A 2-kb fragment of E. coli DNA contains the complete sequence of ...

Question

A 2-kb fragment of E. coli DNA contains the complete sequence of a gene for which transcription is terminated by the rho protein. The fragment contains the complete promoter sequence as well as the terminator region of the gene. The cloned fragment is examined by band shift assay (see Research Technique 8.1). Each lane of a single electrophoresis gel contains the 2-kb cloned fragment under the following conditions:

Lane 1: 2-kb fragment alone
Lane 2: 2-kb fragment plus the core enzyme
Lane 3: 2-kb fragment plus the RNA polymerase holoenzyme
Lane 4: 2-kb fragment plus rho protein

Diagram the relative positions expected for the DNA fragments in this gel electrophoresis analysis.

Accepted Answer

Hi, everybody. Welcome back. Let's look at our next question. The molecules that need to be separated are pushed through a gel with tiny pores by an electrical field, electrical field in gel electrophoresis, which of the following statements is true regarding gel electrophoresis choice A the travel speed of molecules is directly related to their lengths. Choice B through the gel, smaller DNA molecules travel a shorter distance. Choice C larger DNA molecules travel a greater distance through the gel or choice D small DNA molecules will travel a greater distance than larger DNA molecules. So this is actually a really easy question we're being given because all of our answer choices are essentially rewording of the same thing which is, which will travel faster and farther smaller or larger molecules. And if we think about the fact that our molecules are being forced through tiny holes, it's fairly straightforward to remember that smaller molecules will travel bastard and father than larger molecules. So we can just go to our answer choices and find the one that describes this correctly since we're looking for the true statement and eliminate the incorrect ones. So choice a travel speed directly related to the links is not correct. The travel speed will be inversely related to their lengths. Since the smaller the molecule, the faster they will travel, choice b smaller molecules travel a shorter distance. Also incorrect as the smaller molecules can go further. And then to see larger molecules to a greater distance. Again, this is backwards, the larger molecules travel a smaller distance or shorter distance through the gel. And we're left with choice D which is fortunately correct, small DNA molecules will travel a greater distance than large ones. And that is our answer choice D for our true statement regarding gel electrophoresis, see you in the next video.

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