BIOL 2104 Lecture Notes - Lecture 3: Okazaki Fragments, Semiconservative Replication, Radionuclide

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13 Jan 2018
Course
Professor
Module 3
DNA is the genetic material
Replicate faithfully
Having the coding capacity to generate proteins and other products for all cellular
functions
A genetic material must carry out two jobs: duplicate itself and control the development
of the rest of the cell in a specific way.
Meselson-Stahl experiment
Said DNA replication is semi conservative
They used radio isotopes
Heavy goes to bottom light goes to top
And when mixing both you have both heavy and light
One has old strand and one with new
John Cairns showed that initial unwinding is localized to a region of the bacterial circular
genome, called origin or ori
It is either unidirectional or bidirectional replication
o Bidirectional is faster
He grows bacterial cells for generation and incorporates into new DNA
and adds a lot of thymidine
He purifies the DNA and puts I into a coverslip and after 2 months
In bidirectional both sides have a heavy density label with the light in
between and heavy on the other side
After finding the film he finds two ends with a strong signal
Both areas are being replicated
Outcome
o Dna replication is semiconservative
Each strand of both replication forms is being copied
o Dna replication is bidirectitonal
Bidirectional replication involves two replication forks, which move in
opposite directions
o Dna is semidiscontiuous
Leading strand copies continuously
Lagging strand copies in segments which is later joined
Arthur Kornberg (1957)
First person to identify DNA polymerase I which is an enzyme that synthesizes DNA
He took protein extracted from E.coli
o And added a template a dna and monitored dna synthesis
o He added dNTPs (substrates) all 4 at once
o ATP (energy source)
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