Gel electrophoresis question

[gangazi]

Does Gel Electrophoresis separate molecules based on size and charge or size and shape?
and when you use SDS-Gel Electrophoresis, you separate molecules based only on size because they all have negative charge? or do you also separate based on size and shape

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[rdub]

SDS-page is a detergent that will give all proteins a negative charge so that they will migrate in a electric field according to their molecular weight. If you put proteins on a gel without SDS, the proteins all have different charges and so their movement will be affected by both size and charge.

If you are doing electrophoresis with DNA, then you don't need SDS because DNA is already negatively charged. It doesn't separate them by charge because they all have the same charge. The only way it can separate the DNA is by size/shape

 

[gangazi]

SDS-page is a detergent that will give all proteins a negative charge so that they will migrate in a electric field according to their molecular weight. If you put proteins on a gel without SDS, the proteins all have different charges and so their movement will be affected by both size and charge.

If you are doing electrophoresis with DNA, then you don't need SDS because DNA is already negatively charged. It doesn't separate them by charge because they all have the same charge. The only way it can separate the DNA is by size/shape

Crystal clear thank you!

 

[gangazi]

ok so nucleuic acid is DNA/RNA so they are negatively charged so I picked A but now its A and B?! ugh

 

[gangazi]

@orgoman22 needs to come rescue us

 

[DAT Destroyer]

@orgoman22 needs to come rescue us

He will respond soon, where are these problems coming from?

 

[gangazi]

He will respond soon, where are these problems coming from?

kap test and datqvault! thank you!

 

[FutureDDS_11]

Here is my take:
During Gel Electrophoresis, nucleic acids (negative because of phosphate group) start at the negative end which repels them towards the positive end. Since those that are smaller can travel faster through the gel (bigger ones left behind), it separates them based on size. In addition, size and charge are related (because different size = different number of the charged phosphate groups = different charge), which is why I think charge is also a correct answer (even though the charge separation might be very slight).
I think about it like this: fragments that didn't travel as far to the positive end means that they were not as negatively charged (therefore more positively charged) as the smaller fragments which means the smaller ones were more attracted to the positive end.

Hope this helps.