Protein migration in SDS gel - why? (May/11/2006 )

Hi everybody,
why proteins are running from cathode to anode in SDS-PAGE,although the proteins are neutral in charge
thank you

hi
entering the gel, the proteins are surrounded by SDS molecules that confers them a negative charge.
Entering the pH 8.8 part of the gels, the proteins are more negative.

the proteins are not neutral in charge unless they are at their isoelectric point (pI), with sds they will carry a negative charge even at the pI. without the sds, most proteins would have a net negative charge at the pH of a sds gel (without the sds or with). the sds theoretically imparts an equivalent (negative) charge density to the proteins so that they will be separated strictly by size.