telomeres

Replication fork -  http://en.wikipedia.org/wiki/Telomere. Organisms with linear chromosomes have to solve the problem that DNA replication makes them shorter. This is due to the fact that DNA polymerase can only add bases to the terminal 3'-OH of a DNA chain. The DNA replication initiation complex uses RNA primers to provide the initial 3'-OH and to initiate "lagging" strand synthesis.  While one strand can be copied all the way to the end of a chromosome, the other, lagging strand, must be primed at short intervals in order to provide a 3' OH group for DNA polymerase as the replication…