2.2 DNA Replication Flashcards
What are the requirements for semiconservative DNA replication?
~ both strands of DNA must act as a template for the attachment of nucleotides
~ the enzyme DNA polymerase must be present
~ a source of chemical energy must be used to drive the process
What is the process of DNA semiconservative replication?
~ DNA Helicase breaks the hydrogen bonds between bases, as a result, the double helix unwinds and separates into two separate strands
~ each strand of polynucleotide acts as a template for the new nucleotides to attach onto by specific base pairing
~ nucleotides are joined together in a condensation reaction with DNA polymerase to form the missing poly nucleotide strand
~ each of the new daughter DNA molecules contains one of the original parent strands and 1 new synthesised strand
What evidence is there for semi conservative DNA replication
Meselsohn and stahl did an experiment that consisted of:
~grow bacteria on N15 medium - extract the DNA from that bacteria and place it in a special solution
~ ^^ DNA Extracted gets placed in a centrifuge
~the bacteria was then grown in a N14 medium for many generations
~ ^^ DNA Extracted gets placed in a centrifuge
~bacteria was transferred to a N14 medium and samples were removed and observed
What medium was used to label the original DNA of bacteria?
They labelled the original DNA of bacteria by growing them on a medium of 15N.
What medium did they transfer the bacteria to for replication?
They transferred the bacteria to a medium of 14N for a single generation to allow it to replicate once.
What determined the mass of each ‘new’ DNA molecule?
The mass of each ‘new’ DNA molecule would depend upon which method of replication had taken place.
How did they separate out the different DNA types?
They centrifuged the extracted DNA in a special solution.
Where did lighter DNA collect in the centrifuge tube?
The lighter the DNA, the nearer the top of the centrifuge tube it collected.
Where did heavier DNA collect in the centrifuge tube?
The heavier the DNA, the nearer the bottom of the tube it collected.
How many generations of DNA were analysed?
They analysed the DNA after two, then three, generations.
What could they determine by interpreting the results?
By interpreting the results they could determine which hypothesis was correct.
What experiment was investigated for the proof of semi conservative replication
Meselsohn and stahl labelled the original DNA of bacteria by growing them on a medium
of 15N. They then transferred the bacteria to a medium of 14N for a single generation to allow it to replicate once. The mass of each ‘new’ DNA molecule would depend upon
which method of replication had taken place.To separate out the different DNA types, they centrifuged the extracted DNA in a special solution. The lighter the DNA, the nearer the top of the centrifuge tube it collected.The heavier the DNA, the nearer the bottom of the tube
it collected.
What is conservative replication?
The original parent DNA molecule remained intact and a separate door to DNA. Copy was made from new molecules of nucleotides. Out of the two molecules produce one would be made of entirely new material and the other would be 100% original material.
What results were concluded from the nitrogen experiment
G0- both strands were heavy and contained N15 ( settled lower in test tube)
G1- one heavy strand (N15) one light strand (N14) = mixed DNA molecule ( settled in the middle of test tube)
G2- one mixed DNA molecule and one light DNA molecule ( one settled midway N14N15 and other settled higher N14) 50-50
G3- more N14 DNA molecules settled higher than N14N15 molecule - 75-25
