Jesus, finally someone explained this properly. this is the 10th clip I watched and now can understand this end replication problem. thank you for sharing.
just reading about histone codes and the histone sequence in human. is very complex for me. that is about heterochromatin, euchromatin and histone tails, x chromosome deactivation, methylation and acetylation of histones affecting epigenetic and genetics. I wish you was here to read this with me.
Woow .. interesting topics ... I will try to speak about them in my coming videos maybe next week .. so stay arround ;) .. this week I am working on PCR and rt-PCR the video will be up tomorrow I think ...
There's quite a few things missing in this video. Especially, since we're talking about the end replication problem, there is a need to mention that the lagging strand and its template strand never really fully get replicated, there's always a part of the extended DNA that doesn't get replicated. The telomere essentially has both double stranded and single stranded regions, the single stranded region of the telomere loops around and forms a knot in the telomeric region which stabilizes the ends of DNA.
If replication of large eukaryotic chromosome is initiated at multiple origins of replication ( replication bubbles) the end replication problem should probably happen on each replication bubble. Why it only happens at telomere?
@@hyderali692 I think it's because each replication fork eventually runs into a replication fork running in the opposite direction (they meet). So all of the DNA is replicated there.
@@haykojan6590 if you don't care about learning material as close as accurate, as possible, I am sorry. If I had the academia and time to create a video, I would. However, I am no one to do so, just like you. Just stating an opinion based on what I have learned from professionals. If you don't like my comment and are offended, then maybe science is not for you. There is a lot of criticism and people, just like myself make and learn from mistakes! That is the beautiful thing about science. God bless you and best of luck in your path to success.
Like other students, I finally found it explained correctly and logically after a lot of unuseful videos. The most convincing explanation of telomeres. Thanks alot.
thank you for this explanation, I've been trying to get my head around this for hours but every other explanation on the internet is awful, so thank you for saving me!
Thank u so much. This is the best video on RU-vid explaining the end replication problem and its solution by telomerase enzyme. Really very helpful video for students. God bless u !!
Thank you for the nice explanation. I am wondering why only lagging strands are facing telomere shortenings, why not the leading strands as they also had primer at their starting points and there is no way to replace it with DNA? Could you please explain?
This is the best explanation I have ever seen on this topic.Finally I have clear my doubts regarding this topic.Thank you so much for clearing my doubts . I wish you will keep it up always.
How can the first daughter dna thread be built from 5 to 3 in the 3 to 5 sequence when there is no OH mould for the first nucleotide to be built on ? Or the forst nucleotide doesn't need an OH ?
Hi! Thank you so much for uploading this! I am just very confused about one thing - why would this not happened on BOTH the lagging AND leading strand? In both cases there is no OH for the new nucleotide to be added to when filling in primers at the end. Afterall wasnt the leading strand also started with a primer as well? Why can that one get filled in easily but the one at the end of the lagging strand cause such a problem? Thank you so much for you help in advance!
In the leading strand there is only one RNA primer at the beginning of the daughter strand. At the end of DNA replication this RNA primer is removed nucleotide by nucleotide and each removed nucleotide is replaced by a DNA nucleotide using an enzyme called DNA polymerase (I), this sequence of DNA which replaces the removed RNA primer is then linked with the rest of the daughter strand using the enzyme Ligase. Now you may ask why this does not happen in the lagging strand? the problem is that the mechanism of replication is totally different in the lagging strand, because there are many RNA primers, each one of them has a different sequence, these RNA primers are removed all at once, then the gaps are filled normally with DNA polymerase starting from each OKAZAKI fragment, but this enzyme usually forgets to replace the last RNA primer because of the missing of -OH, so this enzyme does not sense the absence of the last strand which is rather sensed by the enzyme telomerase which in turn fixes this issue. I hope I answered your question.
Thanku so very much ma'am ...I have so much confusion regarding this topic...Bt by the help of your video my every confusion gets clear.again TSM...ma'am
I would like to ask a question. If as you said RNA primer at the end can not replaced because of lack of free OH group, then how RNA primer in the leading strand is replaced? Because the begining part is 5' which is continuously written by DNA polymerase and lack OH group.
in my book it says that at the end of the lagging strand you can't even attach a RNA primer because helicase goes away and without it, RNA-primase cannot attach a primer.
OK, so you forgot to mention that there is a rna primer at the beginning of the leading strand, so how is that rna primer replaced cuz if the exonuclease removes it there isn't a 3' for the dna polymerase to attach to?
this is exactly the same question that has been haunting me for hours! I've watched a lot of videos about the end replication problem but they all forgot to mention that there is a primer at the begginng of the leading strand too! Someone please help me I can't find the explanation for this anywhere :(
because leading strand's primer is somewhere within the DNA, it will eventually be filled by dna coming from the leading strand of the previous replication fork.
That is done in prokaryotes by DNA Polymerase I. It has a unique 5' to 3' exonuclease activity that can replace the RNA primer and then replace it with DNA. In Eukaryotes the removal is done by RNase H and Flap Endonucleases
There is one thing that I don't understand- we also have a primer on the 5' end of the leading strand and when we take it off we are left without an OH group (right?). How can it be that the end replication problem doesn't happen in the leading strand as well?
at 10:03, when the parent strand is elongated by the Telomerase and the rna primer comes and the daughter strand is completed, what happens to the part where the rna primer and parent strand disappears in the video?
Hi, I'm not sure if anybody has pointed this out or it may be just be but @5:12 , isn't the 5'-3' meant to be the leading strand whilst the 3'-5' is the lagging strand?
