Unit 12- DNA Replication Flashcards
types of replication
- conservative replication
- dispersive replication
- semiconservative replication
Mesel’s and Stahl’s experiment
2 isotopes of nitrogen
- 14N common form; 15N rare, heavy form
- E coli were grown in 15N then to 14N media
- grown E.coli were centrifuged (density gradient)
replicons
units of replication (how long from 1 origin of replication)
theta replication
circular DNA, E. Coli; single origin of replication forming a replication fork, and it is usually bidirectional replication
rolling-circle replication
virus, F factor of E.Coli; single origin of replication (cut one side DNA and synthesize, pealing off strand. peeled off strand loops and is copied)
linear eukaryotic replication
- eukaryotic cells
- thousands of origins
- a typical replicon: ~200000-300000 bp
requirements of eukaryotic replication
- a template strand
- raw material: nucleotides (dNTPs)
- enzymes and other proteins
Direction of replication
- DNA polymerase adds nucleotides only to the 3’ end of growing strand
- replication can only go from 5’ to 3’
(5’ end: phosphate side
3’ end: OH end) - continuous and discontinuous replication
leading strand
undergoes cont replication
lagging strand
undergoes discontinuous replication
okazaki fragments
discontinuously synthesized short DNA fragments forming the lagging strand
indicator protein
binds to origin and seperates strands of DNA to initiate replication
DNA helicase
unwinds DNA at replication fork
single-stranded-binding proteins (SSBPs)
attach to sing-stranded DNA and prevent secondary structures from forming
DNA gyrase (toperasomerase)
moves ahead of replication fork, making and resealing breaks in the double -helical DNA to RELEASE the TORQUE that builds up as a result of unwinding
DNA primase
synthesizes a short RNA PRIMER to provide a 3’-OH group for the attachment of DNA nuclotides (* multiple for lagging)
DNA polymerase III
elongates a new nucleotide strand from the 3’ (moves 3’ to 5’)(new DNA in the 5’ to 3’ direction)
DNA polymerase I
removes RNA primers and replaces them with DNA
DNA ligase
joins okazaki fragments by sealing breaks in sugar-phosphate backbone
*Heteroplasmy
when a cell has mitochondria/chloroplast that have different genes in each
origin-recognition complex (ORC)
binds to replication start site to initiate DNA replication
- recruits and loads helicase
- not needed in Eukaryotes
DNA polymerase delta
lagging-strand synthesis, DNA repair, translesion DNA synthesis
DNA polymerase epsilon
leading-strand synthesis
end-replication problem
end cant be synthesized on lagging strand as Primase doesn’t have enough space to bind and replicate ending
