Mohammad Ahmed Hotiana (17-10532)
BIOT 313 (Molecular Biology)
THE REPLICATION OF DNA IN ESCHERICHIA COLI
By Mathew Meselson & Franklin W Stahl
Biology Vol. 44, 1958
Deoxyribonucleic acid (DNA) molecules are responsible for the transfer of hereditary
information from one generation to another. DNA replication is the process by which DNA
molecules replicate to produce identical copies that are to be transferred to the daughter cells.
Because of its long history as a sample organism for many biological experiments and its ability
to replicate at a fast rate under normal conditions, researches used Escherichia Coli bacteria for
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01 M in NaCl and 0.01 M in
ethylenediaminetetra-acetate (EDTA)] at pH 6, the cells were lysed by the addition of
0.10 ml of 15 per cent sodium dodecyl sulfate and stored in the cold.
(Note: These conditions were introduced to make sure the cell is destroyed while preserving the
molecules under concentration, DNA. EDTA was used as a metal scavenger, making sure no
available metal takes part in any reaction)
(As a result of this centrifugation a density gradient is established and molecules settle at
different positions in accordance to their densities)
0.010 ml of the dodecyl sulfate lysate was added to 0.70 ml of CsCl solution [buffered at
pH 8.5 with 0.01 M tris aminomethane]. The density of the resulting solution was 1.71
gmcm-3. This was centrifuged at 44,770 rpm for 20 hours, until the DNA had reached
Isolated bands of DNA were observed at a region of density 1.71 gmcm-3.
Microdensitometer was used to obtain ultraviolet absorption photographs for each
For the F1 (one generation time) generation, the band observed was in-between the bands for
N14 and N15. This shows that only...