hi everyone and welcome back to higher biology we're continuing with you know one DNA in the genome and good to move on to Keeler tube which is replication of DNA so last time we will take either one we looked at the structure of DNA really the bonds hold the DNA double helix together and we also looked at the three prime and five prime ends of DNA and that could be quite useful in this part now so to continue on with the replication of DNA you might never from national find that in mitosis there's a terminus or mitosis that just says that DNA is duplicated or DNA is replicated and then we go on to producing two new daughter cells what were granted higher is a bit more detail on how DNA actually replicates and ions Hara double helix DNA makes an exact copy of itself so let's look at less essential happens in DNA replication through three stages you start off the original strand of DNA were then going to split the snow weak hydrogen bonds winter break between them the new bases of DNA are going to be added to each strand to make another strand of DNA to go into that more detail here we're talking about these hydrogen bonds that hold the bases together the complementary base pairs in a DNA double helix during the process within the replication the DNA unwinds and those weak hydrogen bonds break between them so that's the light was the two strands today one zip into two template strands and this is something we call wine shade replication fork basically where DNA replication is about to take place there's too many times wouldn't be looking at during the process of DNA replication you might remember from Keira one will litter the front at the three prime end of DNA and the 5 prime end of DNA and you may remember that DNA could only be added to the 3 prime end so if you look at this diagram in the middle you can see you have a 3 prime end and you forgot this one strand of DNA because the weak hydrogen bonds have been broken between them this strand we weren't called the leading strand and it's the leading strand because the comprehension tinea nucleotides can be added continuously to this and to make a new strand of DNA it goes up it just continuously almost like a zipper going up a jacket the other strands of DNA doh the 5-prime end is going to pull the lagging strand so we think wagging means it's curve has fallen behind a little bit it's not as simple as the 3-prime leading strand process this is not a continuous zip what happens here is the complementary DNA nucleotides make fragments of DNA so individual fragments are joined together in the five prime end in order to make a new strand but when smoothy toughest in available so when we look at the formation of this three prime leading strand first of all we're going to have couple new ones here first of all one is primers so primers are sure complementary sequences of nucleotides that are required at the start of a new DNA strand so never DNA replication starting to take place you have the three prime end of the DNA strand and the primer is added to it to begin the process a subset here looks can only bind to the three prime end to begin this new process of making the complementary strand when I taught that complex transfer clear member that you have complementary base pairs so for example C matches with G e matches of T try to remember those because I can come up as well so these complementary nucleotides that match the DNA base pairs they get added through an enzyme this enzyme is called DNA polymerase so this has the complementary proteins onto this new strand and there starts a complementary strand from the new 5 prime to 3 and plane end so you have the original DNA strand at the 3 prime end the player comes cross starts panting the complimentary for tights and that zips all the way up to create this new strand as I said the lagging strand is a bit more complicated you need several primers at this replication fork well the DNA unwinds and again DNA polymerase still does the same job ads free complimentary imitates they're in the area they get added to the Strand but it's added and fragments so it's not the nice continued line it's at the three prime end adding in fragments and they are joined together other enzyme this enzyme is called why gates and it works a bit like a belly glue so you have these different fragments of comprehension nucleotides they're all joined together as a discontinuous strands not just one long strand it's working all the way up these fragments are joined together by like ears to make an RNA strand I don't know part to be aware of as this doesn't happen just at the end of one part of DNA apart all the way up this is something that's continuously happening during the Indian replication to make sure the whole pumas one was requisite quickly and efficiently there's lots of different replication for screwing on through a DNA strand so every single DNA molecule is composed of one original strand I want the new strands but there are several replication for replication works which are working at the same time 3 after this site here just gives you an overview of the requirements and the function of everything from DNA replication in case you're asked the exam what is required for DNA replication to take place so obviously you have your original DNA template and we're going to be having some free DNA nucleotides to make the new complementary strands we've already came across primers so you need your primers in order to start the process of DNA replication I've got a couple of enzymes that have been added so DNA polymerase is the enzyme that adds the free equal tides to make a new complex strand over the fragments and making new component to strands and don't know it's