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Modifying a simple hydrolysis of sucrose experiment to measure Michaelis Menten constant for the dextrase content of yeast

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Introduction

Investigation: Modifying a simple hydrolysis of sucrose experiment to measure Michaelis Menten constant for the dextrase content of yeast David Biology SL Aim: How can the Michaelis Menten constant for the dextrase content of yeast be calculated with simple experiment on hydrolysis of sucrose? Introduction: In anaerobic conditions yeast cells break down sugar molecules into ethanol and produce carbon dioxide. The process is called alcoholic fermentation. The equation of this process is: C6H12O6 -> 2 C2H5OH + 2 CO2 ↑+ E. The process consists of a series of reactions catalyzed by specific enzymes. The enzymes present in yeast cells are specific, i.e. they will catalyze the fermentation of certain sugars but not others. Michaelis–Menten kinetics is one of the simplest and best-known models of enzyme kinetics. The model takes the form of an equation describing the rate of enzymatic reactions, by relating reaction rate to , the concentration of a substrate S. Its formula is given by ( http://en.wikipedia.org/wiki/Michaelis%E2%80%93Menten_kinetics) Independent variable: Different concentrations of sucrose(%)(range: 0.0% (Distilled water), 0.5%, 1.0%, 5.0%, 10.0%, 20.0%) Dependent variable: Height of the suspension-sugar level(cm)(range: 0~) Controlled variables: Temperature(°C), heat treatment length(seconds), concentration of yeast suspension(%) Hypothesis: Hydrolysis of different concentration of sucrose and graph’s tangent would make able to predict the calculation of the rate of reaction. Materials and methods: Materials: 6 fermentation tubes 6 test tubes Saccharomyces fungus suspension (20%) Different concentrations of sucrose: 0.0% (distilled water), 0.5%, 1.0%, 5.0%, 10.0%, 20.0% Stirring rod Glass marker Semco pipette Water bath Ruler Stopwatch ________________ Methods: Label 6 fermentation tubes 1 – 6 with a wax pencil so that experimenters can distinguish clearly. ...read more.

Middle

over 16 minutes. 0.0% concentration of sucrose means that the solution is plain distilled water without any sucrose concentration. The height has been measured with a ruler with uncertainty ±0.05cm every 240 seconds. I expect 1bout 10seconds of uncertainty between each time intervals. Because to avoid accidents such as breaking the test tubes, I placed 2 test tubes into water bath at a time which would have caused some time differences between each test tubes, and also, I took 2 test tubes out from water bath at a time, which would also have caused additional time differences between each test tubes.The results are from the third trial Height change of solution over time(±0.05cm) Sucrose concentration Time(±10secs) 0.0% 0.5% 1.0% 5.0% 10.0% 20.0% 0 6.80 6.80 6.70 6.80 6.80 6.90 240 6.80 6.70 6.70 6.50 6.50 6.70 480 6.80 6.70 6.40 5.20 4.80 4.90 720 6.80 6.40 6.00 3.40 3.00 2.40 960 6.80 6.20 5.70 1.20 1.00 1.40 Processing raw data: Table.4 Table 4 shows the processed data from Table 1. To find the Michaelis-Menten constant, I included the value of biggest change in height for each concentration of sucrose. The uncertainty of the value (±0.1) was calculated by adding two uncertainties (±0.05) together, thus getting ±0.1 as the answer. Height change of solution over time(±0.05cm) Sucrose concentration Time(±10secs) 0.0% 0.5% 1.0% 5.0% 10.0% 20.0% 0 6.40 6.90 6.70 6.90 6.80 6.80 240 6.40 6.80 5.60 6.40 5.60 6.00 480 6.50 6.90 4.90 3.80 2.00 3.30 720 6.60 6.70 4.50 1.50 0.40 1.40 Value of biggest change in height (±0.1cm) ...read more.

Conclusion

it is not very accurate and it is hard to measure them because sometimes the fermentation tubes are covered with the solution went out which would make it hard to read. Forth, the limitation of space for water bath for everyone to carry out the experiment caused us to have very limited amount of trials and sometimes, I had to wait until somebody take out their test tubes, which could?ve cooled down the solution, causing unreliability in data, and making us unable to have more data to make data reliable. Last of all, as you can see from Table.2, the solution with 10% concentration of sucrose hasn?t shown any changes after 960 seconds. It is occurred because the tube with 10% concentration of sucrose has broken by human mistake. So it might have brought a bit of inaccuracy data. Ways of improvement: While carrying out the experiment, I found that when I had my test tubes in the water bath, some people moved my test tubes around. This might also cause some errors in my results, so if this problem can be fixed, the data collected will be more reliable. This problem can be solved by having more space in room available for more water baths so each person can use their own water bath. In my opinion, further investigations can be performed by making controlled variables listed above such as the concentration of yeast suspension changeable and perform the experiment, using that as the independent variable. This might bring out some interesting and different results than the experiment. ...read more.

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