Key Factors: We could change:
- Temperature
- Amount of Pepsin
- Amount of Egg White
We are going to be changing only the temperature in this experiment. The other two parameters are going to be kept constant to keep the experiments fair tests. This is important because if thy weren’t kept at a constant my conclusion could be wrong, and so my graphs.
Method: We are going to first set up a 100ml beaker about half full with water at a required temperature, 20oC, through to 60oC, at 10oC intervals. Then we are going to add 2cm3 egg white, 2cm3 pepsin and 2 drops of hydrochloric acid, so the pepsin will be at pH1 its best working condition, to a test tube and put this in the water bath. We will have beakers containing hot and cold water to add to them if needed to keep them at the required temperatures.
We will be measuring the time it takes for each solution to turn clear, repeating the experiment three times, and then taking the averages. All the information will be recorded in a table.
Equipment:
Results:
In the graph I have drawn 1/time, the inverse of time, so that the graph will be an indication of rate of reaction, and if the prediction was right, the graph should give a curve which will initially rise and then fall back down.
Conclusion: From my results, I can just about draw a good conclusion, that the enzyme reached its optimum temperature at 40oC. However, when doing the experiment at 60oC, the experiment went very quickly, which was out of line with the others. However the rest of the curve seemed to go up, reaching its high point at 40oC, and then starting to come back down.
This is because the enzyme works best at 40 oC, because the enzyme was moving about quickly and was able to react with lots of the substrate. Below this, the enzyme didn’t have as much energy, so will not react as fast. Above this temperature, the enzymes start to vibrate because of the amount of energy they have, and then starts to change shape. When this happens, the substrate, which is shaped specifically for that particular enzyme can’t fit into the enzyme (the “lock and key” hypotheses), so the enzyme will not work. When this happens, it means the enzyme has denatured.
In this experiment, the enzyme pepsin broke down the protein, the egg white into amino acids. This was the white precipitate we were left with was the amino acids, which looked more like egg white, than the solution we began with!
The enzyme pepsin likes a low pH, dissimilar to other enzymes, so that’s is why the hydrochloric acid was added. This is a lot like human stomachs, where a lot of acid is present. Pepsin in the human body starts life as pepsinogen, an inactive enzyme which is turned into to pepsin to react with proteins. If it was produced as pepsin, it is so powerful, it would start to break down the tissues in our body! The digestion process is quite slow in human bodies, which could explain why the reaction took a while to happen.
Evaluation: I think this experiment went quite well, although because of the nature of the experiment, collecting results was difficult, as the investigations took a while to start working and finish working. However, we worked quite well as a group, and did eventually manage to get a few results. Even though, our results from the 60oC experiment did not seem to fit the pattern on the graph.
One explanation for these anomalous results could be to do with the enzyme, and its temperature. In the experiment we first warmed the water baths to the right temperature, and then put the test tubes in. This meant that while it was being warmed, the enzyme was reacting with the egg white, until it got so hot that it denatured, instead of being denatured before the experiment started. This could have affected our results, and if I was to do the experiment again, I would allow time to heat the pepsin to the required temperature
Another factor that could have affected our results was the temperature of the water baths. Trying to keep them at the right temperature throughout the experiment was difficult, and this meant they dropped below their required temperatures. When this happened the enzyme began to work slightly better or worse, meaning the results became inaccurate.
We were short of time during the investigation, so it meant that we use several water baths all at the same time. If I were to repeat the experiment I would take more care to check the temperatures of the baths more regularly, or just do one at a time.
Measuring when the experiment had actually finished was again difficult. As the precipitate was formed, it started to settle, leaving a clear liquid behind. However, the some of the precipitate floated to the top and it meant we probably took a finishing point at different stages in each experiment. This could have again affected our results.
If I was going to repeat the experiment, I would definitely take more time and care over the temperatures of the experiments and before I started I would determine a finishing point which would be the same for each experiment. If I had the time I would do each experiment separately and repeat it a few times. This would mean I would get more accurate results which would probably make a better fit with the expected results.
To extend the experiment, I could extend the range of temperatures we took measurements at. If the temperature goes much beyond 60oC, I don’t think much would happen, but I could take it down to 0oC, using ice. We could also take measurements at every 5oC, so the resulting curve would be more accurate, and I would be able to draw a firmer conclusion. I could also test out other enzymes with their substrates, say amylase and starch, to see if temperature had the same effect on them.
