mparkes17
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How can you tell the leading and lagging strand apart?
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TSR_Ollie
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Hi - sorry you haven't had a response to this yet. I'm just going to bump the thread in the hope that someone sees this and can help

Why do I do this?

The Universities forums get a lot of questions that are unanswered. This is often because the OP's thread got missed - bumping threads gives them another lease of life and frequently results in someone seeing it and being able to respond

If you would like to help with unanswered questions check out the first part of the list here and don't forget the second part of the list here.

Or if you have questions, get in touch with Puddles the Monkey.
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anosmianAcrimony
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The leading strand is synthesised in one long piece, whereas the lagging strand in synthesised in a bunch of smaller pieces called Okazaki fragments.

Name:  DNA-Okazaki-Fragment-prelim.png
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DNA polymerase can only use nucleotides to synthesise DNA in a 5'-to-3' direction. Because the strands of the original DNA molecule point in opposite directions, on one strand, 5'-to-3' will point towards the replication fork, and on the other strand, 5'-to-3' will point away from the replication fork. Where it points towards the fork, DNA polymerase can just continually polymerise DNA in one long chunk, and this is the leading strand. Where it points away from the fork, it synthesises Okazaki fragments which begin at the fork and end at the previous Okazaki fragment.

Feel free to ask, if any of that was unclear or you have any further questions.
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Bertybassett
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Hi, i had a question on dna and was wondering if you could please help (a level). is the active site of dna polymerase complementary to the 5' end, and if so of what? the template or new strand? also, is the new strand made in the 5' to 3' direction (and the enzyme moves down the template strand in the 3' to 5' direction)?
(Original post by anosmianAcrimony)
The leading strand is synthesised in one long piece, whereas the lagging strand in synthesised in a bunch of smaller pieces called Okazaki fragments.

Name:  DNA-Okazaki-Fragment-prelim.png
Views: 23
Size:  4.3 KB

DNA polymerase can only use nucleotides to synthesise DNA in a 5'-to-3' direction. Because the strands of the original DNA molecule point in opposite directions, on one strand, 5'-to-3' will point towards the replication fork, and on the other strand, 5'-to-3' will point away from the replication fork. Where it points towards the fork, DNA polymerase can just continually polymerise DNA in one long chunk, and this is the leading strand. Where it points away from the fork, it synthesises Okazaki fragments which begin at the fork and end at the previous Okazaki fragment.

Feel free to ask, if any of that was unclear or you have any further questions.
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studyr
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DNA Polymerase is complementary to the 3' end of new strand I think
(Original post by Bertybassett)
Hi, i had a question on dna and was wondering if you could please help (a level). is the active site of dna polymerase complementary to the 5' end, and if so of what? the template or new strand? also, is the new strand made in the 5' to 3' direction (and the enzyme moves down the template strand in the 3' to 5' direction)?
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anosmianAcrimony
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(Original post by Bertybassett)
Hi, i had a question on dna and was wondering if you could please help (a level). is the active site of dna polymerase complementary to the 5' end, and if so of what? the template or new strand? also, is the new strand made in the 5' to 3' direction (and the enzyme moves down the template strand in the 3' to 5' direction)?
DNA polymerase's active site isn't complementary to any part of DNA, i.e. it doesn't form base pairs with it. I'm not sure I understand what you're asking, there.

DNA polymerase moves along the template strand towards the template strand's 5' end, synthesising a new strand by adding individual nucleotides to the new strand's 3' end. Does that make sense?
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anosmianAcrimony
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(Original post by studyr)
DNA Polymerase is complementary to the 3' end of new strand I think
What do you mean by that?
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studyr
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In the textbook it states that dna polymerase is complementary to the 3' of the newly formed strand. I do a-level btw, so my level of knowledge isn't as advanced
(Original post by anosmianAcrimony)
What do you mean by that?
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anosmianAcrimony
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(Original post by studyr)
In the textbook it states that dna polymerase is complementary to the 3' of the newly formed strand. I do a-level btw, so my level of knowledge isn't as advanced
Huh, I wouldn't have described it that way. I'd say it binds the 3' end of the newly formed strand and adds to it, but not that it's complementary to it. Usually I only use that word to describe nucleic acids (i.e. DNA and RNA) that bind each other in the very specific way that nucleic acids can.
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Reality Check
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(Original post by studyr)
In the textbook it states that dna polymerase is complementary to the 3' of the newly formed strand. I do a-level btw, so my level of knowledge isn't as advanced
DNA Pol is an enzyme. It isn't 'complementary' to anything!
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studyr
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Could you say it's specific ? Or nah
(Original post by Reality Check)
DNA Pol is an enzyme. It isn't 'complementary' to anything!
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Reality Check
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(Original post by studyr)
Could you say it's specific ? Or nah
anosmianAcrimony - I don't want to hijack your answers, so over to you
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studyr
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Could you say it's specific?
(Original post by anosmianAcrimony)
Huh, I wouldn't have described it that way. I'd say it binds the 3' end of the newly formed strand and adds to it, but not that it's complementary to it. Usually I only use that word to describe nucleic acids (i.e. DNA and RNA) that bind each other in the very specific way that nucleic acids can.
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anosmianAcrimony
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(Original post by studyr)
Could you say it's specific?
DNA polymerase can only add nucleotides to a 3' DNA end, so it is specific in that sense, but how it becomes attached there is actually a bit more complicated. There are other enzymes involved in loading it onto DNA that needs to be replicated, and still more enzymes involved in creating an RNA primer that it can begin from (as occurs with every Okazaki fragment on the lagging strand). I recommend you just learn what your textbook says about it, lest I give you ideas that are beyond the scope of the A-Level course.
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studyr
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Oooh thank you for the clarification !

(Original post by anosmianAcrimony)
DNA polymerase can only add nucleotides to a 3' DNA end, so it is specific in that sense, but how it becomes attached there is actually a bit more complicated. There are other enzymes involved in loading it onto DNA that needs to be replicated, and still more enzymes involved in creating an RNA primer that it can begin from (as occurs with every Okazaki fragment on the lagging strand). I recommend you just learn what your textbook says about it, lest I give you ideas that are beyond the scope of the A-Level course.
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anosmianAcrimony
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(Original post by studyr)
Oooh thank you for the clarification !
You're welcome!
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