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Current time:0:00Total duration:10:03

Video transcript

if you were to take a look at a chromosome you would see that it's made up of this very densely packed Rayleigh known as chromatin and then if you were to further breakdown chromatin you'd see that it's made up of tremendous amount of DNA wrapped around these proteins known as histones and DNA stores our genetic information we get it from our parents and we pass it on to our children and the DNA basically determines the identity of all living organisms and just some interesting facts about DNA if you were to take the DNA that was contained in one human cell and stretch it out it would measure about two meters or approximately six feet long so that is a lot of DNA to pack into a cell that's relatively so tiny and how's that done well with the help of those proteins I mentioned histones they help to wrap DNA in a very tightly coiled and you know very dense fashion just another interesting fact if you were to take all the DNA found in one human's body and line it up together it would measure brace yourself for a very large number it would measure 100 trillion meters that is a huge number in fact something that long can go around the equator of the earth two and a half a million times so we hold in ourselves a tremendous tremendous amount of DNA but anyway let's talk about the structure of this super super important molecule that basically determines the identity of oil inning organisms so DNA is made up of three components the first is a sugar known as deoxyribose and it's called deoxyribose because there's a sugar ribose that has an oxygen right over here but deoxyribose doesn't have that oxygen so this molecules deoxyribose and the carbons in deoxyribose are labeled this carbon is labeled 1 prime primer first so that little apostrophe after the number two prime three prime this carbon is four prime and it's carbon is five prime and in case you're wondering why we need those Prime's like why can't we just leave all the carbon is carbon one two three four five so the answer that question is that we're trying to differentiate between the carbons in this molecule I will explain to in a minute what this molecule is but we're trying to differentiate between the carbons in this molecule and the carbons in the deoxyribose so for some reason the carbons in this molecule took precedence and the carbons there are labeled 1 2 3 4 5 etc and so the carbons deoxyribose are labeled 1 prime 2 prime three prime etc but anyway that takes care of deoxyribose and then the next molecule in DNA is a nitrogen base and the nitrogen base you're looking at here is actually adenine we've heard of the molecule ATP adenosine triphosphate that also has an adenine in it but anyway there are actually four different nitrogen bases that you can find in DNA so I'm going to pause for a second from what we're looking at and we're going to take a look at those four nitrogen bases this one here is adenine that's the base that we just saw a moment ago and then right next to it looking very similar is another nitrogen based guanine and you can see that adenine and guanine are both double ring structures on the left you can see they have a ring with six sides to and then attached on the right they have a ring with five sides to it and well these are all called nitrogen bases because they have a couple of nitrogen's in them and adenine and guanine are known as purines so the double ring bases are known as purines and I always have this hint to help me remember so it's really an extrinsic int because it has nothing to do the material but it always helped me so when something is pure in Glo so purines always glow that was my hint and then I would always remember that a stands for adenine and G stands for guanine so if it helps you you can use that then we have these other two bases this one here is thymine and then right next to it we have something that also looks similar to it cytosine and you can see thymine and cytosine are single ring structures they only have one ring with six sides and they are known as pyrimidines so again the purines are adenine and guanine and the pyrimidines are thymine and cytosine and the periods and pyrimidines will always pair up with each other in this fashion adenine always pairs up with thymine and guanine always pairs up with cytosine unless of course there's a problem and I want to just um let's just take a look at how these molecules pair up with each other so let's look at this diagram so the bonds that hold the nitrogen bases together are hydrogen bonds so it's hydrogen bonding that puts them together and let's just remind ourselves a hydrogen bonding takes place in molecules that have a hydrogen attached to one of three very electronegative atoms fluorine or oxygen or nitrogen let me remind you electronegative means that they like to hog electrons they pull electrons towards themselves and what's going to happen to molecules like this is that since fluorine or oxygen or nitrogen hog electrons they are going to get a slightly or maybe more than slightly negative charge which leaves the hydrogen's kind of bereft of electron density and gives them a positive charge and then the molecules will orient themselves in a way where the positive and negative sides are attracted and attached to each other so let's actually take a look at what I just explained in the molecules so let's look at finding an adenine so we have this oxygen over here which is going to be somewhat negative because it's pulling electrons away from that carbon and for in this double bond and then these hydrogens are going to be somewhat positive because the nitrogen near them is pulling electrons away and so they form this hydrogen bond right over here then we have another hydrogen bond between this positive hydrogen remember it's positive because the nitrogen here is very electronegative and ahab's all the electrons and then we have this negative nitrogen because it hogs electrons from the carbons around it so between thymine and adenine we're going to have two hydrogen bonds but if you look at cytosine and guanine there are actually three hydrogen bonds between them so we can say that cytosine and guanine are attached to each other a little bit more strongly than thymine and adenine and well what would the implications of this be so let's say we have two pairs of DNA and we're going to soon see DNA is a double-stranded molecule where the nitrogen bases pair up with each other something like this and I'm going to label this DNA set a and this one I'll label B and let's say I tell you that in a we have a very high number of A's and T's so let's say most of these are A's and T's so I'm just going to matter I'll put in a here and put it well let's make that a little bit clearer so an a and then there's going to be a T here and let's say that most of this DNA looks like that and let's say that B has a very very high number of c's and g's so here to C and here is the G and let's say that most of the DNA looks like that so B has a lot of c's and g's so which DNA do you think it's going to be harder to break and by break I mean basically break the bonds between the nitrogen bases just like that and make two separate strand and that's actually cold cold denature ization so to denature DNA means to kind of split it down the middle break the nitrogen base bonds and have two strands instead of one so again which these DNA's do you think is going to be harder to denature A or B well we just explained that between c's and g's between cytosines and wantings there are three hydrogen bonds so it would be harder to break down B because it has more seasoned g's and so one way to denature DNA is to raise the temperature that's one way to break down DNA so breaking down DNA B is going to take a higher temperature in the breaking down DNA that's just one example of why this fact would matter this fact that thymine adding up two hydrogen bonds and sizing wanna have three anyway now that we've discussed the nitrogen bases that make up DNA let's go back to actually to putting our DNA together and the various components in it so again we said the first component in DNA is deoxyribose the second thing we discussed just now were the nitrogen bases another third component in DNA is going to be a phosphate group and actually what I drew is a triphosphate it's three phosphates together and I drew it as a triphosphate because we start off with a triphosphate but eventually two of the phosphates get lopped off and we're going to be left with only one phosphate group so we're going to pause now and in part two of this topic we're going to pick up on this and see how we put together all these components to make the DNA that we have in our cells