DNA Polymerase Directionality and Independence in Eukaryotic Replication

[student007]

In eukaryotes, DNA polymerase works in one direction only. Does that mean that one enzyme works simulteneously on both new strands, or is there on polymerase working on each strand. If the latter is true, then the two strands are independent of each other in a sense. If so, which polymerase governs which direction it moves, and why can't they move in opposit directions to simplify and speed up the process (this would eliminate the lagging strand)?

 

[quetzalcoatl9]

In eukaryotes, DNA polymerase works in one direction only. Does that mean that one enzyme works simulteneously on both new strands, or is there on polymerase working on each strand. If the latter is true, then the two strands are independent of each other in a sense. If so, which polymerase governs which direction it moves, and why can't they move in opposit directions to simplify and speed up the process (this would eliminate the lagging strand)?

it works on both strands simultaneously, on both forward and lagging strand. this improves the fidelity of replication since a mismatched base can be detected before the replication bubble moves very far.

 

[quasi426]

DNA replication is bidirectional meaning that there are TWO lagging strands and TWO leading strands during replication. In prokaryotes there is usually one origin of replication while eukaryotes require many more origins of replication since eukaryotes have genomes that are much larger.

 

[student007]

So in a nutshell:
Eukaryotes: 1 polymerase synthesizing both strands simultaneously (a leading and lagging strand)
Prokaryotes: 2 polymerases, one per strand, that proceed in opposite directions (hence no leading or lagging strands)

 

[iansmith]

Eukaryotes: 1 polymerase synthesizing both strands simultaneously (a leading and lagging strand)

At least 2 polymerase per origin of replication. Polymerase can only synthesise one strand at a time in the 5' to 3' direction. The lagging strand is the one that is unzipping from the 5' to the 3' direction

Prokaryotes: 2 polymerases, one per strand, that proceed in opposite directions (hence no leading or lagging strands)

There 2 polymerase (it might be up to 4 polymerase) but there is a leading and lagging strand.

For good visual aid, http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DNAReplication.html

 

[student007]

but how is there a lagging strand in prokaryotes if the polymerase can move in different directions on prokaryotes?

 

[iansmith]

but how is there a lagging strand in prokaryotes if the polymerase can move in different directions on prokaryotes?

In bacteria, the polymerase only synthesise in the 5' to 3' direction. Same as with eukaryotes.

 

[quasi426]

Most prokaryotic organisms have circular chromosomal genome DNA.

 

[student007]

so the same polymerase that catalyzes one new strand catalyzes the other as well, with prokaryotes too. therefore, with prokaryotes, there Is a lagging strand. makes sense (i hope I'm right)

 

[quetzalcoatl9]

since dna always has a 5->3 strand, and another complementary strand going 5->3 in the opposite direction, replication is bidirectional (for both strands) for both prokaryotes and eukaryotes.

eurkaryotes typically have multiple origins of replication (aka "ori") whereas prokaryotes have fewer. what happens if both polymerases going in different directions smash into each other? also, what happens when there's a collision with the transcriptional machinery?

also, prokaryotes have a circular chromosome, so the replication system is complete. but what happens when you have a linear chromosome (as eukaryotes do) and the polymerase gets to the end? what happens to the lagging strand replication? (hint: telomeres)

 

[student007]

i know...it gets shorter on both sides, as the primer must be removed but no more nucleotides can be added to the 5' end.