Lecture 2- Eukaryotic DNA replication Flashcards
what is the eukaryotic replication phase
S phase
how many replication forks are there in bacterial DNA replication?
2
how many replication forks are there in eukaryotic DNA replication?
can be many- form ‘replication bubbles’
first protein complex which binds to DNA to initiate replication
ORC- origin recognition complex
2nd proteins to bind to the DNA
DNA helicase Mcm2-7
what proteins facilitate helicase loading?
Cdc6, Cdt1
what activates DNA helicase?
CDK and DDK- these lead to the generation of ssDNA which can be replicated by pols
when do polymerases load to DNA?
late G1 phase into S
features of pol alpha
acts as a primase (produces primers), doesn’t do a lot of replicating
pol epsilon and delta- features compared to alpha
better error rates and proofreading activity than pol alpha
which polymerase stays on the strand longest?
epsilon- keeps replicating until it hits another fork as it takes the leading strand
pol delta activity
takes on the lagging strand, so stops and starts more
which proteins join Okazaki fragments?
Fel1 and DNA ligase I
what happens once the helicases reach another primer?
helicase switches to encompass both strands
what triggers the removal of the replication complex from the DNA?
ubiquitilation of Mcm7 (helicase)- but is not broken down- complex removed from chromatin by p97 ATPase
example of how replication origins can be specified
AT rich region in S pombe, epigenetic marks and G4 structures in mammals
why might it be advantageous to lack specific replication sequences?
allows change throughout the lifetime, e.g. during development vs adulthood- may be useful to have more origin points when there is a lot of cell division and specialisation
how does a cell ensure there is no replication in G0
not synthesising the necessary proteins, not activating CDK etc, degrading and inactivating proteins during S phase
example of protein deactivation during S as regulation
geminin deactivates DNA replication factor CDT1, which acts as a ‘licencing factor’ in the ORC. also ubiquitinated and broken down following formation of a replication fork
what is a ‘temporal program’?
different clusters of replication happening at different times throughout S phase
how can we identify temporal programs?
denaturing and staining at a specific point, or looking at shifts from euchromatin to heterochromatin
why might temporal programs exist?
to reduce the energy/dNTP/etc burden on cells, or to alter copy number- more early genes should be replicated than late
