Leading and lagging strands in DNA replication | MCAT | Khan Academy
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Roles of DNA polymerase, primase, ligase, helicase and topoisomerase in DNA replication. An explanation of leading and lagging strands.
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Thanks for making this content free and accessible. This is invaluable.
is it just me or is this video extremely quiet
yeah its really low
shhhhhh
It was fine for me, but I had earbuds in.
Yeah it's quiet
its library loud my guy
Additiona info: The reason we cant add nucleotides on the 5 primer is because it lacks and OH group that DNA polymerase hook it self on. Anyway great vide.
Thanks, that's interesting
Agree
Thanks🐈
I thought there wasnt an oh group in 3' as well since it a deoxyribose so instead of OH it has just H. I thought the reason it adds on to 3 ' istead of 5' has something to do with phosphate groups lr something. I did not fully understand it but its really interesting.
@@ghffhghhdhh3600 So the 3' carbon is attached to an OH group which can attach to the phosphate group and form a phosphodiester bond which is how the DNA molecule continues to grow (5' to 3') and extend itself. The deoxyribose part comes from the fact that carbon two (not 3) is missing the the OH, and has an H instead.
OMG thank you for making this videos accessible to everyone and FREE. This is SO helpful and I can’t go through a chapter without watching all your videos that covers that particular chapter. I’m a foreign and you speak the way that anyone can understand.
Ignore the nonsense comments, your channel is awesome and I hope you are making tons of money with it.
sometimes in particular stages of life like this , you're not wasting your time, but jeopardizing your future.
all you have to do is just frickin sit and study
Thanks Rick
what do u mean?
Very good advice, Muhammad.
Really helpful, couldn't understand from the book, much better seeing the process
Such a great diagram for simplifying what my Genetic lecturer over-complicated. Thank you!
“Nuclèotides”
Made six years ago and still using this as a resource for college for an overview. I love that this is free and covers everything. Thanks so much
I’m in 9th grade and I have to learn this for biology. This is so confusing
Additionally, Single Stranded Binding proteins keep both the strands tightly away from one another so that they do Not bind again on the high complemenatrity Basis and replication could continue smoithly.
I watch all these videos at 1.5x speed and I still feel like he's talking in slow motion.
God bless you kind sir
Good to see you are still making videos. I miss you on the new calculus videos.
thank the lord for Khan Academy!
Thank god. This was really helpful. My textbook makes it sound like everything does the same thing I wish that there was a little more information on the polymerases, but it still pretty good and understandable. So thank you again.
this is a good informative video, but the way you said nucleotides got me laughing.
Best video so far!!
Thanks, it was helpful, but as you conclude you could make it more clear , by telling the viewers may be how many DNA we have formed at this point
2:40 Why are there so many things in science that are backwards
- like naming conventions 1 prime to 5 prime but physical reaction operates 5 prime to 3 prime
- OILRIG oxidation is loss of electrons, reduction is GAIN ...
- Fictitious movements of positive charge... electrons move , flow from anode to cathode
and more that i can't think of at the moment
- Fictitious forces like centrifugal force
- ... more that I cannot think of at the moment
I’m confused. Not only are primera added to the lagging strand. They are also added to the leading strand to start the process. You said that the RNA primers are replaced with DNA nucleotides and I get that. But what about the RNA primers that are on the leading strand? Won’t they be replaced as well?
thank you so much this video helped a lot
So on the bottom side we don't have ligase to accelerate the polymérisation?
What's the name of the Enzyme complex that is comprised of DNA poly, primase, ligase, helicase, and topoisomerase? I remember my bio teacher taught us they are all part of a larger enzyme but I can't remember the name!
Took my a while but I finally get the 5' to 3' stuff!
What enzyme replaces the RNA primer?
I need a LOOOOVE button Like isn't enough! THANK U SOO MUCH SIR for these great video, it cleared all the mess in my mind. It's now seeming to be a pretty easy topic😀
Thanks
the 3 prime end should have a hydroxyl group no?
WOW! that was a lot of information to ingest. but i managed to absorb it luckily. phew.
Karl Camat wow what a legend
makes more sense than class or the book. thanks for putting the time in
karen
What are the purple blumps on the backbone?
How does the cell recognize which is the true lagging and the true leading strand when everything just boils down to perspective on which one is the 3' end and which one is the 5' end?
