Question

6.      How is an eukaryotic chromosome replicated?  How many start points or origins are found on an eukaryotic chromosome and does replication proceed from in one direction or in both directions from each origin?  

Answer 1

eukaryotic chromosomes are linear, regions, where DNA replication starts, is called the origin of replication, DNA melts at the origin of replication and then helicase separates the two strands of DNA, primase adds primer and the DNA polymerase adds new nucleotides to the 3` OH of the primer, nucleotides are added complementary to that in the template strand, the synthesis of DNA in the template strand having polarity 3` to 5` is continuous and in the other template strand DNA is replicated as small fragments. to completely replicate the DNA there are multiple origins of replications even within a single linear chromosome. there are 400 origin of replication in yeast and 30000- 50000 origins of replication in humans, the number fo origin of replications is different according to the genome size.

at replication bubble 2 replication forks are generated, it moves in opposite directions, so DNA replication is bidirectional.

the enzymes used in the eukaryotes are different from that in the prokaryotes, the DNA polymerase, Helicase are all different, but they function similar to that in prokaryotes.