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The effects of temperature on catalase in yeast and liver.

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Introduction & Theory: As stated in the headline, this will be a plan to investigate the effects of temperature on the enzyme catalase in yeast and liver. But before I go in to detail about the experiment itself, the biology behind the reaction should be discussed. Starting with what will in great part control the reaction, some knowlegde of the biology of enzymes should be obtained. As we have learned, enzymes may be described as globular proteins with catalytic properties. They cannot cause reactions to occur, but only speed up ones which would otherwise take place more slowly. While the enzyme molecule is normally larger than the substrate molecule it acts upon, only a small part of the enzyme, called the active site, actually comes into contact with the substrate. It is commonly accepted that the enzymes operate on a socalled lock and key mechanism. The lock and key mechanism works in the way that in same way as a lock fits a key, the substrate fits exactly into the active site of the enzyme molecule. There, the substrate is either split into two or more molecules, or two or more molecules may be joined together, as with dipeptide. During the entire process, the enzyme remains unchanged and maintains its initial shape. This allows it to keep turning sustrate into products, being used over and over again. The rate at which enzymes normally work can be shown on a graph as a rapid increase at first, as there is plenty of substrate for the enzymes to bump into and turn into product. At a point though, the reaction will reach its peak. A maximum number of substrate is being turned into product per second/minute. ...read more.


The yeast and liver will be homogenised and used as a yeast/water and liver/water suspension. One reason for doing this is to secure an even enzyme concentration. If we were to use single cut pieces, a piece cut from the center of the yeast/liver may have higher enzyme concentration than one in the outer edges. The best way of keeping this a fair test is in other words to make a suspension, using for instance 1g liver and 50cm3 water. Mixing the sample of yeast/liver will make possibly different enzyme concentrations blend in together. Also, dried yeast ages more quickly, becoming denatured and deteriated. Another important factor is to use the same yeast or liver throughout the entire experiment. If we were for instance to suddenly use a new, fresh piece of yeast, this could contain a higher concentration of enzymes than the original. Seeing as a higher concentration of enzymes would produce more substrate at a quicker rate, this would make the experiment inaccurate. Another necessity in order to make this a fair test is in other words to use the same sample of yeast/liver throughout the experiment. As for the substrate, we need to use the same concentration and volume for all samples. The way in which we can make sure of this is to make out one mixture of H2O2, for instance 50 cm3, and use fractions of this for all the samples. The opposite, making new concentrations for each sample would make this variable anything but constant. Changing the concentration would affect the results, as a higher or lower concentration would produce different amount of products at different speeds. Important for both is to keep a constant volume. ...read more.


Hydrogen peroxide is not flammable. 10 C 20 C 30 C 40 C 50 C 60 C Yeast Liver Yeast Liver Yeast Liver Yeast Liver Yeast Liver Yeast Liver Initial volume (cm3) Table: Table of initial volume of water in burette: Table of temperature vs rate of oxygen gas release 10 C 20 C 30 C 40 C 50 C 60 C min sec Volume (cm3) No of bubbles Volume (cm3) No of bubbles Volume (cm3) No of bubbles Volume (cm3) No of bubbles Volume (cm3) No of bubbles Volume (cm3) No of bubbles 30 1 1 30 2 2 30 3 3 30 4 4 30 5 5 30 6 6 30 7 7 30 8 8 30 9 9 30 10 Area where error could occur: * Volume of gas emitted exceeding that of the burette's volume, oxygen gas escaping into free air. This would make further readings impossible, and the final volume could not be recorded. * The bung might not be fitted tightly enough into the boiling tube and oxygen gas might leak out through the space between the bung and the sides of the boiling tube. All results obtained would be inaccurate. * Oxygen gas might also be lost if it the pipette misses the opening of the burette. In that case, the gas would rise to the surface of the water outside the burette. Inaccurate readings would be the result. Method to avoid this: * Be wary not to use too large amounts of hydrogen peroxide, 5 cm3 should be enough to observe a reaction. Also be careful to fill the burette with as much water as possible. * Fit bung tightly into the boiling tube, taking care that no oxygen gas escapes. * The pipette must be kept directly under the opening of the burette, preventing the potential loss of the oxygen as the reaction is taking place. ...read more.

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