Question

What does SDS- PAGE do? Why is measuring molecular weight valuable? How to pick PA gel density?

Answer 1

SDS-PAGE stands Sodium Dodecyl Sulfate PAGE ( Polyacrylamide Gel Electrophoresis)

It is a technique for seperating proteins on the basis of their Molecular weight using a polyacrylamide gel as medium amd SDS as denaturing agent. SDS adds Sulfate to the protein invariable to all amino acids so that the entire protein gets a negative charge supporting it's movement in the electric field of the gel. The proteins move to the posotive electrode. Heavier proteins move slower through the gel, and hence are precipitated higher as compared to proteins with lighter molecular weights. A ladder is also run on the gel alongside the protein mixture which acts as a standard.

It is important to measure molecular weight as it can help us estimate the number of residues. Also a lot of transportation of proteins in the cell have a limiting and a threshold molecular weight. Heavy proteins can not easily permeate a membrane and need tranport channels and carriers. Molecular weight hence can help us identify the protein and its propoerties.

Density of gel determines the pore size of the gel. To seperate and identify proteins with a smaller molecular weight will require a smaller pore size which is a property of higher density gels. On the other hand of we want to identify proteins with a higher molecular weight pore size can be high and the density of gel can be low. This is how we can control the density of PA gel as per our requirements.

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