DNA Replication Flashcards
What happens at the start of DNA replication (strands)?
Each of the 2 strands are used as a template for new strands.
What enzyme unwinds and unzips the DNA double helix?
Helicase
What bonds are broken by this enzymes?
Hydrogen bonds
What is the starting point for the construction of a new strand of DNA?
A primer is the start of a new strand - catalysed by primase
What is the role of DNA polymerase?
o It binds the DNA nucleotides from the 5’ to 3’ end
o It also catalyses the formation of phosphodiester bonds between aligned nucleotides
What is the difference between the leading and lagging strand?
The leading strand is made continuously and the lagging strand is made in fragments (because its direction is 3’ to 5’)
What are the fragments from lagging strand called?
Okazaki fragment
What enzyme joins the strand together with H bonds?
DNA Ligase
What does it mean for a molecule to be semi-conservative?
A new DNA molecule comprises of one original template strand and one new strand.
How does the pairing of nitrogenous bases allow identical copies to be made?
o A pairs with T and C pairs with G through hydrogen bonding
o Purine always pairs with pyrimidine due to size
o If one base is know it can only pair with one other base
What does the Meselson and Stahl experiment measure?
o They used test tubes to measure the weight of isotopes of Nitrogen which showed DNA replication in action
o In the first test tube, the heavy DNA N15 was at the bottom
o In test tube 2, the band of DNA was higher, as it was a mixture of N14 and N15
o In test tube 3, there were 2 bands; one with a mixture of N15 and N14 and one with just N14
