Why is DNA replicated 5' to 3'?

Discussion of the reaction mechanism for DNA (and RNA) synthesis, and why it causes synthesis to proceed only in the 5' to 3' direction. Images from this video are CC licensed and available at http://www.flickr.com/photos/agathman/sets/72157617475156596 .

Category:

Education

Tags:

• DNA
• synthesis
• genetics
• RNA
• polymerase
• DNA replication

[beccalishass]

so in a nutshell, 5 prime end has a favourable leaving group (O) and therefore.........still a tad lost

[agathman]

@beccalishass 5' end of the INCOMING dNTP has a good leaving group (PP). If you're going to join 5' to 3', that means the incoming dNTP has to add on to the 3' end of the existing strand.

[GJEViLakaTHEKING]

also, if you would take a look at my other conclusion regarding the ribosomes, it would be great too. here goes,

Ribosomes read the mRNA from 5' to 3'. They do this by attaching to AUG on the 5' end of the mRNA molecule. They then read all the way till a stop codon is found. The Anticodon (on the tRNA) must be complementary to this, so it must be read from 3' to 5'. That is the anticodon for 5' AUG 3' is 3' UAC 5'.

[agathman]

@GJEViLakaTHEKING Yes, absolutely. Anticodons are the one exception to the rule that nucleic acid sequences are given 5' to 3' -- generally we state anticodon sequences 3' to 5', so we'd say the methionine anticodon (pairs with AUG) is UAC. Normally you'd say CAU, since that's 5' to 3', but it would be confusing to say it that way.

[GJEViLakaTHEKING]

You Explain things like an amazing Boss. It would be great if my university hired you as a prof!

I always have a hard time understand with the directions, so THANKS!

in video's conclusion,

DNA polymerase reads the template strand from 5' to 3' direction, BUT adds the nucleotides to a open 3'OH group so it attaches from 3' to 5'. It makes the rna molecule starting at 3' towards 5'.

the same is true for rna polymerase (I think)

[agathman]

@GJEViLakaTHEKING -- I think you're misstating the conclusion. DNA polymerase (or RNA polymerase) moves along the template strand in the 3' to 5' direction (as seen from the template strand). The newly synthesized nucleic acid strand is antiparallel to that template, and is made by adding nucleoside triphophates to the 3' end of that new strand. Thus the new strand grows in the 5' to 3' direction. The 5' end of, for instance, an RNA molecule is made first; the 3' end is made last.

[moonshadow285]

Thank you so much! My professor neglected to draw out the structures for why 3`-->5` wouldn't work so it was very confusing!

[Haatpiraat]

Thanks a lot for your video, it is clear to me now!

[bluskish]

Do you teach microbiology too? (I would commute, from WA) Your lecture style is so clear to me, thank you for posting these videos.

[Oneironosus]

@agathman In regards to why 3' to 5' addition of nucleotides isn't seen, only 5' to 3' replication allows efficient error correction. If the pyrophosphates are cleaved from the base already incorporated(as in 3' to 5'), if an an error is detected and the exonuclease removes one base, the phosphates required for the correct base to be added have already been cleaved away, they can not come from the new base.Thus further strand synthesis couldn't occur. So proofreading is likely a good reason too.

[Ranjithlove1992]

Thank to you for your teaching it's very brilliant and great i can understand this i said onemore time thank you very much Mr.Agathman

[TheShikobe]

Excellent explanation Sir! Only wish the video quality was abit better...

[VashaB]

This video is by far the most amazing video on DNA replication I have ever seen. Everything makes sense now. Thanks you so much!