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Effect of temperature and inhibition on the rate of pepsin digestion.

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Substrate Concentration Effect of temperature and inhibition on the rate of pepsin digestion K.Mukherjee, D. Sarpangal, E. Hsu., A. Choi, C. Han Monta Vista High School February 11, 1994 Abstract This experiment focused oil the role of temperature and inhibition in determining the digestion rate of the enzyme pepsin. In the experiment, pepsin in an HCl solution was used to digest the proteins found in egg whites. Different preparations, such as egg white and egg white with starch, were tested at three different temperatures. Our results yielded the conclusion that, of the temperatures tested, protein digestion using pepsin occurs most effectively at 37 C. Furthermore, we found that starch inhibits the activity of pepsin. Introduction One of the most important biological processes for animals is that of digestion. In humans, digestion begins in the mouth, where food is chewed and salivary amylase begins to digest carbohydrates. After food is swallowed, it is transported down the esophagus into the stomach, where digestion begins in earnest. The stomach's muscular walls help to break down food, as does the hydrochloric acid secreted by glands inside the gastric pits. Later oil, the intestines help to digest and absorb food. However, digestion Would not be possible without the presence of stomach enzymes. Various enzymes help to digest food in general, and in particular they are needed for the digestion of proteins. Proteins consist of chains of amino acids which form into three-dimensional shapes because of electrostatic attractions and repulsions between polar and nonpolar molecules. ...read more.


It can be further observed that pepsin was approximately 50% less effective digesting the starch-egg white mixture than the plain egg white. Discussion It can be seen frorn our experiment that temperature and inhibition affect tile digestion rate of enzymes. Theoretically speaking, a graph of enzyme activity versus temperature looks something like a bell curve; at very low temperatures, there is little enzyme activity. This lack of activity occurs because of the lack of kinetic energy; at lower temperatures molecules have less energy which can be contributed to the making of activated complexes. Thus, at lower temperatures tile overall rate of chemical reactions is very low. However, as the temperature increases, so does the rate of reaction and the rate of enzyme activity. Most enzymes have a certain temperature at which they are most effective [1]. For example, the enzymes in our gut bacteria, such as Eschericha coli, are most probably adapted to work most efficiently at a temperature of 37'C; thus incubators are usually set to this temperature when E coli is present as part of an experiment. As the temperature increases beyond tile ideal temperature for an enzyme, the hear results in additional kinetic energy which changes the shape of an enzyme and the electrostatic bonds between various molecules. As a result, the enzyme becomes less effective. As the temperature continues to increase, irreversible damage is done to the structure of the enzyme; it is denatured in the same way that egg proteins are when they are fried sunny side up. ...read more.


The starch could either "stick" to or encase the protein, making it difficult for the pepsin to cleave the protein's peptide bonds, or it could "stick" to the enzyme itself, directly interfering with its ability to catalyze reactions. To determine which, if any, of these theories actually explains our observations would require research into the structure of pepsin, egg white proteins, and starch, as well as additional observations based Oil Our Current experimental design. In addition to expanding the research oil inhibition, this experiment could be improved in several other ways. First, the results for the egg white-Na0H mixture could not be used in the experiment because, In two out of three water baths, the mixture diffused our of the capillary tubes and Was thus lost. In general, the NaOH created severe difficulties; it tended to form a gelatin when mixed with egg white, and as a result tile mixture was exceedingly difficult to place inside capillary tubes. Most probably, a weaker base, such as Ca(OH)2, would have to be used if tile experiment were redone. We could also use wider tubes in a future experiment. While using wider test tubes would require more egg white, starch, and base, it could make the cooking process much easier; Saran wrap could be used to cover the ends during cooking, preventing leakage. Even though our experiment call clearly be improved, it did yield some Conclusions. We determined that pepsin was more effective at 37'C than at room temperature or 0'C. We also determined that starch acts as an inhibitor of pepsin, thus creating all interesting field for future study. ...read more.

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** A report marred by poor experimental design and the failure to include several key sections vital for good coursework assessment.
To improve.
Research and rationale
The rationale for the experiment needs to be clearly justified in terms of its scope. The reasoning for the testing of starch as an inhibitor of pepsin needs to be discussed and relevant selected references added to justify the experiment.
It is not good practice to examine several independent variables at the same time. The candidate has varied temperature, substrate and pH within the same experiment and this would inevitably lead to confusion when interpreting the results. The choice of sodium hydroxide to alter the pH substantially alters the nature of the substrate meaning the results would be invalid. If the experimenter believed starch was an inhibitor then all the other parameters should remain the same ( with suitable controls tested). A pilot or trial experiment would have overcome the problems inherent in the method. The important variables to be controlled need to be described fully and the apparatus choice needs to be justified. A range for the independent variable was chosen but there is no indication as to why this range was chosen and no suggestion for repeating the collection of data. There was no risk assessment included.
Only nine pieces of data were planned to be collected and no results table was included which would mean this section would fail to gain credit.
Analysing and evaluation
No graphs were included in the report and statistical analysis was not possible when only six pieces of usable data was collected. There was an attempt to interpret the data using biological knowledge but the lack of data meant that the conclusion drawn is open to doubt. Some suggestions for improvements to the method were included but the problems inherent in the entire methodology would mean reliable results would be difficult to collect.

Marked by teacher Stevie Fleming 26/07/2013

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