BIOE 185 Lecture Notes - Lecture 5: Differential Centrifugation, Matthew Meselson, Franklin Stahl
Document Summary
Dna replication: different models, molecular details, and in vitro sequencing. The double helix model proposed by watson and crick led them to suggest a semi- conservative copying mechanism for dna. In short, watson and crick hypothesized that when a cell copies dna, each parental strand (here shown in red) serves as a template for a new, complementary strand (shown in blue). Thus, following one round of replication, each replicated dna molecule should consist of one strand of parental (i. e. , red) dna and one strand of the newly made (i. e. , blue) dna. Thus, only one strand of the original helix is (cid:498)conserved(cid:499). (owever, there were two other labeled with a heavy isotope of nitrogen, 15n (cid:523)(cid:498)nitrogen-(cid:883)(cid:887)(cid:499)(cid:524). Thus, all nitrogen these bacteria to a medium containing nitrogen in the normal 14n (cid:523)(cid:498)nitrogen-(cid:883)(cid:886)(cid:499)(cid:524) form, so that new dna stands would be synthesized with this lighter isotope. Dna can be separated from 14n-dna using density gradient centrifugation.
