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... on to use ice and water baths, heated or cooled to different temperatures to achieve the correct temperature in the enzyme and substrate. 16. Plan for pH I am going to use the three categories of acid, neutral and alkaline to test how pH affects the rate of the enzyme rennin. Whilst studying the affects of varying the pH, I am going to ensure that all other variables are constant. Therefore, I will continue to use 2 ml of milk and 4 drops of rennin. The temperature I shall conduct these experiments at will be room temperature (27 C).
I have decided on this temperature because it is hot enough to provide the enzyme and substrate with enough energy for a successful collision and yet it is not quite ideal. For if it was the ideal temperature to have the rennin, the reaction would take place so fast that no significant difference between the various pH levels would be seen; for I have predicted temperature to have the greatest relative effect. To change the pH, I am going to put 2 drops of the following into the rennin: hydrochloric acid for acidic conditions (pH 1) water for neutral conditions (pH 7) sodium hydroxide for alkaline conditions (pH 10) I will mix the two together and leave for one minute to allow the pH to have an effect on the environment of the rennin. I am not going to put the acid, water or hydroxide into the milk because I know that the hydrochloric acid will begin the conversion of the caseinogen to paracasein before the rennin has been added. Also the milk will dilute the pH.
To see if this happens with any other pH, I am going to set up a control for each experiment where no rennin is added, but the pH of the milk is changed. I must ensure in this experiment that none of the substances mix through pipettes or thermometers otherwise my results will be inaccurate. I will then time, as usual, the length of time it takes for the milk to clot. 17. Plan for Concentration of Enzyme To investigate how the concentration of enzyme affects the rate at which it works I am going to vary the number of drops of rennin I add to the milk. However, to keep the volume of the liquid the same I will make up the rest with drops of water. number of drops rennin water 4 0 100 % enzyme 3 1 75 % enzyme 2 2 50 % enzyme 1 3 25 % enzyme 0 4 0 % enzyme I will again use 2 ml of milk; have everything at a temperature of 27 C; leave the milk and rennin in neutral conditions.
This is so that the reaction is not completed so fast that I cannot measure it, and also to ensure the effects are purely due to the concentration of the rennin. 18. Accuracy To ensure that my results are accurate I am going to conduct each of these experiments twice. RESULTS 19. Temperature The table shows the results I collected when I altered the temperature. I was only able to get results from this experiment at two temperatures (20 C and 40 C).
Above these no reaction occurred at all which suggests that the heat had denatured the rennin. Below 20 C at freezing point I was forced to stop timing due to the limitations of time. The milk had begun to clot but had still not finished after 50 minutes. 20. pH The table shows the results I collected when I altered the pH. 21. Concentration of Enzyme The table shows the results I collected when I altered the enzyme concentration. CONCLUSIONS 22.
How Temperature Affects the Rate of Rennin The fact that I only achieved results at two temperatures shows that rennin is greatly affected by variations in temperature. here is also a vast difference between the time of reacting for 40 C and 20 C - 21. 95 minutes in fact. This shows that, as I predicted, rennin's optimum temperature is round about body temperature. This is the temperature when the conflicting influences of increased rate of reaction due to increased heat energy and the decreased rate of reaction due to the denaturation of the rennin is most balanced. For at 40 C, the rennin has sufficient energy, due to the heat, to have increased kinetic energy as do the milk molecules. Thus with the faster movement more collisions will take place, and as the enzyme and substrate have high energy there is a greater chance of there being enough energy to reach the activation energy and for the conversion to take place.
However at 40 C the enzyme is not (or is only mildly) affected by the destruction of its hydrogen and ionic bonds by the heat. When they are broken the shape of the active site is changed and the caseinogen will no longer fit into the site and the reaction stops, therefore the rennin is said to be denatured. I believe this to have occurred at the temperatures 60 C and 80 C. The measurement for 20 C is so much longer than that for the optimum temperature of 40 C because again of the kinetic and collision theories. For the reduced heat reduces the amount of energy the molecules are receiving.
This decreases their kinetic energy, ie their movement slows, which in turn decreases the amount of collisions between enzyme and substrate, and increases the likelihood that there will not be enough energy for the reaction to take place when the rennin and caseinogen collide. Therefore the rate of reaction reduces. I expect that at 0 C the rennin and caseinogen had such a lack of energy that it would have taken them a long time to react together. I stopped timing at 50 minutes, but I believe the milk would have eventually fully clotted for I could see that it had already begun to do so.
My results are as I predicted with rennin being denatured at high temperatures and being unable to react at low ones. However, I did not realise how small the range of temperature was that it works in. For reacting milk and rennin at temperatures other than about 40 C is very uneconomic due to the time it takes to clot. So 40 C appears not only to be the optimum temperature at which the rennin works but nearly the only temperature at which it achieves the conversion of caseinogen to paracasein.
