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An investigation to measure the rate of reaction of hydrogen peroxide decomposition by catalase in yeast

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Introduction

An investigation to measure the rate of reaction of hydrogen peroxide decomposition by catalase in yeast For this investigation I have been asked to investigate (by experimentation) the effect of substrate concentrations on the rate of the decomposition of hydrogen peroxide when catalysed by the enzyme catalase. This is part of our work on the function of enzymes, how they work and the effects of conditions on how they work. This experiment will look at various concentrations of substrate and enzyme, and will also look at how this will affect the rate of decomposition, using graphs and tables. In organisms, hydrogen peroxide is a toxic waste product of metabolism. Hydrogen peroxide on its own is relatively stable and each molecule can stay in this state for a good few years. Its decomposition therefore needs to be speeded up greatly in order to prevent it from intoxicating the cell. This is where catalase is used. Catalase has to be very fast acting to keep the hydrogen peroxide levels low, and it is one of the fastest acting enzymes known. It catalyses the decomposition of hydrogen peroxide, losing oxygen gas as effervescence. Due to an enzyme's functional shape its substrate binds only at a unique location on the enzyme's surface, called the active site, where the chemical reaction occurs. ...read more.

Middle

I will wash the vessels in between reactions, and ensure that the substrate yeast stay at the same temperature by keeping them away from influential heat sources. Concentration of substrate (2H2O2) This is the changeable variable of the experiment. This will affect the reaction the most of all of the factors. I will control it through using water to dilute it to the extent that I need, starting from 20% concentration. This will then be decreased to 16%, 12%, 8%, and 4%. I found that during the preliminary work that this will ensure a wide range of results to produce a good set of results, and a more accurate graph. Volume of liquids This will affect the rate of reaction, as large amount of mixture will take a long time to react, as I found in my preliminary work, and this will be impractical, the time in a practical being limited. If it is too little, the reaction is too fast. For this experiment I will use 5cm3 of each liquid. I found during the preliminary work that too much will mean the reaction last for too long, and too little a very short reaction. Stirring I will be important to stir the mixture to ensure that fresh amounts of catalase reach fresh hydrogen peroxide. Stirring will need to be consistent, as otherwise it can affect rate of reaction by making it slower when it is not stirred. ...read more.

Conclusion

Although slowly, hydrogen peroxide still decays in the absence of a catalyst (even in a fridge). This could affect the results. My control will be some yeast just left without any hydrogen peroxide. 2) Set the apparatus up in the way shown above. 3) Put the 5cm3 of 5% yeast into the flask, ensuring that it has been stirred first, using the syringe, and injecting through the special nozzle. Then zero the timers, and ensure that the gas cylinder is also at it's zero setting. 4) Inject the hydrogen peroxide, starting with 20%, and working downward throughout. Ensure that the syringe stays in place, in order to prevent gas release. Make sure that you start the stop clock as you inject the hydrogen peroxide. 5) Gently stir the flask, and ensure that stirring is constant. When the reaction has reached the stage where it has produced 30cm3 of gas, stop the stop clock, and then disconnect and wash out the tubing, flask and syringe, and anything else that could have come in contact with yeast or hydrogen peroxide. 6) Enter the results into the table, and if they prove to be inaccurate, repeat. Try and make sure that the repeats are done on the same day, as the conditions are likely to be similar, for instance position in the lab, draught e.t.c. Try and keep away from windows and doors in the first place, but if you have to be there, stay there for the duration. Nicholas Thorburn Block I NPTL ...read more.

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