Transcription: mRNA Synthesis - Video Tutorials & Practice Problems
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concept
Transcription: mRNA Synthesis Concept 1
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Hey, everyone before we talk about transcription, it's important to go over certain key terms when it comes to this idea of MRN A synthesis. Now, here, the key terms we need to discuss are genes and pre MRN A. Now, a gene is just DNA segment containing the code for protein synthesis. Now, remember DNA is pretty large and we're not trying to copy the entire thing to make our pre MRN A or MRN A. We're just copying segments of DNA to make the protein that we need. Now, when we say pre MRN A, this is the precursor of MRN A that's processed later on into mature MRN A. Now, with this, out of the way, let's talk about transcription, transcription copies genetic information from a gene. So what we just talked about to RN A and we're gonna say here that RN A polymerase, it binds to the DNA and then it's going to unwind. So it unwinds the double helix. So if we take a look here, we have our DNA double helix notice how it is anti parallel to one another. This is five prime down to three prime with this orange strand and then three prime is here and five prime is here with this bluish strand, we're gonna save for step one R and A polymerase, which we're gonna show as this, this dark cloud part here, this grayish part is going to bind to the DNA and unwound it and it's gonna open it up, it's breaking the hydrogen bonds between the nitrogen and spaces exposing them so that our MRN A can start being created. Now, here we have this grayish RN A polymerase, we have an initiation sequence which we'll talk about. We have our template strand and we have our informational strand. So let's talk about these things. When we say our informational strand, we see that our informational strand from the first image, it goes five prime to three prime. We can see that here this orange strand five prime and then down here is three prime, our template strand which we've marked in blue runs anti parallel to it. So it would be three prime to five prime. Now, here we're going to say that our pre MRN A also called our HNRN A. So these two terms are synonymous. Your professor may use, 1 may use the other, may use them interchangeably, they mean the same thing. So this pre MRN A is synthesized on the template strand using complementary bases. And we're gonna say here, this would be our step two. And we're going to say here that transcription start from the initiation sequence So that's our start sequence. And we're gonna say transcribed, pre pre MRN A is a copy of the informational strand except that all are cells ever placed our thymine. Remember DNA uses thymine already uses Ell. So coming here, if we look here, we're gonna say that this is our pre MRN A in this magenta color, right? And it is basically starting to copy the use of complementary bases, the template strand here. And because it's doing that, it has to run uh basically anti parallel to our template strand. So this would have to be the five prime end and this would have to be the three prime end here. And we're gonna say here that since this is G, then this would have to be AC, this is R and A. So this is an A. So this has to be a U, this is an A. So this has to be A U, this is C. So this would be a G. Now here we have our free RN A nucleotides. Sometimes it happens floating around, we have what's called our termination sequence down here. And that will lead us into step three. We're gonna say that transcription stops when RN A polymerase reaches a termination sequence, our term termination sequent acts as a stop. It tells pre MRN A OK. We've copied enough of this particular segment of DNA. We no longer need to go any further. And we're gonna say here that pre MRN A is released and DNA rewinds into the double helix. So if we take a look here, the pre MRN A has been made, our DNA is rewound back to what it was originally. Again, remember it runs anti parallel to the template strand that it copied. So this would have to be the five prime and the three prime here, it hasn't been fully processed yet. So this exists as pre MRN A. Now, one more thing we said that, that the transcribed Pre MRN A is a copy of the informational strand. So if we take a look here is our informational strand that runs from five PRO down to three PRO. It's the orange strand and this one runs five prime to three prime and they're copies of each other. The difference though is that the informational strand comes from DNA. So it has thymine and the pre MRN A since it's RN A, those thymine have been changed into your cell. So if you were to look, you would see how things basically match up. So this is AC and this is AC, this is a T on the informational strand, but AR doesn't use thymine, it uses OL. So here's a Euro instead. And then here we have another team. So it'd be a U here. Here we have a G with a G. So just remember that our pre MRN A, we copied it, we made it by using the template strand and we use complementary base pair to do that. The informational strand and the pre MRN A strand are copies of each other. The informational strand is a DNA copy or version and the RN A, the pre MRN A is the RN A version. The differences are just in their bases. The informational DNA strand uses thymine, the pre MRN A strand uses your cell. So keep this in mind when we're talking about these important steps of transcription.
2
example
Transcription: mRNA Synthesis Example 1
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1m
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Video transcript
In this example, it says write the sequence of pre MRN A produced from the following DNA template strand. Now remember it has to be complementary to this. So it means we need to be anti parallel in terms of our orientation. So we have to have our three prime here and our five prime here. Remember that we're going to say since this is RNA A is linked up with U and G is linked up with C. So here we'd have CGGU AC, there's an A here. So Ugucau, so that's the way we look at this. This is the sequence of our pre MRN A. Now, if we take a look, we, we have three prime, three prime, three prime, three prime, so it should be CGG initially. So we have uh this is out and this is out. We have CGGCGG U A here. Put T remember this is RN A. So it shouldn't have finding involved. So this is out. This would be the correct answer here. We made a little bit trickier. This is the way we would see the pre MRN A but here we reversed it where we have our five prime in here. And our three prime in here, we just go from three prime to five prime. Look at how the bases match up with this DNA template strand to find the correct answer. Again, the answer here would be option D.
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Problem
Problem
Write the sequence of pre-mRNA produced from the following DNA informational strand.
5’ AATCAGTGACGT 3’
A
5’ UUAGUCACUGUA 3’
B
5’ AAUCAGUGACGU 3’
C
3’ UGCAGUGACUAA 5’
D
5’ AAUCAGTGACGU 3’
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