Ch 10 Lecture (Replicon) Flashcards
replicon
A unit of the genome in which an individual act of replication occurs
Each contains an origin for initiation of replication
origin of replication
Physical site on DNA where DNA is unwound and replication is initiated
replicator
Cis-acting DNA sequences sufficient to direct the initiation of DNA replication
Origin is always part of replicator, but is often only a portion of it
terminus
A segment of DNA at which replication ends
bacterial chromosomes each contain how many origins of replication
one
Eukaryotic chromosomes contain a large number of c
unevenly spaced replicons
how many times are replicons fired during eukaryotic replication
once
semiconservative replication
Both strands of a parental duplex are separated
Each strand then acts as a template for synthesis of a complementary strand
replication fork
Point at which replication occurs
Initiated at the origin and then moves sequentially along the parental duplex
replication bubble
How a replicated region appears within unreplicated DNA when viewed by electron microscopy
Appearance does not distinguish between unidirectional and bidirectional replication
bacterial chromosomes are usually
circles that replicate bidirectionally from a single origin
the early stage of bacterial replication is sometimes called
a theta structure
oriC
The replication origin of E. coli
245 bp in size
DnaA
Bacterial replication initiator protein
Binds to DnaA boxes in oriC
Binding of DnaA to oriC is influenced by
interactions with ATP and ADP
OriC contains how many copies of the palindromic sequence GATC
11
The adenine in this palindrome is a target for methylation by
Dam methylase enzymes
where are dam methylation sites located
Dam methylation sites are scattered throughout the genome, but several overlap DnaA boxes
what does Dam do before replication begins
the adenines of the palindromic sequence are methylated on both parental strands by Dam
after replication, the DNA is considered
hemimethylated
hemimethylated origins
inhibit initiation of replication
only fully methylated origins can
initiate replication
The GATC sequences at hemimethylated oriC remain
hemimethylated following replication much longer than GATC elsewhere in genome
Hemimethylated promoter inhibits expression of
DnaA protein
therefore delays re-initiation of replication