DNA replication Flashcards
semiconservative model:
parent DNA unwinds, and 2 new daughter strands have og one strand
list 6 proteins involved in DNA replication
- helicase
- topoisomerase
- primase
- DNA polymerase
- single strand binding (SSB)
- DNA ligase
topoisomerase:
breaks, rejoins and swivels DNA
helicase:
untwist and separates DNA helix
primase:
sythesises RNA primers
DNA polymerase:
synthesises new DNA strand
SSB:
single strand binding bind to single DNA strands and keep them from rejoining
DNA ligase:
joins pieces of DNA together (forms phosphodiester bonds)
how does replication begin:
at origins of replication, 2 DNA strands separated opening replication bubble
which direction does the replication occur?
both directions of each origin
list stages of DNA replication
initiation
elongation
termination
initiation stage:
specific DNA sequence where helix is unwound/ open to enzymes
- helicase unwinds DNA strand
elongation stage:
DNA polymerase add nucleotides to growing DNA strand
termination stage:
end point of replication (where replication forks meet)
replication fork is:
where the end of the bubble has the 2 new growing strands of DNA
how does the leading strand replicate:
- DNA pol III starts synthesising
- continuous elongation from 5’ to 3’ direction
- ATTACHES to 3’ end of strand
how does lagging strand replicate:
- primase makes RNA primer
- DNA pol III makes Okazaki fragment
- from 3’ to 5’ direction
- DNA pol detaches, next fragment primed and is replaces with DNA pol
- DNA ligase forms bonds btw fragments
RNA primer:
short strand of RNA which enables binding of DNA pol, 5-10 nucleotides long
leading strand:
synthesised in SAME direction of growing replication fork
lagging strand:
synthesises AWAY from replication fork
telomeres:
as linear DNA shortens after each replication, these are repeated sequences at end of chromosomes
TTAGGG repeated 100-1000 times in humans
telomerase:
helps maintain length of telomeres
define mutations:
changes in genetic material of cell
- source of new genes
- raw material of evolution/ natural selection
- could be positive, negative (deleterious) or neutral
cause of mutations:
- errors in DNA replication
mutagens:
- from physical agents (xray, UV)
- chemical (tobacco, asbestos)
protein helps cut out incorrect nucleotide: and mechanism
nuclease
nucleotide excision repair
thymine dimers:
caused by UV light, extra bond inhibits normal DNA replication
nuclease - DNA pol - DNA ligase
