DNA Polymerase?

[raid517]

Hi, in this video this guy appears to be implying that one single DNA polymerase molecule is responsible for the process of copying DNA. (I may however be reading him wrong.)

 

 

He appears to imply that the DNA polymerase simply 'hops' back and forth across the two strands of the DNA molecule as DNA Helicase separates the two different strands. But surely it would make more sense and be more efficient if the replication process occurred using two separate polymerases? Since DNA polymerase 1 is progressive/semi-processive and DNA polymerase III is highly processive, wouldn't it be better to have these two enzymes do the two jobs separately at the same time? Also since there is 1 and 3, where does DNA polymerase 2 fit into the picture?

Edited January 28, 2012 by raid517

[raid517]

If you look at 23:25 onwards you will get a better idea of what he's saying. However every other video and animation I have seen say that there are two separate DNA polymerases that work to transcribe the leading and lagging strands. So which of these versions of events is accurate? Maybe its a dimer of some kind requiring the action of two joined (how though?) subunits of DNA polymerase? Surely this guy has got it wrong?

Edited January 28, 2012 by raid517

[Sukie S]

Hi,

 

As far as I understand, this topic is about DNA replication when organisms copy their number of DNA. This process normally happen during cell division. (Please don't confuse this with transcription and translation)

 

I think the DNA polymerase III haloenzyme that you mentioned is part of the multisubunit assembley of protein complexed in E.coli . It is also known as replisome, not to be confusing with the name DNA polymerase which is enzyme.

 

http://en.wikipedia.org/wiki/Replisome

 

 

I will summarise the process of DNA replication briefly in here too. I hope it will make it much more clearer so you can of polymerase in this process.

 

For DNA replication to happen, it requires necessary enzymes/protein complexes. The main enzymes are:

• Initiator protein
• DNA helicase : unwinding the double helix
• DNA polymerase(There are 6 different family A, B,C, D, X, Y and RT) : synthesis the nucleotides in the exonuclease 5'to 3' direction
• RNA polymerase (different types depend on prokaryotes or eukaryotes) Main types in eukaryotes are I, II and III
• Topoisomerase
• Telomerase
• DNA ligase

Stage of DNA replication

 

1.initiation : the initiator protein open the double strand DNAand recruite helicase to unwind the double stranded DNA

: once the single-strand DNA is formed, the SSB protein ( single stranded binding proteins)

: initiation is very restricted and happens only once per cell division.

 

2.elongation : Once initiation starts, and the replication machinery is in place, replication start.

: By this time, DNA double strand are seperated into leading strand and lagging strand.

* : DNA polymerase can only added nucleotide to the 3' end of the strand, it required short stretch of RNA primer at the start.

: RNA primer is degraded.

: two protin complexes involves for elongation : clamp loader and sliding clamp

:Because DNA can only be synthesised in the 5'to 3' direction, if this happens both strand of DNA will be synthesied into opposite direction. To overcome this problem the lagging strand is synthesis in a short stretch called Okazaki fragment and joined into continuous strand. Enzyme DNA ligase can link the pieces of DNA together.

 

3.termination : depend on type of chromosome ( if it is linear or circular)

 

 

I hope this can help you understand this process more.

 

 

[raid517]

Yeah that's a really great effort thanks. But I kind of had most of that already. The confusion is in what this guy in the video says at around 23:20 onwards, where he implies that one single DNA polymerase III is responsible for encoding both the leading and lagging strands. I just want to know if this is accurate, and if so how this can be the case? I suspect he's wrong, or at least I have been unable to source any video, or any animation showing how this might work. Instead most show two (or more) separate DNA polymerases encoding the leading and lagging strand simultaneously, all be it in a processive (for the leading strand) and (semi-processive) for the lagging strand) way.

 

Can anyone explain if he is right how this is the case, or maybe find a video or animation of this process in action?