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

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. 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
Explain the relative positions of bands in lanes 1 and 4.

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

Explain the relative positions of bands in lanes 1 and 4.

Accepted Answer

Welcome back. Everybody. Look at our next question. Which of the following statements about band shift assay results is true. Choice. A, the electrolytic mobility of control DNA is slower than that of experimental DNA. Choice B, the electro mobility of experimental DNA is slower than that of control DNA. Choice C, the electro mobility of both the control and experimental DNA is the same and choice D the experimental DNA possesses an electrophrenic mobility but the control DNA does not. So for this question, let's think about what a band shift essay is. And that's when you have an experiment where your control DNA is just what's called. And I'm putting quotations naked DNA. So a sample of DNA with nothing else mixed in. Then your experimental DNA is a sample of DNA plus proteins that you think might bind to that DNA often I'll put and print these transcription factors. Now, the key is when the proteins bind to the DNA that makes a bigger molecule. So proteins plus sine DNA equals a larger molecule. And we can recall that when we run molecules on a gel, a larger molecule will move more slowly through the gel. The molecules have to be forced through the pores in the gel. So a larger molecule won't move as quickly. So with that in mind, let's look at our answer choices. We know that our plane or controlled DNA will be smaller and our DNA with proteins bound to it or experimental DNA will be larger. So in that case, the larger DNA will be slower. So choice B should be correct. The electro mobility of experimental DNA is slower than that of control DNA. Since that DNA plus sign proteins is larger, let's just look briefly at our other answer. Choices. Choice A says the control DNA is slower amount of experimental DNA. But we, as we just discussed, that's not correct. The control DNA is just plain DNA, those molecules are smaller, they move faster. Choi says the mobility is the same of both control and experimental. Well, that's not true. And indeed, that would wreck the whole purpose of our essay. And then finally, choice D the experimental DNA possesses electro mobility but the control does not. Well, this is not true. All DNA will move through a gel as it's negatively charged. So again, which statement about bands shift essay results is true. Choice B the electro mobility of experimental DNA is slower than that of control DNA. See you in the next video.

Key Concepts

Transcription and RNA Polymerase

Rho-Dependent Termination

Electrophoresis and Band Shift Assay

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