Section Bank B/B #45

[betterfuture]

If the question stem suggested that PKA and GSK-3 are shown to autophosphorylate, then how come in the control we don't see any bands? Is it because the samples contain CREB327 and the control doesn't? If so, I always thought controls are supposed to address the focus of the experiment, which is the the protein CREB327?

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[theonlytycrane]

There's a band at the bottom in the control lane that also appears in all of the other lanes. The ATP is radio labeled so if CREB isn't phosphorylated it won't show up (as in the GSK-3 only case).

 

[betterfuture]

Well then

But aren't experiments supposed to have controls that deal with what they are testing? I would have thought they would include CREB in there. I was getting contradicting things from EK FL4 so I wasn't sure.

 

[theonlytycrane]

It depends on the setup. In this case, the radio-labeled ATP is used to get some idea about CREB phosphorylation. We wouldn't want to misinterpret auto-phosphorylation by PKA or GSK-3 as CREB-phosphorylation so based on the question stem it makes sense.

I think choice (A) would be another valid control, but it's less hinted at by the q-stem. Choices (C) and (D) are out because without ATP, no label would be detected in either case.

 

[betterfuture]

So in this case, they want a positive control? One where ATP is detected?

 

[laczlacylaci]

So in this case, they want a positive control? One where ATP is detected?

Wouldn't this be a negative control, since nothing showed up? Sorry to barge in mid-way convo.

 

[betterfuture]

From the figure, there seems to be a band at the bottom of every lane. I totally ignored that since I was confusing it with wells. Since PKA and GSK-3 autophosphorylate, and since ATP was added, and they are tagging ATP and trying to detect its presence, my guess would be this is a positive control since positive implies a treatment where results show up as expected. The expected being the band showing up under autoradiography to show ATP presence.

 

[laczlacylaci]

From the figure, there seems to be a band at the bottom of every lane. I totally ignored that since I was confusing it with wells. Since PKA and GSK-3 autophosphorylate, and since ATP was added, and they are tagging ATP and trying to detect its presence, my guess would be this is a positive control since positive implies a treatment where results show up as expected. The expected being the band showing up under autoradiography to show ATP presence.

Ah, completely ignored the bands near the +, and only focused on the stuff near-.