DNA replication

[Greenspin]

Hi guys,

 

I was wondering if I could gt some help filling in some fundamental grey areas in my understanding of DNA replication?

 

 

DNA replication - eukaryotic (going to write my hazy understanding of the process)

 

 

a. Numerous origins of replication; DNA helicase binds here and unwinds helix whilst breaking hydrogen bonds between bases - single stranded binding proteins attach.

 

- Major point of confusion

 

- What initially melts the double helix?

 

- What signals helicase to bind?

 

- Are all points of origin the same sequence (well the same two complimentary sequences)

 

- At what point does topoisomerase bind?

 

- I thought helicase was bound round one of the strand and not the other, so does it open up then close again once around a single strand?

 

 

b. RNAprimase binds, synthesises an RNA primer and dissociates again

 

- How does it know to do this, and where to do this - especially on the lagging strand?

 

 

c. DNAP III binds to the primer and starts synthesising a leading and lagging strand

 

Lagging strand:

 

- Primase binds, synth primer, dissociates

- DNAP III synth, dissociate

- RNase H catabolises RNA primer <--- is RNase H a part of DNAP I (I keep seeing it written that DNAP I does this job?)

- DNAP I fill gap where RNA primer was - also has 5'-3' exonuclease activity to remove any remaining RNA nucleotides

- Ligase joins gaps between Okazaki fragments

 

- repeat

 

- is this set of enzymes (including the helicase, topoisomerase, and enzymes synthesising the leading strand) the 'holoenzyme'? Is this also called the 'origin recognition complex'?

 

 

d. At some point the leading and lagging strands of various replication forks must meet, so do the leading strands just join up as per the lagging stands?

 

e. The initial RNA primer of the leading strand is catabolised by RNase H, hence shortening of telomeres

f. The last primer added to the lagging strand is catabolised, hence shortening of the telomere of the lagging strand

 

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DNA Replication - prokaryotic

 

Same as above, but but no replication bubble, just two point of replication

 

- Is there a lagging strand? I assume not..

 

 

Many thanks to anyone who can give me a a hand here.