It is due to this that I now realise how important it is for babies to be fed milk that has been gently heated so that the rennin in their stomachs will work successfully. If I was able to do this experiment again I would like to make the range of temperatures even smaller, especially by breaking down the range 20 C to 40 C into maybe 5 C intervals. This would enable me to achieve an even more specific and accurate temperature at which rennin works to its optimum. The table shows that the results for the two times I did the experiments were very similar and so I can say that my experiment was fairly accurate, within experimental limitations. 23.
How pH Affects the Rate of Rennin I can see from my results that the rennin is completely denatured by alkali conditions, as predicted. For this pH has altered the bonds in the enzyme which help the rennin keep its shape. Thus when these bonds are altered the shape of the active site of the rennin changes which prevents the substance fitting into it, which prevents the reaction taking place. I can see that the rennin does work in neutral conditions, but not as quickly as when it is in acidic ones.
This is as predicted because the gastric juice in the stomach contains a lot of hydrochloric acid and this is where rennin is produced. I believe that rennin is not denatured by neutral conditions, because rennin has to be able to work when the acid in the stomach is diluted by food and other liquids. Also milk is of a neutral pH, so if rennin was denatured by such, problems would occur. Also neutral is not an extreme pH, as alkali is, and so is closer to an acidic pH. The control shows that hydrochloric acid breaks the milk down, unlike water or sodium hydroxide, without the need for rennin.
However clotting does not occur as quickly without the catalyst. This was to be expected because as mammals mature the production of rennin is reduced and it is left primarily to the acidic gastric juice to convert the milk protein. This experiment proves that the rate of rennin is affected by varying the pH, and that its optimum working pH is acid, pH 1. If I had had more time I would have liked to dilute the acid to achieve a range of pH between 1 and 7. this would enable me to see how smaller changes in pH affect the rate of reaction.
The problem with this experiment is that though I know the rate of reaction to be best at pH 1, from the control I also know that acid itself breaks up the milk. Therefore, how much my result is the increased rate of the rennin due to the acid or how much is due to the acid itself converting the caseinogen to paracasein I cannot be certain. However, it took a much longer time for the acid to clot the milk without the rennin, which shows that when it was added the rennin was a lot more active and successfully catalyst the reaction. From my table I can see that the results of the initial and repeat experiments were very similar, suggesting that both were fairly accurate. 24.
How the Concentration of Enzyme Affects the Rate of Rennin I can see that as predicted the highest concentration of rennin produced a clotting in the shortest amount of time and therefore had the highest rate of reaction. My results show no sign of the presence of the limiting factor, meaning that there was still enough substrate for the enzyme to act on in the maximum concentration. In a further experiment I would like to increase the ratio of rennin to milk until I can tell that all substrate is occupying an enzyme molecule, and the addition of more rennin would have no effect. As the concentration decreases so does the rate of reaction, as I predicted, for it takes more time for the fewer numbers of rennin molecules to convert all the milk molecules. As in my prediction the concentration of the rennin will not completely stop the experiment (unless it is not there as in 0 % conc. ) because rennin is not affected by the reaction it catalyses, so it can be used over and over again. However, in the smallest concentration I was forced to stop timing because the reaction was taking so long.
I feel it is important to note that if the rennin had been heated to its optimum temperature of 37 C to 40 C, even in that small concentration it would have had the ability to move faster and collide more successfully and therefore would have clotted the milk at a faster rate. A limitation with this particular experiment is that the volume of liquid in each pipette drop can vary slightly, so the results may not be truly accurate. 25. Overall Conclusion From the results and conclusions of the three independent experiments, I am able to state that the ideal working conditions for rennin is in a temperature of 40 C, in a pH of 1 and in a maximum concentration of enzyme. I believe that my predictions were correct and temperature does have the greatest relative effect; for the concentration of rennin will not completely stop the reaction or dramatically increase it, because enzymes can be used over again. pH is a very important factor because in alkaline conditions the enzyme is denatured and the difference in reaction times between neutral and acidic conditions are quite great. However, by looking at the results for temperature I can see that it causes the reaction to stop above 40 C because the enzyme is denatured and below 20 C it has the effect of slowing the reaction dramatically and so I was unable to measure it.
The considerable difference between the times for 20 C and 40 C suggests to me that just small variations in temperature have great affects on the rate of reaction. The primary limitation with this experiment was the judgement by eye of when the milk had fully clotted, as this is not going to be completely accurate and the same for each experiment. I considered conducting the experiment in another way, but as no gas, which I could collect for example, was produced, the only other way was to weigh the amount of curds and whey created. However, with thought I reasoned that the factors I was testing would not affect the actual amount of curd produced, just the speed at which it was produced. If I was to do this investigation again I would use more detailed and smaller ranges of readings because for many of the experiments I got no result, as it appears rennin is very specific in its ideal conditions. To conclude I have found rennin to be denatured in alkali conditions and / or temperatures over 60 C, but as predicted, to work best at 40 C, at pH 1 and with the maximum amount of the enzyme possible.
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