Topic 2.7 - DNA replication Flashcards
DNA replication is semi-conservative which means that…
One strand is from an original template molecule and one strand is newly synthesised
Why is DNA replication semi conservative ?
This occurs because each base will only pair with its complementary partner and thus ensure the sequence is conserved
Cite the two enzymes responsible for helping DNA replication happen ?
Helicase and Polymerase
What is the function of helicase ?
Unwinds and separates the double stranded DNA
Breaks the hydrogen bonds between the base pairs
What is the function polymerase ?
Free nucleotides line up opposite complementary partners
DNA Pol III covalently joins the free nucleotides together
What experiment supported the theory that
DNA replication occurred via a semi-conservative process ?
The Meselson-Stahl experiment
How was the experiment realised ?
They incorporated radioactive nitrogen isotopes into DNA
* Templates were prepared with heavier 15N
* New sequences were replicated with lighter 14N
The DNA was then separated via centrifugation in order to determine its composition of radioisotopes
* 1st division: DNA had 15N and 14N (i.e. mixed)
* 2nd division: DNA is mixed or has 14N only
What was the result of the experiment ?
The results were consistent with a semi-conservative model
What is the Polymerase reaction chain ?
The polymerase chain reaction (PCR) is an artificial method of DNA replication that is used to rapidly copy sequences
How does PCR occur ?
PCR occurs in a thermal cycler over three repeating steps:
* Denaturation: DNA heated in order to separate strands
* Annealing: Primers attach to ends of a target sequence
* Elongation: A heat-tolerant polymerase copies strands
