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Mechanism of bacterial DNA replication, 3.Separation of catenanes - Coggle…
Mechanism of bacterial DNA replication
initiation of replication
Histone protein binds to the origin of the replication while helicase unbinds the DNA helix
to produce two replication forks from the origin
Topoisomerase is a protein that binds to the double helix ahead of the replication fork and relieves the strained placed on the double helix as it unravels
single-strain binding protein (SSBs) prevents the separated starins from joining together again by binding to them and stabilizing them
dna strand separation and rna primer
The separated strands of DNA act as a template
it separated by the
DNA helicase enzyme
DNA gyrase (topoisomerase)
travels ahead of the helicase and alleviates supercoiling
Single-stranded binding proteins
prevent the single-stranded DNA from reannealing
A small RNA primer is synthesized by
DNA primase.
-In the leading strand, a single primer is made at the origin of replication
-In the lagging strand, multiple primer are made.
Okazaki fragments
newly synthesized DNA fragments that are formed on the lagging template strand during DNA replication
They are complementary to the
lagging template strand, together forming short double-stranded DNA sections.
Okazaki fragments
between 1,000 and
2,000 nucleotides long in
Escherichia coli
between 100-200
nucleotides long in
eukaryotes
They are separated by ~10- nucleotide RNA primers and are unligated until RNA primers are removed
followed by
enzyme ligase
then, connecting (ligating) the two Okazaki fragments into one continuous newly synthesized complementary strand
Protein involved in E. coli DNA replication :
DnaA protein
Binds to DnaA boxes within the origin to initiate DNA replication
DnaC protein
Aids DnaA in the recruitment of DNA helicase to the origin
DNA helicase (DnaB)
Separates double-stranded DNA
Topoisomerase/DNA gyrase
Removes positive supercoiling ahead of the replication fork
Single-strand binding protein
Binds to single-stranded DNA and prevents it from reforming a double-stranded structure
Primase
Synthesizes short RNA primers
DNA polymerase III
Synthesizes DNA in the leading and lagging strands
DNA polymerase I
Removes RNA primers, fills in gaps with DNA
DNA ligase
Covalently attaches adjacent Okazaki fragments
DNA polymerase
DNA polymerase III
conducts most of the DNA replication
a large enzyme consists of 10 different subunits that play various roles in the DNA replication process
combined the structure is called a DNA polymerase III holoenzyme
In leading strand synthesis, it will attaches nucleotides as it moves in a 5’ to 3’ direction
In lagging strand, the replication occurs away from the replication fork and still in the 5’ to 3’ direction
synthesizing the DNA of
the leading and lagging strands
catalyzes the formation of covalent bonds
between adjacent nucleotides
makes the new daughter
strands
There are five polymerases which is I, II, III, IV, V
DNA polymerase I
removes the RNA primer
mainly to support repair of damaged DNA
replacing the ribonucleotides with DNA
dna polymerase ||| as a processive enzyme
1.The enzymatic action of DNA
polymerase
deoxyribonucleoside triphosphate (dNTP) cleaved to form nucleoside monophosphate and pyrophosphate (PPi).
energy released from the exergonic reaction allow the nucleoside monophosphate to form covalent bond at 3’ end of the growing strand.
this reaction catalyzed by
DNA polymerase
.
PPi
is released.
2.The termination of DNA replication
A pair of termination sequences
(ter)
The T1 ter sequence prevents
clockwise moving forks.
The T2 ter sequence prevents counter-clockwise (right to left) moving forks.
The termination utilization
substrate (Tus)
protein binds to the
termination sequences and prevents the movement of the replication forks.
dna replication complexes
The replication of double-stranded DNA involves a series of
proteins called a replisome.
The combination of the DNA helicase and primase is called a
primosome.
The primosome associates with two DNA polymerase
holoenzymes to form the replisome
Two DNA polymerases that are moving together within a
replication fork are called a dimeric DNA polymerase
A three-dimensional view of DNA replication
DNA helicase + primase= primosome: leads the way at the replication fork.
Primosome + two DNA polymerase holoenzymes= replisome
3.Separation of catenanes
After DNA replication is
completed, the circular DNA may form interlinked loops,called
catenanes
.
