_4__DNAreplication (2)
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DNA Replication
General Features of Replication
▪The double-stranded DNA run in opposite direction ▪Unwind the helix ▪Intrastrand annealing ▪A number of enzymes involved ▪Replication errors ▪Higher structures of DNA add complexity ▪Origins and terminus
5’
Lagging Leading
5’ strand strand
3’
3’ 5’ 3’
Unidirectional and bidirectional replications
Bidirectional replication of a circular bacterial DNA
❖replicon: unit of the genome which is replicated
5’
Lagging Leading
5’ strand strand
3’
3’ 5’ 3’
Semiconservative Replication
Each of the parental duplex is a template for DNA replication.Each of the two daughter duplexes consists of one parental strand and one newly synthesized strand.
❖ DNA topoisomerase II
Unwind highly coiled DNA
Helicase: break the hydrogen bond and eliminate hydrophobic interactions. The separated strands are inhibited from subsequently reannealing by a single-strand-binding protein (SSB protein), which binds to both separated strands.
❖ The E. coli replication origin oriC is an ≈240-bp DNA segment ❖ A conserved repetitive 9-bp and AT-rich 13-bp sequences,
referred to as 9-mers (dnaA boxes) and 13-mers, respectively . ❖ Plasmids or any other circular DNA containing oriC are capable
Origin
Daughter DNA
Terminus structure
Multiple eukaryotic replicons
Байду номын сангаас
Unwind highly
coiled DNA
Topoisomerase
A DNA topoisomerase can be viewed as a reversible nuclease that adds itself covalently to a DNA phosphate, thereby breaking a phosphodiester bond in a DNA strand. Because the covalent linkage that joins a topoisomerase to a DNA phosphate retains the energy of the cleaved phosphodiester bond, the cleavage reaction is reversible; resealing is rapid and does not require additional energy input.
Initiation of DNA Replication
Replication starts at specific base sequence, known as ‘origin of replication’ (ori). De novo initiation fig 7.6
E. coli Replication Origin
❖A replicon contains:an origin of replication.
❖E. coli: contains a single origin of replication
❖Mouse: contains 25,000 replicons, ≈150 kb each; distributed between multiple linear chromosomes
SV40 Replication
Origin
❖ The SV40 origin of replication is adjacent to the viral transcription control region. Initiation of replication depends on the viral large T antigen, which binds to a region within the 64 bp ori core including several essential elements[1: four pentamers (5’GAGGC3’ );2: a 15bp palindrome; 3: a 17 bp region consisting only of A-T pair]
of independent and controlled replication in E. coli cells.
Yeast Autonomously Replicating Sequences
❖ A conserved essential element, a 15-bp segment, designated element A, stretching from position 114 through 128.
❖ Three other short segments — the B1, B2, and B3 elements — increase the efficiency of ARS1 functioning.
Sequences of bacterial and yeast
replication origins:
General Features of Replication
▪The double-stranded DNA run in opposite direction ▪Unwind the helix ▪Intrastrand annealing ▪A number of enzymes involved ▪Replication errors ▪Higher structures of DNA add complexity ▪Origins and terminus
5’
Lagging Leading
5’ strand strand
3’
3’ 5’ 3’
Unidirectional and bidirectional replications
Bidirectional replication of a circular bacterial DNA
❖replicon: unit of the genome which is replicated
5’
Lagging Leading
5’ strand strand
3’
3’ 5’ 3’
Semiconservative Replication
Each of the parental duplex is a template for DNA replication.Each of the two daughter duplexes consists of one parental strand and one newly synthesized strand.
❖ DNA topoisomerase II
Unwind highly coiled DNA
Helicase: break the hydrogen bond and eliminate hydrophobic interactions. The separated strands are inhibited from subsequently reannealing by a single-strand-binding protein (SSB protein), which binds to both separated strands.
❖ The E. coli replication origin oriC is an ≈240-bp DNA segment ❖ A conserved repetitive 9-bp and AT-rich 13-bp sequences,
referred to as 9-mers (dnaA boxes) and 13-mers, respectively . ❖ Plasmids or any other circular DNA containing oriC are capable
Origin
Daughter DNA
Terminus structure
Multiple eukaryotic replicons
Байду номын сангаас
Unwind highly
coiled DNA
Topoisomerase
A DNA topoisomerase can be viewed as a reversible nuclease that adds itself covalently to a DNA phosphate, thereby breaking a phosphodiester bond in a DNA strand. Because the covalent linkage that joins a topoisomerase to a DNA phosphate retains the energy of the cleaved phosphodiester bond, the cleavage reaction is reversible; resealing is rapid and does not require additional energy input.
Initiation of DNA Replication
Replication starts at specific base sequence, known as ‘origin of replication’ (ori). De novo initiation fig 7.6
E. coli Replication Origin
❖A replicon contains:an origin of replication.
❖E. coli: contains a single origin of replication
❖Mouse: contains 25,000 replicons, ≈150 kb each; distributed between multiple linear chromosomes
SV40 Replication
Origin
❖ The SV40 origin of replication is adjacent to the viral transcription control region. Initiation of replication depends on the viral large T antigen, which binds to a region within the 64 bp ori core including several essential elements[1: four pentamers (5’GAGGC3’ );2: a 15bp palindrome; 3: a 17 bp region consisting only of A-T pair]
of independent and controlled replication in E. coli cells.
Yeast Autonomously Replicating Sequences
❖ A conserved essential element, a 15-bp segment, designated element A, stretching from position 114 through 128.
❖ Three other short segments — the B1, B2, and B3 elements — increase the efficiency of ARS1 functioning.
Sequences of bacterial and yeast
replication origins: