DNA Replication Flashcards
What does DNA helicase do?
Breaks the hydrogen bonds between bases and unwinds the double helix.
The fact that DNA has a double helix allows both strands to act as what?
A template for semi conservative replication.
After the helix has been unwound, how do new nucleotides join the bases on the template strands?
Free floating nucleotides in the nucleus attract to exposed bases by complimentary base pairing.
What does DNA polymerase do?
Joins the free floating nucleotides to the template strand by condensation to create a new sugar phosphate backbone.
What does semi conservative replication mean?
Each new DNA molecule formed contains one original template strand.
Why is semi conservative replication important?
Ensures genetic continuity between generations.
How does DNA polymerase work to add nucleotides to a molecule?
It works backwards by adding nucleotides to the phosphate (‘3) end of the developing strand.
State the direction DNA polymerase works in, in terms of carbon.
(5’) to (3’)
When finding evidence for semi conservative replication, what was the bacteria grown in?
How does the nitrogen get inside the bacteria?
Heavy nitrogen (15N) for several generations.
The nitrogen incorporates into the bacterial DNA bases.
Where is the bacteria transferred to allow it to grow and divide twice?
The bacteria containing heavy nitrogen in transferred to a light nitrogen solution (14N)
Describe how the DNA is extracted from the bacteria.
The bacteria are spun at a very high speed in a centrifuge
If the DNA from the bacteria was grown for several generations in 15N solution describe the strands of DNA in the first sample.
DNA molecules contained 2 heavy strands, which have 15N incorporated into them.
In the 2nd sample, the bacteria grown in a 15N solution was then transferred for 1 division to a 14N solution. Describe the DNA strands.
DNA molecules contained 1 original heavy 15N strand and 1 new light strand 14N
In the 3rd sample, DNA from bacteria grown originally in 15N was transferred for 2 divisions to a 14N solution.
50% of DNA molecules contain 1 original heavy strand and 1 new light strand.
50% contained both light strands.
