Isoelectric Point

Question 1

When is a protein said to be at their isoelectric point?

Answer 1

They have an overall neutral charge and precipitate out of solution

Question 2

What do the combined charges of the amino acids in a protein give the protein?

Answer 2

It’s overall charge

Question 3

What is the charge of the protein dependant on?

Answer 3

The pH of the solution it is in

Question 4

What kind of charge do proteins carry at a pH below their isoelectric point ?

Answer 4

Positive

Question 5

What kind of charge do proteins carry at a pH above their isoelectric point ?

Answer 5

Negative

Question 6

What does isoelectric focussing use?

Answer 6

A pH gradient to separate proteins according to their isoelectric point

Question 7

In isoelectric focussing, how is a pH gradient set up?

Answer 7

Along a tube of polyacrylamide gel using a mixture of special buffers.

Question 8

What happens during isoelectric focussing?

Answer 8

Each protein in the sample is loaded onto the gel and will move until it reached the pH corresponding to its isoelectric point. At this pH, the protein will move no further and form a band which can be visualised after staining