Northern blot analysis is performed on cellular mRNA iso...

Question

Northern blot analysis is performed on cellular mRNA isolated from E. coli. The probe used in the northern blot analysis hybridizes to a portion of the lacY sequence. Below is an example of the gel from northern blot analysis for a wild-type lac⁺ bacterial strain. In this gel, lane 1 is from bacteria grown in a medium containing only glucose (minimal medium). Lane 2 is from bacteria in a medium containing only lactose. Following the style of this diagram, draw the gel appearance for northern blots of the bacteria listed below. In each case, lane 1 is for mRNA isolated after growth in a glucose-containing (minimal) medium, and lane 2 is for mRNA isolated after growth in a lactose-only medium.

lac⁺ bacteria with the genotype I⁺ P⁺ Oᶜ Z⁺ Y⁺

Accepted Answer

Welcome everyone. Let's look at the next question. Suppose you conduct a northern blood analysis using a probe specific to the lack Y gene of lac bacteria lack negative bacteria. Excuse me, with nonfunctional promoter and operator regions. What will you expect in the appearance of gel electrophoresis? When you run an M R N A isolated after growth in a lactose, only medium choice A, a strong visible band will appear at the bottom of the gel. Choice B different colors of bands will appear on the gel. Do I see weak or absent band near the bottom of the gel or choice D? None of the options is correct. Well, even before we start to analyze this, we can eliminate one choice which is choice B different colors of bands. Uh we don't have different color bands on a northern block. So not part of the northern blot, you see different color um read out on a sequencing gel. Although they are not on the gel itself, you see that on the print out, but you don't see different color bands on a northern block. So choice B is not our answer. So let's think about what's happening here, the northern block. Of course, we're looking for a complimentary sequence with our probe. So we're looking for lack Y M R N A that's been expressed. So we're looking for LA Y M R N A expression. Our bacteria has no promoter or operator region and our bacteria has been grown in lactose only medium. So lactose is present glucose is absent. So those conditions usually result in high expression of the black jeans. You have your oppressor being removed due to the presence of lactose. And with glucose absent, you have the C A MP cap binding to the cap binding site which turns up transcription by enhancing the binding of the promoter. However, we have no functional promoter and therefore no lack gene expression because the promoter of course is where R N A prelimerase spins to transcribe the genes. So with no lax gene expression, we're going to see choice C a weak or absent band near the bottom of the gel. So choice a, a strong band will not be our correct answer because we're not going to see the expression of that gene. And since we have found a correct answer. Choice, D, none of the option is correct is also not our answer. So again, in this situation where non with nonfunctional promoter and operator regions, we will not see expression of the lack Y gene and therefore, will not see any sort of strong band when we run with a lack Y probe. So choice c weak or absent band near the bottom of the gel. See you in the next video.

Key Concepts

Northern Blotting

Lac Operon

Gene Expression Regulation

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