It doesn't boil down that easily. 3' end has carbon (C) and 5' end has oxygen (O).
You are amazing!Thank you!
Can you do my exam for me?
2:05 nucléotides
why does the RNA primer not have only 1 ribonucleotide?
thank you so much for doing this. You have no idea how much relief this gives me being able to find EXACTLY what I'm needing to study this easily. Usually I'm looking all over for like an hour and I don't even get exactly what I need LOL
feel this so hard homie
Beautiful
sal was so excited to say Okazaki
Thank You So Much! You don't know how many people you are helping :)
I have a confusion about lagging strand ....that when it is forming why spaces are left in it which are filled?
I agree this wasn't explained very well in the video. There's essentially two factors at play here. Firstly, the DNA polymerase (the enzyme that builds the complimentary strand) can't start on single stranded DNA: it needs a few complimentary nucleotides that are _already attached_ to grab onto and begin replicating from. These starting nucleotides are called RNA primers and are attached to the single strand using RNA primase. Secondly, polymerase can only replicate in the 3' -> 5' direction.
In the case of the leading strand, replication is "easy". A small primer is only required at the very beginning of the strand, from which the polymerase can continuously add matching nucleotides 5' -> 3' (_i.e._ in the direction of the parent DNA molecule) all the way down the chain as its being unzipped.
Because the lagging strand runs in the wrong direction, polymerase can't just start from the beggining and work its way down like it can with the leading strand (as this would be going 3' -> 5', which it can't do). So instead what happens is small primers are peppered along the lagging strand which the polymerase grabs onto and fills in the gaps 5' -> 3' (_i.e._ away from the parent molecule) until it reaches another primer. Once it does it has to double back on itself and build up from the previous primer. Because the polymerase doesn't directly connect the phosphate sugar backbones of the DNA nucleotides to the RNA nucleotides of the primers you're left with a series of (Okazaki) fragments of double stranded DNA separated by short chunks of RNA primers. The primers are later replaced with DNA and to give a complete double strand of DNA.
I hope that makes sense lol
@@jamief415 On your first paragraph, you mention "polymerase can only replicate in the 3' -> 5' direction." but shouldn't it be '5 -> 3' direction?
@@truthseeker8200 you're right, good catch
all i can say is thank you
its good would be better if u talk about dna polymerase 1 and 3
Love the pics.
Explanation of the 5' 3' strands is unclear
Great video! Could you guys help me with this, when looking at a an bacterial GC skew, the lagging strand appears longer. Why?
Cramming for an assignment. I love this channel.
can u please try to raise the voice??!
The volume is so much low
I needed this explanation to understand the basic concepts of DNA replication and the enzyme players. Thank you so much!
Know its a long tine klater but did it gelp
Thank u so much for this video sincerely
superb !!!
I’m faced with a dilemma: If DNA expresses proteins, and specific proteins associate with DNA expression, which comes first DNA or the proteins? If it’s the former, then DNA can express itself without the need of specific proteins. It can’t be the latter because proteins result from DNA expression.
Textbook and my teacher's PowerPoint plus resources confused me. BUT THIS SAVED MY LIFE!
DNA 2.0 works differently.
does RNA primer get replaced by DNA poly 1 in both strands or just the lagging strand?
I literally learned so much from this video, this is so fascinating as well, thank you!
Really helpful!!! Much easier to understand from this than the book.
thanks for knowledge sharing
what is this program that you used??
the rna primers are not what make up the okazaki fragments, okazaki fragments are the dna that fill the gap between the primers
Video volume is EXTREMELY LOW
Great video, I always wanted to know how replication worked up close.
"I won't forget to donate"
This is an amazing video about DNA Replication. This video is really helpful for me. Thanks bro
Only video about polymerase that has made any sense to me. Thank you!
Why is the audio so low
At 6:35 things get confusing for me. I presume this is a dynamic proces, so it developes in time. The (re)wound part on the left side is only formed later then the unwinding at the right-handed side. The video suggests round 6:35 that things develop from the left side, but that isn''t there yet, so the video goes with and against time at the same time.
I got confused here to. he said dna polymerase III builds from the 5 prime to 3 prime direction. in the diagram, it looks like the opposite....
Just too complicated for a simple diagram. This might help ruclips.net/video/v8gH404a3Gg/видео.html
This one is very quiet
this is a life saver, thank you so much!
