DNA Replication a strand of DNA serves as a template for replication: complementary strain Meselson & Stahl use density centrifugation to determine method of replication grew bacterial in two different weights of Nitrogen media so the nitrogen bases have different weights switched media ruled out conservative replication need to separate strands to determine determined semi-conservative method is the true method replication begins at origin of replication bacterial and yeast: typically begin at high concentration of A/T point because there are only two hydrogen bonds between Adenine and Thymine whereas Guanine and Cytosine have three hydrogen bonds between them origin is 100-150 bp long 11-nucleotide core sequence of adenine and thymine and flanking adenine and thymine regions