L11 - DNA replication 3 Flashcards
diferences in replication orogins between eukaryotes and prokaryotes
eukaryotes have multiple wheras prokaryotes have 1
orgogins = where unwinding occurs for DNA replication to take place
= replisome forms here
only a few orogins of replication in eukayotes will be fired
what can happen if timing of DNA replication is off/wrong
double strand breaks
= poor timing can leave unreplicated regions of DNA
motors that pull apart chromosones at kinetichores are very powerful
when chromosomes try to seprate in DNA replication
= unreplicated regions cannot seperate = ds BREAK
what controls the timng of firing at replication of orgins for DNA replication
CDKs
= cyclin dependnat kinases
describe the mechnaisms for the initiation of replication in G1 phase
- ORC binds to replicator sequnce in orogin with cdc26
= Orogin repcognition complex
- recruits Mcm helicase with cdt1
- same thing happens with a 2nd helicase binding
- everything but helicase discoaites leaving just the 2x helicases
= G1 phase
descibe the mechansims of initiation in S phase -
CDKs increase in conc as it enters S phase
= DDK + S-CDK
- DDK phosphprylate helicases = comformational change
- sld3 + cdc45 recruited
- S-CDK phosphorylates changing comformation AGAIN
= more proteins recruited
- comformational change to helicase causes them to open allowing ssDNA to bind
= polymerase binds
describe how the comformation of helicaes + CDKs affects the timing of replication initiation
Helicases can be loaded in G1 phase
BUT no helicase activation as CDK levels are low
G2,S and M phases = CDK leveles are high BUT new helicase laoding is inhibited
= prevents refiring of sites of orogin
names for G1 and S,G2 , M phases in replicaction initiation
G1 = loading phase
S,G2 and M = activation phase
what is the problem with finisng replication on lagging strand
RNA primers are removed to be filled with DNA
the final RNA primer is removed and there is nothing to add on to the 5’ end of the last nucleotide in strand
= the end of the chromosones are lost on 1 strand
= following replication again the ends of both strands will not have the ends
role of telomeres
repeated sequnces of DNA to end of chromosomes
- telomerase extends 3’ end of telomere
- strand is longer so ocazaki fragments go for longer
= still lose the end of chromosome due to RNA primer being removed and nothing to add to it
= lose a non-coding seuqnce instead of a coding sequnce
deosnt solve the problem just delays it
how does telomerase work/extend the 3’ strand
contains stuctured RNA wutha template
binds to complimnetary DNA via base pairng at end of chromosome
the RNA template in telomerase is longer than the complimnetary strand
= polymerase adds nucleotides to the 3’ end
= complimentary to the RNA sequence in telomerase
telomerase has to move along the DNA to continue to act as template
what can double stranded breaks cause
cell cycle arrest
what protein coats and protects telomeres sequnces from repair machinerya
shelterin proteins
= binds to the ssDNA 3’ strand that was extended by telomerase
= hides from cell repair
what happenes if telomeres get too short
cell can no longer divide
= would start to remove coding regions
= known as ‘Hayflick limit’
what controls the loadiung of the 2 DNA helicases at the orgin
‘ATPase switches’
= ORC for example
