DNA Supercoiling

[Onlygoodinmath]

A question on a quiz read:

Which of the following DNA molecules would migrate the fastest in an electric field?

A. 1000 bp linear fragment in a agarose gel
B. 1000 bp linear fragment in a 0.7% agarose gel
C. 1000 bp supercoiled plasmid in a 1% agarose gel
D. 1000 bp supercoiled plasmid in a 0.7% agarose gel
E. 1500 bp linear fragment in a 1% agarose gel

I narrowed it down to C or D, but I do not know how the concentration of the gel affects the migrating speed. Can someone explain that to me.

[canalon]

The agarose forms a gel a web of entangled molecules. The DNA moves within this web. The smaller it is, the easier it is to move within the matrix, as you already know, but increasing the agarose content is just like increasing the density of the web. What do you think is the effect on the speed of migration?

[Onlygoodinmath]

So... increasing the agarose concentration makes it harder for the DNA to travel through the gel. So then, its obviously D.

Thanks. I appreciate the help.

[JackBean]

Yeah, that's right