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  #1  
Old 09-18-2011
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DNA DNA Bidirectional Replication in UWorld!

plz clear this doubt....

"uworld says that bidirectional dna replication requires construction of two distinct strands of dna, and these strands are built in both 5 to 3 and 3 to 5 direction...which of the following is unique in 3 to 5 direction..."


can someone plz explain how is dns replication bidirectional???!!!!

this has got me going crazy!!!
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Old 09-19-2011
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"uworld says that bidirectional dna replication requires construction of two distinct strands of dna, and these strands are built in both 5 to 3 and 3 to 5 direction...which of the following is unique in 3 to 5 direction..."


Well, this is a property of both Prokaryotic and Eukaryotic cells.. basically, this is what happens:


You have a strand : 3' ----------------------------------------- 5'
5' ----------------------------------------- 3'

bidirectional means A fork will form somewhere in the middle (where there is RNA primers attach...one enzyme will read to the left (the bottom strand), the other enzyme will read to the right (up strand)

something like this:

3'-------------------- ------------------------5'
RNA Primer+DNA POLYMERASE ->
Lagging strand with okazaki

5' -------------------- ------------------------3'
<- DNA Polymeras+RNA Primers
Lagging strand with okazki

So, you can see, there are in fact 2 enzymes working...one goes to the right, one to the left, with subsequent copy of the up strand and down strand...

Later, a DNA ligase will join the strands together..

This is, what I understand..If I am wrong, please someone clarify...I may be wrong, but this is what I think BIDIRECTIONAL means...it not only means only the okazaki fragments..
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Old 09-19-2011
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Guys i believe its much simpler than you think!

At the origin of replication, the replication fork is formed, a region where active synthesis of DNA occurs. It moves along the DNA molecule as the two DNA strands unwind and seperate and synthesis occurs.

Bidirectional DNA replication is that the replication forks (in eukaryotic cells there are numerous origins of replication, so numerous replication forks) move in opposite directions from the origin. That's all!

Hope i helped! if still not clear post for more details...
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