The Importance of pKa in Determining Activity: A Brief Overview

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Discussion Overview

The discussion revolves around the role of pKa in determining enzyme activity as a function of pH, particularly focusing on the characteristics of the corresponding graphs. Participants explore the relationship between pH, pKa, and enzyme activity, with references to titration curves and points of inflection.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant explains that at pH equal to pKa, the concentrations of the ionic forms [A-] and [HA] are equal, and discusses how the slope of the graph changes with varying pH.
  • Another participant questions the relevance of the graph without seeing it, highlighting the need for clarity in the discussion.
  • A participant suggests that the graph may resemble a titration curve, noting that not all pH vs enzyme activity graphs follow this pattern and that they can take various forms, including bell-shaped curves.
  • Concerns are raised about the adequacy of the explanation provided, with a suggestion that it lacks depth and may require mathematical formulation to clarify the relationship between pH and enzyme activity.
  • One participant asserts that the point of inflection occurs at the halfway point of the maximum slope, where pH equals pKa.
  • Another participant expresses skepticism about the accuracy of the data presented, questioning the symmetry of the curve and suggesting that a model with multiple ionizing groups may be necessary.
  • There is a call for more context regarding the experimental setup, including the system, reaction, and measurement methods used.

Areas of Agreement / Disagreement

Participants express differing views on the adequacy of the explanation and the accuracy of the data presented. There is no consensus on the interpretation of the graph or the validity of the claims made regarding the relationship between pH, pKa, and enzyme activity.

Contextual Notes

Participants note limitations in the explanation, including the lack of a clear graph and insufficient detail about the experimental conditions. There are also concerns about the potential need for a more complex model to accurately describe the observed data.

mimi88
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Homework Statement
Explain why the pka important to activity can be determined from the point of inflection of the graph
Relevant Equations
ph=pka
My explanation is : for ph=pka , the number of two ionic forms[A-] and [HA] are equal,
then, for ph>pka,[A-]>[HA], the gratient gets smaller when ph is increased,
and also, for ph<pka, [A-]<[HA], the slope is becoming larger when pH is increasing .

Would u like to have a look of my explanation please.
 
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Point of inflection of what graph?
 
a ph vs enzyme activity graph, thanks
 
In agreement with Borek, the question is almost meaningless if you don't show the graph.

However I can psych that your curve looks similar to a titration curve.

Not all pH vs enzyme activity graphs look like a titration curve. They can look like two titration curves, back to back, or frequently a "bell shaped curve".

You asked us to have a look at your explanation. Assuming it looks like a titration curve I would say your explanation is not an explanation, it is a restatement.

Not just enzyme activity, but plots of many parameters that vary according to pH, for example optical absorbance (extinction coefficient) at constant wavelength, plot like a titration curve. Can you say why?

An ordinary titration curve has this same characteristic that the slope is maximum at the halfway point where pH = pK. So the main thing is if you can explain that. I don't think you can do it without bit of mathematical formulation.
 
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As my graph has shown, my explanation is : the point of inflection is at the half of the maximum slope, where pH=pKa?
 
Can you explain where this question comes from? Are these your own experiments?
The diagram is lacking even a horizontal pH scale. One would need that to even speculate.
We would need more detail but I doubt somehow that your data is accurate enough to be able to call that point a point of inflection.
The curve is not symmetrical, and I think that alone implies you'd need a model with at least three ionising groups. I doubt your data is good or extensive enough to get far with analysing that.
It would also be helpful if we knew what the system, the reaction, the measurement method is.
 

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