For the lac genotypes shown in the following table, predict whether the structural genes (Z) are constitutive, permanently repressed, or inducible in the presence of lactose. Genotype Constitutive Repressed Inducible I⁺O⁺Z⁺ x I⁻O⁺Z⁺ I⁻OᶜZ⁺ I⁻OᶜZ⁺/F'O⁺ I⁺OᶜZ⁺/F'O⁺ IˢO⁺Z⁺ IˢO⁺Z⁺/F'I⁺

Video transcript

Hi everyone welcome back. Let's look at our next problem. It says two vital regulators control the lack opera on turning it on or off while the metabolite activator protein. Cap senses blank. The lac repressor. One of the regulators senses blank. Let's recall the purpose of our lack. Opera controls the expression of the genes for the enzymes needed to digest lactose for bacteria to digest lactose. And there's kind of two things you want being part of this regulation of course lactose should be present. Doesn't make any sense to make those enzymes if there's no lactose and glucose should be absent. So lactose present because glucose is a better source of energy. You don't want the bacteria digesting lactose if there is glucose there. So we're going to go ahead and eliminate our two answer choices that have lactose in them. So C and D. Will cross out because it's mainly lack the presence of lactose and glucose. That is of importance here. So the Kuttab light activator protein is we can recall is what senses glucose oops the glucose levels when they fall low, the cell produces the molecule C A. M. P. So when glucose is absent, C A M. P. Is produced. C A. M. P binds to cap cap then binds to the cap binding site and this enhances the transcription of those genes. It helps RNA polymerase to bind more tightly and that turns up the gene expression higher. So cap senses glucose. So we're going to know that we know that it's choice A. Because Choice B. Has lactose first and cap is not used to sense lactose so we can eliminate Choice B. We know that Choice A is our correct answer. But let's just walk through real briefly. We see that um we know that our lac repressor senses lactose. Uh When lactose is present, some of it is I summarized, a low lactose lactose binds to the lac repressor, which releases it and while it's bound to the operator it's finding site. It prevents the transcription of those genes because it blocks RNA polymerase binding. But when lactose is present, it's a low lactose form binds to the lac repressor releases it from its operator site, allowing RNA polymerase to come in and transcription to take place. So again the cap protein senses choice A glucose and the lac repressor senses lactose. See you in the next video.