-DNA helicase breaks hydrogen bonds between complementary bases
-This creates two templatestrands
-Free DNAnucleotides are attracted to their complementarybasepair and hydrogen bonds form
-DNA polymerase forms phosphodiester bonds between adjacent nucleotides
-This is semi-conservative replication
Why does semi-conservative replication only occur in the 5' to 3' direction?
DNA polymerase is only complementary to 3' end
It is not complementary to the 5' end
Can only add new nucleotides to the 3' end of the strand
Not the 5' end of the strand
Describe the semi-conservative replication model by Meselson and Stahl
-Bacterial cells are grown in N-15 solution so all DNA bases have N-15. DNA is centrifuged and 1 band settles at the bottom of the tube (high density)
-Cells are transferred to N-14 and divide once. DNA is centrifuged and the band settles in the middle as all DNA had N-15 and N-14 (medium density)
-Cells divide again. 2 bands form, 1 in the middle and 1 at the top as some had N-15 and N-14 strands and some had only N-14 strands due to semi-conservativereplication
