DNA replication Flashcards
importance of retaining one strand
ensures genetic continuity between generations
genetic continuity - ensures the new cells inherit all of their genes from their parent cells.
important because cells in our body are replaced regularly
Replication of DNA and cell division also occurs during growt
Process of Semi conservative replication.
occurs in preparation of mitosis.
number of DNA molecules in parent cell must be doubled.
occurs during S phase (during interphase when the cell is not dividing)
helicase unwinds the DNA and breaks hydrogen bonds between the base pairs - forms 2 single polynucleotide DNA strands
each strand = template for new strand formation
new strand is made of free nucleotides wich are attracted to the exposed DNA bases by complimentry base pairing.
These new nucleotides are then joined by DNA polymerase
catalyses condensation reactions to form new strand.
strands join by hydrogen bonding between base pairs
Semi-conservative because half of the origional DNA molecule is conserved.
DNA polymerase
only adds nucleotides in 5’ to 3’ direction.
evaluating the Watson-Crick Model.
bacteria grown in broth containing heavy 15N nitrogen isotope
DNA contains Nitrogen in it’s bases
as bacteria replicate, they use the nitrogen from broth to make new DNA nucleotides.
after a while, all bacteria have DNA containing 15N nitrogen.
A sample of DNA from the 15N DNA then extracted and spun in centrifuge.
- this shows DNA containing heavy nitrogen settled near bottom of the centrifuge tube
bacteria containing only 15N DNA taken out of 15N broth and added to the broth containing only the lighter 14N nitrogen
the bacteria were left for one round of DNA replication
if semi-conservative replication had occured, all of the DNA molecules would now contian both the heavy 15N and light 14N nitrogen and would therefore settle in the middle of the tube.
The test confirmed that the bacterial DNA had undergone semi-conservative replication.
