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Video transcript

as long as human beings have been around I could imagine that they've noticed that offspring intend to have traits in common with the parent for example someone might have told you hey you walk kind of like your dad or your smile is kind of like your mom or or your your eyes are like whoa you're one of your uncle's or your grandparents and so there's always been this notion of inherited traits but it wasn't until the 1800s that started to be studied in a more scientific way with Gregor Mendel Mendel the the father of genetics but even then even Mendel who was starting to understand the the mechanisms of or he was trying to understand how inheritance happens and you even could start to breed certain types of things even he didn't know exactly what was a molecular basis for inheritance and the answer to that question wasn't figured out until fairly recent times until the mid 20th century not until the structure of DNA was established by Watson and Crick and their work was based on the work of many others especially folks like rosalind Franklin who who essentially provided the bulk of the data for Watson and Crick's work Maurice Wilkins and many many many other folks but is really the the structure of DNA that made people say hey that looks like the moat that looks like the molecule that that's storing the information just to be clear DNA wasn't discovered in 1953 DNA did was discovered in the mid-1800s it was this kind of this this molecule that was inside of nuclei of cells and for some time people said well maybe this could be the molecular basis of inheritance you know you can imagine what you would need to be a molecular basis of inheritance it would have to be a molecule or a series of molecules that could contain information that could be replicated that could be expressed in some way but it wasn't until 1953 we're in this double helix structure of DNA was establish that people said hey this looks like this looks like our molecule so first let's just talk about the structure here and then actually we'll talk about where this named DNA deoxyribonucleic acid comes from and then we'll talk a little bit about why why this structure lends itself well to thing that stores information that can replicate its information and that could express its information we might go in depth on the expression of information in future videos so this structure right over here and this is a visual depiction of a DNA molecule you could view this as kind of a twisted ladder it has these two I guess you could say sides of the ladder they're twisted that is one side right over there and then it is another side there is another side right over here and in between in between those two sides are connecting those two sides of that twisted ladder you have these rungs and these rungs are actually where the information the genetic information is I guess you could say stored in some way because these rungs it's a sequence of different bases and when I say bases at the United Way this has acid why are you saying bases right over here well the word deoxyribonucleic acid comes from the fact that this backbone is made up of a combination of sugar and phosphate and the sugar that makes up the backbone is deoxyribose so that's essentially the D and DNA and then the phosphate group is acidic and that's so where you get the acid part of it a nucleic is say this was found in nuclei of cells it is nucleic acid deoxyribonucleic acid but it's not it also it is it has actually mildly acidic all in total but for every acid it actually also has a base and that base for those bases form the rung of the ladders and actually each rung is a pair of bases and as I said that's where the information is actually stored or what am I talking about well let me talk about the four different bases that make up the rungs of a DNA molecule so you have adenine a adenine and so for example this part right over here this this this section of that rung might be adenine maybe this right over here is adenine this right over here remember each of these rungs are made up by its a pair of bases and that might be adenine maybe this is adenine and now I can stop there automail do maybe that's adenine right over there and adenine always pairs with the base thymine so let me write that down so I adenine pairs with thymine thymine so if that's an adenine there then this is going to be a thymine if this is an adenine then this is going to be a thymine or if I drew the thymine first while say ok it's going to pair with the adenine so this is going to be a thymine right over here this is going to be a thymine if I were to draw this this would be a thymine right over here now the other two bases you have cytosine which pairs with guanine or guanine that pairs with cytosine so guanine and we're not going to go into the the the molecular structure of these bases just yet although these are good we're good names to know because they show up a lot and they really form kind of the code your genetic code guanine guanine pairs with cytosine guanine and cytosine cytosine so actually if this is let's say there's some site is in there let's say cytosine right over here maybe this is a cytosine maybe this is cytosine maybe this is cytosine this is cytosine and maybe this is cytosine then it always pairs with the guanine if we're talking to so let's see this is guanine then and this will be guanine this is guanine this is guanine I actually didn't draw a stuff here but this is guanine I didn't say what these could be but these would these would be made of pairs of they could be adenine thymine pairs and it could be adenine on either side or the thymine on either side and they could be made of guanine cytosine pairs with a guanine or the cytosine is on the other side actually just to make it a little bit more complete let me just let me just color in on the rungs here as best as I can so that's those are guanine so they're going to pair with cytosine pair with cytosine pair with cytosine and when you strong this way you might start to see how this is essentially a code the order of which the bases are R hat I guess the the order in which that we have these the seek or the sequence of these bases essentially encode the information that make you you and you could debate well how much of it is nature