In this question, I am asking you to think about the sensitivity of gel electrop

Question

In this question, I am asking you to think about the sensitivity of gel electrophoresis and staining. How many copies of a protein need to be present in a typical eukaryotic cell in order for it to be visible as a band on a gel? Assume that you can load 100 ug of protein in a lane, and that the faintest band you can detect is 10 ng (by silver staining). The concentration of protein in a cell is about 200 mg/mL, and a typical eukaryotic cell has a volume of about 1000 um3 (1 picoliter). How many copies of a 120 kD protein would need to be present in a cell in order to be detectable?

Explanation / Answer

1 kD of protein is equal to 1.66053904 X10-18 milligrams in weight.

Using this to find the weight of 120 kD protein in milligrams we get

120 X 1.66053904 X 10-18 milligrams

= 199.2646848 X 10-18 milligrams

Since the concentration of protein in a cell is about 200 mg/ml therefore, the number of copies of a 120 kD protein present in cell will be:

200/ 199.2646848 X 10-18

= 200 X 1018 / 199.2646848

= 1.0036 X 1018 copies

Thus, 1.0036 X 1018 copies are needed of 120 kD protein in a cell to be detectable.

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