|Okazaki fragment||medical dictionary|
All the known DNA polymerases can only synthesis DNA in one direction, from the 5' to 3' direction. However as the strands separate, replication forks will be moving along one parental strand in the 3' to 5' direction and 5' to 3' on the other parental strand. On the former, the leading strand, DNA can be synthesised continuously in the 5' to 3' direction. On the other, the lagging strand, DNA synthesis can only occur when a stretch of single stranded DNA has been exposed and proceeds in the direction opposite to the movement of the replication fork (still 5' to 3).
Such fragments were first observed by Okazaki using pulse labelling with radioactive thymidine. In eukaryotes, Okazaki fragments are typically a few hundred nucleotides long, whereas in prokaryotes they may contain several thousands of nucleotides.
(11 Jul 2010)
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