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Current time:0:00Total duration:11:30
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Video transcript

we've already paid a lot of attention to the molecular structure of DNA in fact he right depicted in front of us we have two strands of DNA forming a double helix and we can look at the tell-tale signs that this is DNA and in particular we can look at the five carbon sugar on its backbone we see and let's actually number the carbons this is one prime two prime three prime four prime five prime we can see on the two prime carbon we don't have an oxygen attached to it we don't have a hydroxyl group attached to it and because of that we know that this is not ribose this is deoxyribose this right over here is deoxyribose and these two are also deoxyribose so that tells us that we have two strands of DNA deoxyribonucleic acid so let me write this down this this part of the chain this is derived from a deoxyribose being attached to phosphate groups and a nitrogenous base Saudi oxy deoxy deoxyribose so what would we have to do if we wanted instead of viewing this as a double as two strands of DNA in a double helix formation well how would we have to rearrange how do we have to edit the left-hand strand if instead we wanted to imagine that the left-hand strand is say messenger RNA being being generated during transcription with a single strand of DNA here on the right well to turn this into RNA or to make it look like RNA on the two prime carbon well we want to turn the the deoxyribose in to just ribose so we would want to add we would want to add a a hydroxyl group right over here so I had a hydroxyl group over there actually do that do the hydrogen's in white so add one hydroxyl group there and I want to do it on all the sugars on the left strands backbone if I want this to be a single strand of RNA and RNA tends to be single-stranded so oxygen and then a hydrogen and so this hydroxyl adding this hydroxyl group instead of just having another hydrogen just a hydrogen by itself they over there this tells us that this sugar is not no longer deoxyribose this is ribose so now we have ribose we now have ribose in our backbone which is a telltale sign that won't at least now we have the backbone of RNA ribonucleic acid versus DNA deoxyribonucleic acid now you might think we're done but we're not quite done because the nitrogenous bases on RNA are slightly different than the nitrogenous bases on DNA on DNA on DNA your nitrogenous bases are adenine guanine and adenine and guanine are the two ringed nitrogenous bases right over here this is adenine this is guanine and you also have you also have cytosine cytosine I'm gonna do these all in different colors cytosine and you're sorry cytosine and thymine I'm getting to the punchline too fast and this right over here is cytosine and this is thymine and cytosine and thymine are single ringed nitrogenous bases we call them pyrimidine adenine and guanine we call them purines this is a little bit of review in RNA in RNA you still have adenine you still have guanine you still have guanine you still have cytosine but instead of thymine you have a very close relative of thymine and that is and that is uracil so the way that this is drawn right now this nitrogenous base remember when we started this video it was double-stranded DNA this nitrogenous base right over here is thymine and it bonds it forms hydrogen bonds with adenine right over here if I want to turn into uracil I just have to get ripped I just have to get rid of this this methyl group right over here so if I just do this if I just do this and if I were to replace it with a hydrogen that is just implicitly bonded there well now I'm dealing with uracil so now I'm dealing with uracil so you see that uracil and thymine are very close molecules are very similar nitrogenous bases and that's why they can play a very similar role and it's still the case instead and and so what your cell bond what your cell pairs with it pairs still with adenine the same thing that thymine pairs with and everything else is of course still the same now an interesting question an interesting question is why uracil why not thymine or you could say withe I mean why not uracil and based on what I've read it actually turns out that uracil is a little bit more error-prone it might be able to bond with other things that when you're when you're coding it so it's a little bit less stable than thymine and so uracil uracil uracil makes the RNA molecule or actually makes the machinery of information transfer it makes it less stable that light makes it's a less stable I guess way to to transfer information and based on what I've read in in evolutionary history RNA molecules most people believe predate DNA molecules and then when you so in the early stages you had a lot of change and so your cell molecules we're just fine and there was a lot of errors and whatever else but then once you had I guess information needed to be a little bit more persistent and a little less error-prone well then thymine helped stabilize thymine help stabilize things there's also the view of what well why has your still stuck around well RNA