Bev A. Kupf bevakupf at
Tue Jul 22 08:38:31 EST 2003

On 22 Jul 2003 06:08:40 -0700,
    Unterholzner Martin (h9540395 at wrote:
> Does the replication always start from the same end of the chromosome
> or is this facultative? For example: I have one chromosom with a dna
> douple helix:
> 5'-------------------3'
> 3'-------------------5'
> There are 2 posibilities to start the replication. Once from left to
> right or from right to left. From this decision dipends also which one
> is the leading or the lagging strand. My question is, if the origin of
> replication(ori)also gives  the directions of the replication or can
> the direction change from time to time? If the direction can change,
> the terminology of leading and lagging strand is vague. Propably that
> was  the confusing factor.

I think you need to read a little more about replication origins on
eukaryotic chromosomes.  There are hundreds of origins per chromosome.
Firing of each origin results in two leading strands and two lagging

Telomeres are at the end of chromosomes.  Each end has one strand that
ends in a 3'-OH.  That is the "G+T" strand, or the leading strand.  The
other strand is the lagging strand.

Hopes this clarifies things.

Bev A. Kupf
Bev's House of Pancakes

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