Lesson 17: DNA Replication 1 Flashcards
what are the enzymes that replicate DNA
DNA dependent DNA polymerases
what kind of pathway is replication
an anabolic pathway
meselson-stahl experiment
3 competing models of DNA replication
what were the 3 proposed models of replication
semiconservative, conservative, dispersal
semiconservative results
1/2P:D and 1/2 D:D
one daughter DNA molecule sis all new and the other is all old DNA
conservative model results
3/4 D:D and 1/4 P:P
each daughter DNA molecule contains a mixture of old and new DNA
dispersive model results
all increasing ratios of D/P
each daughter DNA molecule contains one new strand and one old strand
meselson-stahl experiment control 1:
grow cells in “heavy” isotope of Nitrogen (N15) –> WHY –> bacteria can make all N-bases; therefore, all DNA will be heavy DNA
- density of heavy DNA was about 1.724
meselson-stahll experiment control 2:
grow cells in light isotope of Nitrogen, thus the DNA will be light DNA
– density of light DNA is 1.710
meselson-stahll experiment step 1:
grow cells in N15 and allow to replicate – then shift cells to a media containing N14. RESULT::
density was 1.717 –> in the middle of light and heavy DNA density
after 1 round of relication for the meselson-stahl experiment –
conservative can be discaded
– if conservatie then we would expect 2 peaks (1 heavy and 1 light) – so therefore the mechanism can be dispersive or semi
meselson stahl - experiment step 2:
allow cells to replicate one more time in the media containing N14
– found 2 peaks – one N14:N14 and one N14:N15
—- must be semi conservative
what would happen to the intensity of each of the peaks as replication is allowed to continue in the media containing N14
- the light DNA peak will increase in intensity as replication continues
- the intensity of the hybrid DNA will decrease relative to the light DNA but will NEVER dissappear
