2.4.1 - DNA Replication Flashcards
What Is The Importance Of DNA Replication?
(4 Points)
~ Before a parent cell divides, it needs to copy the DNA contained in it.
~ Doubling the DNA ensures that the two new daughter cells produced will receive full copies of the parental DNA.
~ Occurs in preparation for mitosis.
~ Occurs in the S phase of the cell cycle.
How Does DNA Replicate?
(4 Points)
~ Via semi-conservative replication.
~ As in each new DNA molecule produced one of the polynucleotide DNA strands is from the original DNA molecule being copied.
~ The other polynucleotide DNA strand has to be newly created by the cell.
~ Therefore, the new DNA molecule has conserved half of the original DNA and then used this to create a new strand.
What Is The Importance Of Retaining One Original DNA Strand?
(2 Points)
~ Ensures that there is genetic diversity between the generations of cells.
~ Important because cells in our body are replaced regularly and therefore we need the new cells to be able to the same roles as the old ones.
Describe The Process Of DNA Replication (Semi-Conservative Replication)
(5 Points)
1) Enzyme DNA helicase unwinds the DNA double helix by breaking down the hydrogen bonds between the base pairs on the 2 antiparallel polynucleotide DNA strands to form 2 single polynucleotide strands.
2) Each of these single polynucleotide strands act as a template for the formation of a new strand made from free nucleotides, that are attracted to the exposed DNA bases by complementary base pairing.
3) Condensation reactions join the new nucleotides together by the enzyme DNA polymerase.
4) The original strand and the new strand join together through hydrogen bonding between the base pairs to form the new DNA molecule.
5) Each new DNA molecule contains one strand from the original DNA molecule and one new strand.
Describe The Role Of DNA Polymerase In DNA Replication
(3 Points)
~ Synthesises new DNA strands from the two template strands.
~ By catalysing condensation reactions between the deoxyribose sugar and phosphate groups of adjacent nucleotides within the new strands, creating the sugar-phosphate backbone of the new DNA strands
~ Breaks off the two extra phosphates and uses the energy released to create the phosphodiester bonds.
What Was The Point Of Meselson & Stahls Experiment?
(2 Points)
~ Scientists were unsure if DNA replication was conservative or semi-conservative.
~ Conservative -> The original DNA strands would stay together and the new DNA molecules would contain two new stands.
What Did Meselson & Stahls Experiment Show?
(3 Points)
~ Showed that DNA is replicated using the semi-conservative method.
~ They did this by experimenting with isotopes of nitrogen, as DNA contains nitrogen.
~ They used heavy nitrogen (15N) and light nitrogen (14N).
Describe Meselson & Stahls Experiment
(8 Points)
1) Two samples of bacteria were grown, one in a nutrient broth containing 14N and on in a nutrient broth containing 15N.
2) As the bacteria reproduced, they took up nitrogen from the broth to make new DNA nucleotides, so the nitrogen gradually became apart of the bacterias DNA.
3) A sample of DNA was taken from each batch of bacteria, and spun in a centrifuge. DNA from 15N settled lower down in the centrifuge than the 14N DNA.
4) The bacteria grown in the 15N broth were taken out and put in the 14N broth. The bacteria were left for one round of DNA replication, then another sample of DNA was taken out and spun in the centrifuge.
5) If DNA replication was conservative, the original 15N DNA would settle at the bottom and 14N DNA at the top.
6) If DNA replication was semi-conservative, the new bacterial DNA molecules would contain one strand of the old 15N DNA and one strand of the new 14N DNA. So DNA would settle towards the middle of the tube.
7) As it turned out, the DNA settled out in the middle, showing that the DNA molecules contained a mixture of 15N and 14N.
8) The bacterial DNA had replicated semi-conservatively in the 14N.
