DNA. replication Flashcards
How is DNA is seperated? Why does it happen?
In order for DNA to replicate the double helix structure has to unwind and separate into two strands, so the hydrogen bonds holding the complementary bases together must be broken.
DNA helicase unwinds the DNA #
exposes the bases
How is the strand replicated
Free DNA nucleotides will then pair up with their complementary bases, which have been exposed as the strands separate.
Hydrogen bonds are formed between them and finally the new nucleotides join together to their adjacent nucleotides with phosphodiester bonds
enzyme is is DNA polymerase
How is this semi-conservative replication?
two new DNA molecules are produced
each one consists of one old strand of DNA and one new strand
What is the 3’ end and the 5’ end?
3’ prime is when the DNA chain ends with the an unjoined third carbon (bottom left on the ribose sugar), this attaches to the phosphate group of anoher molecule
5’ prime end is when the chain ends with an unjoined carbon 5’ (which attaches to the phosphate group
What is significant about the different ends?
DNA polymerase always moves along the template strand (DNA strand the is being transcribed) from the OH group on the carbon-3 (3’) so travels in the direction of 3’ to 5’
What does it mean that the strands run anti-parallel? What is the significance of this during replication?
One strand ends with 5’ and the other with 3’
as DNA can only unwind and unzip in one direction, DNA polymerase has to replicate each of the template strands in opposite direction
Which strand is translated continuously? What is the meaning of this?
3’ end strand is replicated continously (DNA polymerase always moves from the 3’ primer end)
this is called the leading strand
DNA polymerase moves along the 3’ strand
What is the replication fork?
DNA chain is split and forms a replication fork, due to DNA helicase, (held apart by proteins so DNA polymerase can replicate the DNA)
What strand is replicated discontinuously?
strand unzipped from the 5’ end so DNA polymerase can can only work along the strand after waiting for DNA helicase to unzip the strand
results in the DNA being produced in Okozaki fragments which have to be joined together by DNA ligase
this occurs at multiple point along a chromosome
