TBR Ch8 Electrostatics

[bdc142]

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Hi,
Can someone explain #10 on page 144? (Question about electrophorsis).

I don't get why the bands wouldn't just run off towards B+ aka answer B: The bands ran diagonally off the gel's left side.

Thanks!

 

[bdc142]

TBR's answer is that:

If you load an agarose gel backwards (aka wells are at the positive electrodes), there won't be ANY migration of DNA at all.

Can anyone tell me why?

 

[chiddler]

TBR's answer is that:

If you load an agarose gel backwards (aka wells are at the positive electrodes), there won't be ANY migration of DNA at all.

Can anyone tell me why?

i'm not looking at the same figure you are so not sure if this will help, but in the lab, loading the gel backwards would cause the band to ruck backwards. since there isn't much room for backwards movement, it'll quickly be run off the gel into solution.

 

[bdc142]

i'm not looking at the same figure you are so not sure if this will help, but in the lab, loading the gel backwards would cause the band to ruck backwards. since there isn't much room for backwards movement, it'll quickly be run off the gel into solution.

Yeah that's what I thought too. I guess TBR is wrong.

 

[Dasypus]

I don't have the passage in front of me, so I'm a bit confused, but I'd like to understand what's at stake here. DNA is negatively charged. If you load it right next to something positive, it should be attracted to it and hang tight, right?

 

[bdc142]

I don't have the passage in front of me, so I'm a bit confused, but I'd like to understand what's at stake here. DNA is negatively charged. If you load it right next to something positive, it should be attracted to it and hang tight, right?

Yeah, so I guess this question was just nitpicky: it asks 'why doesn't the scientist see bands migrate properly?". I said it was because it ran off the wrong way (because the electrode placements are on the opposite side). The answer is because the scientist put the wells on the wrong side.