Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation. No initiation occurs.

Video transcript

Welcome back, everyone. Here's our next question. It says, which of the following enzymes directs the synthesis of a short RN a segment called a primer that is complementary to DNA. Let's recall that when DNA is being replicated, the DNA polymerase that actually synthesizes the new strand can't just um bind and start um adding on bases spontaneously to the unwound DNA strand. It needs this short RN a segment that's complementary to that DNA strand that acts as a primer. Um And then it recognizes the primer binds on and starts the DNA polymerase recognizes the primer and starts adding new nucleotides to start creating the new replicated strand. So which of the enzymes directs the synthesis of this primer? Well, we have a nice clue in our name. Our answer is choice C primate. So that name primate can help us remember that. Um Let's just look over our other answer choices to understand why they're incorrect. Choice. A is helicase. Well, that of course, is the enzyme that unwinds that double strand of DNA to begin replication. So that's why that's not our answer choice. Cross that off. Uh topo is, is not our answer choice um to, is role is to re relieve the super coiling that's caused as you unwind that DNA strand super really. So as you pull the two strands apart, um the the double strand behind it sort of begins to super coil in upon itself. So you have to, to is to relieve that super coiling um by cutting the strand and relig it, but it doesn't synthesize RN I primers. So it's not our answer. And finally, um is what uh is not our answer because it's what joins together the Okazaki fragments, those fragments of the lagging strand synthesis that need to be joined together to create one continuous, newly replicated DNA strand. But again, not our answer here. So which of the following enzymes directs the synthesis of a short RN a segment called a primer complimentary DNA choice C primate. See you in the next video.