versus nurture and when people say nature you know it's literally genetic and that's that's an ongoing bate an ongoing debate but it does code for things like your hair color you know when you see that your smile is similar to your your parents it is because that information to a large degree is encoded genetically it can affect it affects a lot of what makes you you and actually not even just within a species but also cross across species what humans have more genetic material in common with other humans than they do with say a plant but all living creatures as we know them have genetic information this is the basis by which they are passing down their actual traits now you might be saying well how much genetic information does a human being have and the number will will either disappoint you or you might find it mine mind-boggling the human genome the human genome and every species has a different number of base pairs to large degree correlated with how complex they are although not always but the human genome the human genome has six million set aside not six million six billion six million would be disappointing even billion might be disappointing six billion base pairs six billion six billion base pairs and when you have your full complement of chromosomes and this is in most of your the cells in your body and outside of your your your your sex cells or your the sperm or the egg cells this is going to be spread over 46 46 chromosomes 46 chromosomes I guess you'd say 23 pair of chromosomes so if you divide 6 billion by 46 you get a little over on average 100 million I think it's a hundred and something million base pairs per chromosome and some chromosomes are longer actually there's some longest are over 200 million and some might be shorter that's just on average now this number might to some of you might be exciting you like I did I thought I was a simple creature I didn't know I was I was this complex 6 billion that's a lot of base pairs that feels like a lot of information for others of you it might not feel so great you might say hey wait I could I could store this much information on a modern thumb drive or on a hard disk I thought I was I thought I was I was more more unique that and of course we all are special and unique but you might say only 6 billion base pairs I thought was you know I was infinitely complex and whatever else and there's some arguments for that and along some some other directions but this is on the approximate length I guess you could say the approximate size of the actual human genome and when we talk about chromosomes it'll talk about chromosomes much much more death depth imagine taking this this zoomed in thing that you have right over here and you know over here I don't know how many we have like 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 we have about 20 base pairs depicted here imagine if you had about 200 million of these base pairs and then you were to take this thing and you were to kind of coil it up into that thing is a a is a chromosome is a chromosome and you're saying wait I have that much information in most of the cells of my body this thing must be incredibly compact packed and if you said that I would say yes you are correct this this the radius the radius of the DNA molecule is on the order of one nanometer one nanometer which is a billionth of a meter so you can start to assess kind of the scale of this thing this is a very dense way to actually store information but just to have an appreciation of and you might have seen it when I was colouring in on on why this structure lends itself to being able to replicate the information or even to be able to translate or Express the information let's think about if you were to take this ladder and you were to just kind of split all the base pairs so you just have one half of them so you essentially have half of the ladder and so if you only have half of the ladder you're able to construct the other half of the ladder let's let's take an example let's say and I'll just use the first letter to abbreviate for each of these bases so let's say you have some so let's say this is one of the this is the sugar phosphate backbone right over here so this could be one of the one of the sides let's say there's some adenine actually we do them in the right color so you got some adenine adenine maybe some adenine right over here maybe there's an adenine there maybe you have some thymine thymine maybe thymine right over here you have some you have some guanine guanine guanine and then let's say you have some cytosine and you have some cytosine so if with just half of the of this of this ladder I guess you could say you're able to construct to the other half and that's actually how DNA replicates this ladder splits and then each of those two halves of that ladder are able to construct versions of the other half or are versions of the other half were able to be constructed on top of that on top of that half so how does that happen well it's based on how these bases pair adenine always pairs with thymine if we're talking about DNA so if you have an a there you're gonna have a T on this end T on this end T's right all over here T right over there if you have a T on that end you're going to have an a right over there a a if you have a G a guanine on this side you're going to have a cytosine on the other side cytosine cytosine cytosine and if you have a cytosine you're going to have a guanine on the other side and so hopefully that gives you an appreciation of how DNA can replicate itself and as we'll see also how this information can be translated to other forms of either related molecules but eventually to proteins and just to kind of round out this video to get a real visual sense what the DNA molecule looks like or it gets a different visual depiction from this I found this this animated that's animated jiff that you know if you haven't fully digested what a double helix looks like this is it and you see here you see your sugar phosphate bases here you see kind of the sugars and phosphate the sugars and the phosphates alternating along this backbone and then the rungs of the ladder are these base pairs so this is one of the bases that's the corresponding that's its corresponding I guess you could say partner and you could see that along all the way up and down this molecule very exciting