molecules they have all of these roles in cells messenger RNA molecules are taking information from the DNA and getting it transcribed at or getting it getting it translated at the ribosome but they shouldn't hang out forever that you actually want them to be somewhat unstable so it's an interesting question to think about why do we have your cell instead of thymine or why do we have thymine instead of uracil but this is one of the tell-tale signs of that we are now dealing with an RNA molecule so now what we have on the left-hand side now all of this business actually let me do some and let me do this in a different color all of this business the strand the strand right over here we can now the way it's drawn we can now consider this an RNA molecule and if we assume that this is happening during transcription when a DNA molecule where a single-stranded DNA would want to replicate its information then this over here would be mRNA messenger messenger RNA and so what's going on here well let's think about it this one the way it's the RNA the messenger RNA way the messenger RNA the way it's oriented we have if we go we have phosphate group then we go to five prime carbon four prime three prime then phosphate group then five prime four prime three prime then phosphate group so this is oriented five prime on top three prime on the bottom while this DNA molecules are oriented the other way this is a five prime carbon this is a three prime carbon so we have phosphate three prime five prime phosphate so we have three prime is on top and five prime is on the bottom so if we wanted to think about what's happening maybe using the symbols for the nitrogenous bases we could say all right we have our M RNA molecule here and this is it's five prime end and this is it's three prime end and then the first night roller the top nitrogenous base right over here this is uracil this is uracil and then the second one over here this is this R over here this is cytosine so this is cytosine this is cytosine right over here and this is being this is being transcribed from a DNA molecule from this DNA molecule on the right hand side so this is DNA and this DNA has an anti parallel orientation it's parallel but it's kind of flipped over the the the sugars are pointed in a different direction so this is going from this is the three prime end this is the five prime end and we see that the uracil is hydrogen bonded to adenine add an e right over here so adenine and I'll draw dotted lines to show the hydrogen bonds and that the cytosine is hydrogen bonded to a guanine to guanine so this right over here that is that is guanine and I shall do the hydrogen bonds in white so you know they are actually there's multiple hydrogen bonds going on here but just to be clear this is M RNA and on the right we have DNA and this could be happening during transcription this could be happening during during I'm having trouble changing colors this could be happening during transcription now what are the types of RNA is out there we've talked about this in other videos well you have messenger RNA which is an important role in taking information from DNA and and getting it eventually translated with the help of T NR T RNAs and ribosomes and though I've just I've just measured another type of RNA and that's transfer RNA so transfer RNA T T RNA T RNA and in the video the overview video on transcription and translation we talked about how tRNA does this but it brings amino acids it has amino acids attached at one end and then it has anticodons on on the other end that that essentially pair that pair with with codon fragment or codons on the mRNA and then that's allows it to construct proteins and this actually is is this right over here is a is a visualization of a T R T RNA tRNA molecule so a lot of times when we think about when we think about DNA we think about okay Mr mRNA or RNA is an intermediary to be able to eventually translate it into proteins and that is often the case but sometimes you also just want the the RNA itself the RNA itself plays a role in the cell beyond just transmitting information and that's an example here with tRNA and you can see cut it's interesting configuration where the amino acid will attach roughly in that area up there and then you see the anticodon the anticodon right down here in the bottom right and different tRNA molecules will attach to different amino acids and they'll have different anticodons here so this is another use for RNA and then others include ribosomal RNA ribosomal RNA and they actually play a structural role in ribosomes which is which is where translation occurs and you also have things called micro RNA micro RNA which are short which are short chains of RNA which could be used to regulate that the trends the translation of other RNA molecules so RNA you know DNA gets a lot of the attention but RNA is really really really important and a lot of people believe that RNA came first in this potential that you know the first life or pseudo life ever was just self-replicating RNA molecules and that DNA eventually evolved from RNA but RNA stuck around because it's still very useful
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