Dna Half-Independent Lab Report

Radioisotopic labels would be used in experiments to identify semi-conservative replication in prokaryotes. Because we anticipated that a labeled DNA would have different density with unlabeled, which means, by analyzing the different density of DNAs, we can determine which of DNA is labeled, half-labeled or unlabeled. To this end, I will use c13 label the bacteria and abruptly change carbon source with C12. Then I will collect four samples in different time and analyze the results from centrifugal by ultraviolet absorption.

According to the hypothesis above, I design the experiment below.

Firstly, Escherichia coli B will grow 14 generations at 36° C. with aeration in a glucose salts medium which is the only carbon source and labeled with C13. Then I will abruptly change the only carbon source from labeled with C13 to C12. At the same time, I also add ribosides with only C12 into the medium to make sure subsequent growth is in the medium of a tenfold excess of glucose with C12 containing ribosides.
Each sample was immediately chilled and centrifuged in the cold for 5 minutes at 1800*g. After resuspension in 0.40 ml of a cold solution 0.01 M in NaCl and 0.01 M in EDTA at pH6, I use 0.1 ml of 15 per cent sodium dodecyl sulfate to lyse cells and store these samples in