Effect of changing pH of pepsin on hydrolysis

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Discussion Overview

The discussion centers on the unexpected results of an A2 biology coursework experiment investigating the effect of pH on the hydrolysis rate of pepsin using milk protein. Participants explore potential reasons for the observed anomaly where a higher transmission percentage was recorded at a neutral pH compared to an acidic pH, contrary to expectations based on pepsin's known function in acidic environments.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant notes the expectation that pepsin should exhibit a faster hydrolysis rate at pH 2.8, as it functions in the stomach, but the results showed a mean transmission percentage of 9% at pH 2.8 and 15% at pH 7.0.
  • Another participant questions the chromophore used for measurement and whether its extinction coefficient could vary at different pH levels, suggesting this might affect the results.
  • Concerns are raised about the clarity of the milk protein solution at different pH levels, which could influence transmission measurements.
  • One participant emphasizes the importance of scientific integrity, criticizing the suggestion to falsify results and highlighting that experiments may not always yield expected outcomes.
  • There is a discussion about potential experimental errors, such as switching of samples or reagents, which could lead to incorrect results.
  • Another participant raises the possibility that the pepsin could have acted on itself if the solutions were prepared in advance.

Areas of Agreement / Disagreement

Participants express varying opinions on the validity of the results and the appropriateness of the teacher's suggestion to flip the data. There is no consensus on the reasons for the unexpected findings, and multiple competing views regarding experimental integrity and potential errors remain.

Contextual Notes

Participants note the limitations of the experiment, including potential issues with the preparation of solutions, the timing of the experiment, and the specific indicators used for measuring transmission. These factors contribute to the uncertainty surrounding the results.

Who May Find This Useful

This discussion may be of interest to students and educators involved in biology experiments, particularly those exploring enzyme activity and the effects of pH on biochemical reactions.

petey
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Hi,

Did my A2 biology coursework. I compared the rate of hydrolysis between pepsin 2.8 and 7.0 using milk protein. Pepsin works in the stomach, so should have a faster hydrolysis rate in the acidic pH value. But when I measured transmission percentage I got a mean of 9% for 2.8 and 15 for 7.0 pH. My teacher had no answer, and suggested flipping the results, but I think this is dishonest and feels wrong. What reason/s could there be for this anomaly?

Many thanks,
 
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What chromophore were you measuring? Did you measure the transmission percentage at pH 2.8 and compare it to the transmission percentage measured at pH 7? Could the extinction coefficient of the chromophore have a different value at those two pH's? Was the milk protein solution cloudy at one pH and clear at another?
 
petey said:
Did my A2 biology coursework. I compared the rate of hydrolysis between pepsin 2.8 and 7.0 using milk protein. Pepsin works in the stomach, so should have a faster hydrolysis rate in the acidic pH value. But when I measured transmission percentage I got a mean of 9% for 2.8 and 15 for 7.0 pH. My teacher had no answer, and suggested flipping the results, but I think this is dishonest and feels wrong. What reason/s could there be for this anomaly?

Many thanks,
Good, shows you have scientific mentality. What is the point of experiments if you force and falsify results?
Experiments do not always come out as they 'should', especially if you do not have time to find out why.
What was the buffer?
 
chemisttree said:
What chromophore were you measuring? Did you measure the transmission percentage at pH 2.8 and compare it to the transmission percentage measured at pH 7? Could the extinction coefficient of the chromophore have a different value at those two pH's? Was the milk protein solution cloudy at one pH and clear at another?
Indeed, this has come up with other similar kinds of experiments. What indicator is being used and what does an increase in transmission actually mean in terms of that indicator?

epenguin said:
Good, shows you have scientific mentality. What is the point of experiments if you force and falsify results?
Experiments do not always come out as they 'should', especially if you do not have time to find out why.
What was the buffer?

Great point too! It is unfortunate for a teacher to simply recommend switching the results. Though, I will point out that from an educational perspective (rather than a truly experimental one), I've had days when equipment was malfunctioning or reagents were improperly prepared and nobody got the results they should have gotten for an "experiment" that should have a known outcome...in those cases, I've provided data to the class to use in preparation of their reports that was different from what they obtained, but that was recognizing they did the best they could and something known to me but not them had gone wrong. Under ideal circumstances, they'd have repeated the experiment and checked for such malfunctions, but limited class time is rarely an ideal circumstance.

So, on one hand, it is good to consider if there is an explanation for seemingly contradictory results relative to predictions, and on the other hand, the teacher may be aware of something that went awry and it would be better from a pedagogic perspective to simply do as the teacher recommended and switch the values (maybe s/he realized afterward that two reagents were switched, for example).
 
My teacher had no answer, and suggested flipping the results,

Perhaps my English fails me, but it sounds a little bit ambiguous to me. Were you suggested to flip the results (i.e. falsify your data), or were you suggested that some experimental error could lead to flipping samples/results (i.e. data is already wrong)?

Borek
 
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Yes e.g. solutions or labels could get switched.

I have just though, were solutions made much before? Could the pepsin have worked on itself? Does it?
 

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