Question

is it possible to run a protein (size of 300kDa) and BSA (size of 66kDa) at the same time with 7.5% polyacrylamide gel? why or why not?

Answer 1

Polyacrylamide gel electrophoresis seperates proteins based on their size.
The migration distance of a protein in the PAGE gel is inversely proportional to its size.
i.e. larger proteins migrate slower as compared to smaller proteins.

The resolution power of a gel is directly proportional to the percentage of the gel.
i.e. high percentage gels can be used to distinguish two proteins that are similar in their size.

In the given case, two proteins significantly differ in their size. So, 7.5% gel can be used to separate them.
However, the BSA band would be at the lower end of the gel while the other protein would be at the upper end.

If the gel length is smaller, BSA would run out of the gel by the time the other protein enters the mid-stage of the gel.
So, ensure that the gel is sufficiently longer to accommodate both bands.