentration of the trypsin. The experiment could be repeated but instead of measuring the time against temperature it could be measured against the concentration. The film would be dropped into different concentrations of trypsin in a controlled environment and the time measured for the film to become clear measured. ...read more.

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