Solve Braford Assay: Why is My Answer 20X Different?

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Discussion Overview

The discussion revolves around a homework problem related to the Bradford Assay, specifically addressing a discrepancy in calculated protein concentration. Participants explore the reasons behind a significant difference in their results compared to the expected answer, examining the implications of sample volume and dilution factors.

Discussion Character

  • Homework-related, Technical explanation, Debate/contested

Main Points Raised

  • One participant calculates a protein concentration of 0.00842 µg/µl based on an absorbance value of 0.562 and a calibration equation but finds this differs from the expected 0.168 mg/ml.
  • Another participant suggests that the absorbance value used may not correspond to the original solution, implying a potential misunderstanding of the assay setup.
  • A different participant recalls a detail about a 0.05 ml sample, speculating that the factor of 20 difference might relate to this dilution.
  • One participant points out that while the calculated answer differs by a factor of 20, the units of measurement (µg/µl vs. mg/ml) complicate the comparison.
  • Another participant clarifies that the total volume of the assay is 1000 µl, leading to a calculation of total protein mass based on the initial concentration.
  • A later reply confirms the dilution factor, stating that 50 µl of the sample was diluted to 1000 µl, which aligns with the calculations presented.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the initial absorbance value and its relation to the calculated concentration. There is a general agreement on the dilution factor but differing interpretations of how it affects the calculations.

Contextual Notes

Participants reference specific volumes and dilution factors, but there is some ambiguity regarding the initial conditions of the assay and how they relate to the final concentration calculations.

Who May Find This Useful

This discussion may be useful for students or individuals working on protein assays, particularly those using the Bradford method, who are encountering similar discrepancies in their calculations.

tvtokyo
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Homework Statement



https://www.physicsforums.com/attachments/76905
https://www.physicsforums.com/attachments/76906

Homework Equations

3. The Attempt at a Solution [/B]
Hi I have a question on Braford Assay:
I am given this question:
I did the caluclation as follows:
y = 66.717x
Since given absorbance = 0.562
0.562 = 66.717x
x = 0.00842ug/ul
But the answers given is 0.168mg/ml
I do not know what I did wrongly? Can anyone please help? Thanks!
My answer and the correct answer differ by a factor of 20? Why is that so?
 
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tvtokyo said:
My answer and the correct answer differ by a factor of 20?

0.562 is not absorbance on the original solution.
 
Yes, I was trying to answer this question but when I press your links this time I am told I don't have right to access the page. But I remember when I saw it before there was something about an 0.05 ml sample - which is 1/20 of an ml. Could these occurrences of 1/20 be in any easy connected?
 
I still don't get it though. Sorry. I will post the image again, Sorry for the trouble pal!
Anyway, even it is a factor of 20. My answer has a unit of ug/ul and the correct answer is in mg/ml so technically it is not a factor of 20??

upload_2014-12-26_10-21-24.png

upload_2014-12-26_10-21-47.png
 
Please reread the last paragraph of the attached text, it clearly tells you why the difference is 20.

50+750+200=1000.
 
I am suppose to find the protein concentration of the liver sample what do i do with the 1000ul ?
Is this correct?
Since x = 0.00842ug/ul and total volume of my assay --> 1000 ul
Then mass = 0.00842 * 1000 = 8.42 ug
Concentration of protein = 8.42ug/50ul (of protein in liver)
= 0.1684 ug/ul = 0.1684 mg/ml
 
Correct.

50 μl of your sample were diluted 20 times to 1000μl.
 
Thank you!
 

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