evidence for semi conservative replication Flashcards
why is DNA called semi conservative ?
in each new DNA molecule produced, one of the polynucleotide DNA strands (half of the new DNA molecule) is from the original DNA molecule being copied
why is maintaining one original DNA cell important ?
-genetic continuity through many generations
-insured new cells inherit all genes from their parent cells
-This is important because cells in our body are replaced regularly and therefore we need the new cells to be able to do the same role as the old ones
when did Watson and Crick do their thing ?
1953
what did watson and crick work on ?
confirming the double helix structure of DNA and coming up with a model for DNA replication
What did people think of Watson and cricks theory ?
it was just a theory , many people thought DNA replicated conservative
what does the theory of conservative replication suggest ?
the strands of the original DNA molecule would stay together, and the new, replicated DNA molecule would be made out of two brand new strands
who was Watson and cricks theory proved to be correct by ?
Meselson and Stahl
what is the first step of Meselson and Stahl?
Bacteria are grown in a broth containing the heavy (15N) nitrogen isotope
DNA contains nitrogen in its bases
As the bacteria replicated, they used nitrogen from the broth to make new DNA nucleotides
After some time, the culture of bacteria had DNA containing only heavy (15N) nitrogen
what is the second step of Meselson and Stahl?
A sample of DNA from the 15N culture of bacteria was extracted and spun in a centrifuge
This showed that the DNA containing the heavy nitrogen settled near the bottom of the centrifuge tube
what is the third step of Meselson and Stahl?
The bacteria containing only 15N DNA was then taken out of the 15N broth and added to a broth containing only the lighter 14N nitrogen. The bacteria were left for enough time for one round of DNA replication to occur before their DNA was extracted and spun in a centrifuge
If semi-conservative replication had occurred, all the DNA molecules would now contain both the heavy 15N and light 14N nitrogen and would therefore settle in the middle of the tube (one strand of each DNA molecule would be from the original DNA containing the heavier nitrogen and the other (new) strand would be made using only the lighter nitrogen)
What is the fourth step of Meselson and Stahl?
repeated step 3 and the DNA will contain 3 light strands and 1 heavy strand
