Chapter 12 - The replicon: Initiation of Replication Flashcards
(40 cards)
A replicated region appears as
A replication bubble within nonreplicated DNA.
Replication is initiated at
A specific sequence/region called the Origin.
Replicon
The DNA that is duplicated with initiation of
replication at the origin.
Replication unit(s) on a prokaryotic cell
One replicon
Replication unit(s) on a eukaryotic cell
Multiple replicons
Each replicon is activated at a specific time during the S-phase of the cell cycle (difficult to characterize individual replicons).
Multiple origins of replication ultimately merge during replication.
No termination or ter site required.
Number of replication initiation events that occur for every cell division in prokaryotes or eukaryotes
A single replication initiation event occurs at the origin
once for every cell division.
In eukaryotes what is duplicated during Gap 1 (G1)
RNA, protein, lipids, carbs, etc.
In eukaryotes what is duplicated during Synthesis (S)
DNA ONLY
Where is/are the checkpoint(s) for damaged DNA
End of Gap 1, end of Gap 2
Where is/are the checkpoint(s) for chromosome misalignment
End of M
Single replication fork
Replication is unidirectional when a single replication fork is created at an origin.
Two replication forks
Replication is bidirectional when an origin creates two replication forks that move in opposite directions. Most prokaryotes and eukaryotes use bidirectional replication.
θ structure
In bacteria, the replication bubbles forms the θ structure.
No θ structure in eukaryotes because replication occurs on linear DNA, but eukaryotes do exhibit a replication bubble.
What happens if replicating chromosomes become catenated?
Chromosomes require segregation.
The origin of E. coli
OriC. 245 bp in length.
Contains:
1. Binding sites for the replication initiating protein DnaA.
2. 11 GATC/CTAG palindromic sequences.
3. The Adenine in the sequence is methylated by the Dam
methylase enzyme.
What is the Xer site-specific recombination system?
Includes:
2 Recombinases: XerC and XerD
The dif gene sequence near the replication termination region.
Recombinases bind to the dif site and form Holliday junction.
FtsK, which resolves the junction, is located at the septum.
Replication termination region associates with septum; hence movement of the dif site +/- 30 kb, inhibits recombination event.
Where are a majority of genes transcribed?
Leading strand.
What happens when the replication fork encounters a DNA-bound protein or transcription machinery in the SAME direction?
The replication fork can slow down and wait for RNAP to reach transcription termination.
-OR-
Replication fork can bypass the RNAP through unknown mechanisms.
What happens when the replication fork encounters a DNA-bound protein or transcription machinery in the OPPOSITE direction?
Both processes are halted and RNAP is displaced.
Dam methylase
Converts hemimethylated DNA to full methylated strands. Releases SeqA from the origin.
Methylates the Adenine in the GATC/CTAG palindromic sequence.
DnaA
Replication initiating protein.
The licensing factor (necessary for replication; destroyed after one round of replication).
Active only when bound to ATP.
ATPase activity hydrolyzes ATP to ADP.
Functions to melt DNA.
Binding sites include 13- and 9-mers repeats.
At the initiation of replication is the palindromic sequence methylated on one or both strands?
Both strands.
In E. Coli does replication generate hemimethylated or fully methylated DNA?
Hemimethylated - cannot initiate replication.
SeqA
Binds hemimethylated DNA; delays re-replication by sequestration.
A sequestration factor. Inhibits DnaA binding.