Official Guide C/P #19

[kryptonxenon]

Can someone explain #19 of the C/P section in the Official Guide? Here is the question:

A scientist proposed that the 32P label was entering PE molecules by direct exchange (swapping phosphate groups with those found in solution) and NOT through synthesis of new PE by bacterial cells. What experimental modification can show this is NOT the case?

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[theonlytycrane]

If the 32P was incorporated into the membrane by direct exchange instead of through synthesis, acellular PE would be expected to show some label because they would be able to swap 32P from solution instead of through synthesis.

 

[kryptonxenon]

If the 32P was incorporated into the membrane by direct exchange instead of through synthesis, acellular PE would be expected to show some label because they would be able to swap 32P from solution instead of through synthesis.

But how is this showing that new PE is being synthesized by bacterial cells?

 

[theonlytycrane]

So say we have acellular PE in solution with 32P and we see it doesn't take up any label. Compared to bacteria grown in solution with 32P that shows the label in their PE, we could infer that 32P is taken up as part of PE synthesis by bacteria, instead of by phosphate swaps with 32P in solution.

 

[kryptonxenon]

That makes so much more sense now. I see where I made a mistake. I didn't realize that we were actually to perform two different experiments to compare the results.