Topic 12- DNA Replication Flashcards
Describe the Hershey Chase Experiment
Bacteriophages are made out of protein and DNA.
Protein has sulfur, DNA does not.
DNA has phosphorus, protein does not.
They grew two batches of bacteriophages, one with radioactive phosphorus, one with radioactive sulfur.
They then used those viruses to infect bacteria.
They shook the test tubes so the bacteriophages fell off and formed a pellet on the bottom and the phages floated to the top as a supernatant. They then tested it and found that the radioactive DNA entered the bacteria.
Describe the Structure of DNA
DNA is a double stranded Helix. One side goes from 5’ to 3’ while the other goes from 3’ to 5’.
The 5’ end ends with phosphate
The 3’ end ends with sugar
The who chains are connected by A-T bonds which are double bonds and G-C bonds which are triple bonds.
Describe how DNA is separated in replication
Helicase unzips the DNA starting at the Origin of Replication.
Slightly in front of it is the Topoisomerase what relieves strain on the helix preventing it from snapping.
Then behind the Helicase is the Single strand Binding protein that prevents the unzipped strands from binding with each other.
Describe how new DNA is made in replication
Primase makes a RNA primer at the origin.
DNA Polymerase 1 binds to the RNA primer and makes DNA in the 5’ to 3’ direction, aka 3’ to 5’ direction on the template.
DNA Polymerase 3 then replaces RNA Primer with DNA
Ligase then makes the final covalent bond between the newly made DNA segments.
Leading vs Lagging strand
The leading strand is when the DNA Polymerase goes the same direction as the helicase.
The lagging strand is when the DNA Polymerase goes the opposite direction as the Helicase.
- In this case the Polymerase makes a section then drops off and goes back to the newly unzipped region of DNA that the helicase opened up.
How does the cell check if the DNA was made correctly?
It does polymerase proof reading where a exonuclease cuts out the incorrect nucleotide.
What is the Origin of Replication?
Areas with a lot of A-T bonds because they are made of weaker double bonds.