lagging strands you have an old enzyme ligase which is like glue that I've spoke about that joins the DNA fragments together finally something you need is ATP because Fred the process of DNA replication energy is required for as well so try remember that ATP is also required for DNA replication the last part of this key area is called the polymerase chain reaction or PCR and this is a fate for the same thing as DNA replication but it's been done in a laboratory environment so PCR is a technique used to create many copies of a fraction of DNA in a lab setting we also call this amplification of DNA meaning that you make a large quantity DNA will look at uses of s shortly but if you imagine that you were using a strand of DNA for forensics for example or some sort of medical testing if you only have one that you test on it then it's being used up what you want to do in a lab setting is amplify or make a large amount of DNA so used to lots of different tests but this is what PCR is all about so to start off with again in the form of DNA replication original DNA template strand is required so in this case has to be the DNA that you bought top five that you want to have lots of different copies off in the first type of PCR reuse machine call of thermal cycler what happens is DNA sample you have as he T to t 92 and 90 degrees Celsius what this does is this breaks those weak hydrogen bonds that connect the complementary base pairs from the DNA double helix so these DNA strands are now under broken apart in the second part of polymerase chain reaction the DNA sample is then cooled so you don't want as hot anymore to break those bonds the two strands are then cooled to 50 to 65 degrees Celsius and this allows these primers to bond to the separated DNA strands so as we saw from DNA replication previously these primers for your short short strands of DNA they attach come across to the three prime end of the DNA strands under step 3 the DNA sample is heated again so it goes up to 70 to 80 degrees Celsius to allow DNA polymerase to bring these complementary nucleotides to the three prime ends just like we've seen again in DNA replication the one that it's important to note here do is test DNA plenary is enzyme is heat tolerant okay it's quite hot the stage you want to have DNA polymerase that could handle that temperature so again the DNA plenaries theus nucleotides and as confirmation rotates the three prime end of the original strands to make up new strands this diagram here shows you the this round of PCR again as well because the top of the temperature quite a lot I could be asked that and they so again if you step one here you can see the heating has taken place temperatures went up those hydrogen bonds have broken in step two there's we have a problem the cooling taking place and that's when the primers are added in step three the temperature starts to increase again so reheating and that heat-resistant DNA polymerase has been added these new strands are being produced a failure we'll look at step four we're basically the first strand of DNA replication has ended so we've now got a new replication of DNA taking place so at the end of this first like who you now have two identical strands or molecules of DNA from the one that you had then you might be wanting more than those though so the cycle is going to repeat until you have the number of DNA molecules that you want so for example if you look at the table here you can continue to double the copies of DNA you have with every cycle of PCR and I would have as many as you want as I said there we're on the machine that you used carry this process is called a thermal cycler essentially it was a machine it was recycles of different temperatures for a PCR this was partly carousel repeated cycles of PCR and eventually you can create millions of copies of a certain piece of DNA that you want within a few hours so to create a useful in a lab setting one thing you should be aware of as well is what you would actually want to use this for so I spoke about a little bit earlier on so for example for forensics you can have small quantities of DNA from something such a crime scene you can amplify this so you can use the DNA or have lots copies of DNA to determine who is there some oil you can use the DNA for paternity testing to find out who's the parent or if you're related to it or individual and finally we're using PCR quite a lot food diagnosis or through medical tests now we could have embryonic DNA samples you could check for example genetic disorders before birth the last part we look at here is the requirements of PCR so it's quite somewhere to the requirements of DNA replication for causes and life requirement there's all things that you need to add so again you have your original DNA template strand for the cocaine to take place you need to have primers that are frightened of DNA and began the process you need your supply of nucleotides cells you have four types so you create four bases of DNA that are required one of things we do add to PCR is a pH buffer and what that does is it make sure that optimum pH is always there the process of PCR and as you spoke before you that heat tolerant DNA polymerase so enzyme is going to used to synthesize the new strand of DNA and the whole process takes place within a thermal cycler or a thermal cycler machine so that's all we need to know for replication of DNA in the two forms you've got your conservation of DNA for your sub your polymerase chain reaction and the uses of it so that continues off the back of the structure of DNA and we use this to move forward on to key area 3 thanks so much for listening folks I'll get the new one as soon as possible thank you