Biology Lecture No. 18: DNA Replication
Wednesday March 14 , 2012
-Anti-parallel complementary base pairing allows for accurate replication.
-Replication is semi-discontinuous and semiconservative.
-Replication “bubble” arises from two “forks” created at one “origin.”
-Large, linear, eukaryote chromosomes have several origins.
Replication Forks Process Both DNA Strands:
-Both strands are replicated in the same replisome at the same time, very close together.
Elongation By DNA Polymerase:
-DNA synthesis proceeds by adding a new base to the 3’ OH of a properly-paired base.
-It is only possible to extend 3’ ends.
-RNA primase synthesizes RNA primers, which are extended by DNA polymerase III, and then DNA
polymerase I removes the primers and replaces them with DNA.
-Both strands have polymerases reading from the 3’ to 5’ end. They are being replicated by the same
-Replisomes replicate both strands at the same time by the same replisome. One strand is replicated
continuously; the other strand is replicated discontinuously.
The Leading Primer:
-The RNA primer on the leading strand is unable to be replaced with DNA by DNA polymerase I because
there is no 3’ OH.
-Since this primer on the leading strand cannot be replaced, the DNA result is becoming progressively
shorter as a result.
-It is important to note that polymerases always extend 3’ OH’s and that RNA polymerases can start
themselves, whereas DNA polymerases cannot. Telomeres & Telomerase:
-As RNA polymerase