Sever Audio issues
Thank you so much for this awesome video!
it should also be noted that while it seems implied that the leading strand finishes this faster both DNA pol 3's on each strand interact with each other and synthesize simultaneously so replication of both strands finishes at the same time.
It was excellent
Why do Okazaki fragments have to be in fragments? How come once the polymerase is bound to the RNA primer, DNA polymerase can't just continually add nucleotides in the 5' to 3' direction?
Adrian Choppa yeah i don't understand this too. As the DNA strands can be separated in both ways, why can't the lagging strand be replicated in the opposite direction continuously...
This is my understanding of the process:
It has to do with how the DNA is unzipped. All of this happens simultaneously, so as it's unzipped, it's also being replicated. Since it doesn't wait for it to fully unzip, it has to do it in segments on the lagging strand constantly trying to keep up with the DNA primase and helicase. So, DNA polymerase will add in the 5' to 3' direction for 10-15 nucleotides worth of an Okazaki fragment as the DNA primase and helicase keep moving in the 3' to 5' direction (for the lagging strand anyway), then the DNA polymerase will quickly "run" past the fragment it just created and the one it's about to create so it doesn't fall too far behind the DNA primase and helicase and make another fragment in the 5' to 3' direction, and on and on it goes. All the while, DNA ligase is linking up all these fragments.
DNA Polymerase III can only add nucleotides in the 5' to 3' direction. Because DNA is antiparallel, there is one strand that goes 5' to 3' and the opposite strand going from 3' to 5'. When you use helicase, the hydrogen bonds between the nitrogenous bases are broken and the two strands are pulled apart in order to start replication. You still have one strand going 5' to 3' and another strand going in the opposite direction - 3' to 5'. The main reason DNA Polymerase III can't go 3' to 5' is because it just isn't oriented to do so. It has the wrong shape, if you will. So you're going to have one strand that's relatively seamless and continuous (leading strand), and you'll have your antiparallel strand with Okazaki fragments that lags behind (lagging strand). I hope this helped!
Because you're not unzipping them in separate ways. Think about it this way: if you first unzipped the entire DNA molecule, you could have DNA polymerase launch off of a primer and easily code. The problem is, it would take forever to just wait for the entire thing to unzip, and you can see in the diagram in this video that the lagging strand and leading strand are being replicated at the same time. Imagine brooming, but you don't start at the end of the room. If you have a tiled floor, you would start at the three closest tiles and broom toward you, and then go down six and broom those way back to the pile of dust you're planning on making. That's what's going on in the lagging strand. But once you have these fragments sitting around, you have to attach them together so that they connect. That's what DNA ligase does. I hope that makes it kinda easier.
from my understanding, at the lagging strand, as the helicase moves (from 5' to 3' direction of parental strand) it leaves single stranded region that will be filled with a primer. Then dna polymerase comes and fill in gaps with free nucleotides going to the opposite direction of helicase (3' to 5'). but then helicase keeps on moving from 5' to 3' again and creates new single strand region AGAIN and the rna and dna nucleotides attach to the single strand AGAIn and it repeats. that's why it is fragmented, bc there many primers formed. i guess you forgot the fact that helicase, it keeps on moving, creating new single stranded region everytime, and the fact that rna primase also moves in the direction of helicase. hope you understand.
is the dna opening up in the right direction
I love you
lost after5:00
So does DNA-Ligase replace all of the Okazaki fragments, or just the uracil nucleotides. I ask this because DNA and RNA share some 3 out of 4 nucleotides.
nickonde DNA ligase links the Okazaki fragments
Thank you so much for making great content that is also free
Great Video!
How is this guy so familiar with everything
🤮🤢🤕
What software do you use?
Your voice is unable to hear
thats really amazing for me as student
The graphics tho
Thank you! You are awesome
best explanation online! much more detailed and clear things up so much better, now i get it.
what about the telomerase
thanks khan academy! you've always been helpful ❤
david
Yay! No longer confused!
Thank You so much.
question:
Can we say that leading strand has just only one okazaki fragment?
Orçun Sami No..can u say that 2 DNA strands are actually 2 fragments??leading is continuous but lagging moves in fragments joined latter by ligase
Thank you so much
🔝🔝🔝🔝🔝🔝🔝
Thanks 💙
Would 3’ end not have OH..?
Yes it does
What about the trombone loops?
Extremely poor audio😣