6. DNA replication 2 Flashcards
what is the function of DNA pol 1?
DNA repair and primer removal
what is the function of DNA pol 2?
DNA repair
what is the function of DNA pol 3?
DNA synthesis for replication
what are the requirements replication must have in E Coli? 4 points
Ecoli is a single circular chrmosome of double stranded DNA.
- no breaks in strands
- strands have opposite polarity
- semi conservative replication
- cell division is every 20 mins
how was E coli studied to understand the process of DNA replication in Ecoli?
radioactive labelling of H-thymidine
are both sides of the replication fork moving during replication? explain
yes, replication is bidirectional meaning the replication begins at the origin of replication and moves around the circle to the replication fork
where does replication begin on Ecoli?
on a gene called OriC which is the origin of replication. its a gene that dosent code for a protein and means replication always occurs on the same spot
how does DNA replication get past the problem on that DNA pol can only synthesis in the 3’-5’ direction?
there is semicontinuous replication.
the leading strand is continuous, the lagging strand has okazaki fragments which replicate backwards
how does replication begin on each okazaki fragment?
RNA primase (type of RNA polymerase) is synthesised which is used as a primer to begin DNA replication for DNA polymerase
how is the primer removed after replication?
removed by the 5’ exonucelase activity of DNA polymerase 1
(DNA polymerase 3 is whats doing all the replication)
how are the lagging strands joined?
with the enzyme ligase
joins DNA framents with 5’-phosphate and 3’OH
