MCB 2610 Chapter Notes - Chapter 7: Dna Repair, Dna Mismatch Repair, Dna Replication
25 May 2018
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The start of replication is controlled by the protein DnaA:
● It recognizes oriC and melts it so that replication enzyme can load
● It also acts as a timer to control when replication starts
● Therefore it controls WHEN and WHERE replication starts.
Fidelity of DNA replication:
● During replication of DNA in E.coli, a permanent mistake is made once in every 10 bp
base pairs (error rate is said to be 10^-10 per bp)
Contributions to decreased error rates:
● The DNA polymerase reaction itself has an error rate of 1 mistake per 1000 bp
● Proof reading (3’->5’ exonuclease nuclease activities) reduces that:
Done by PolIII subunit DnaQ
A PolI domain dedicated to proofreading
These contribute ~ 100 fold decrease in error rates
A process called methyl directed mismatch repair contribtues to a ~1000 fold further decrease in
error rates
Total of proof reading + MDMR is ~10^5 fold. Enough to bring PolIII error rate to the overall of
~10. Other systems are in place to deal with various types of DNA damage (SOS repair,
excision repair, photoreactivation, etc,..)
Chromosome (genome) organization:
● Circular
● Linear
● Large plasmids
Chromosome partitioning
Geometry of chromosome partitioning
Sister of chromosome cohesion model: Newly synthesized chromosomes stay together and
are separated late in the cell division cycle
Extrusion capture model: Chromosomes are partitioned into separate sides of the cell as they
are synthesized
Partitioning machinery:
This is still a wide open area of research, but it is becoming clear that there are several ways to
do this. Most of the molecular work has been done using plasmids
Antibiotics that affect DNA synthesis:
Know: Trimethoprim
Dideoxynucleotides
Ethidium
Nalidixic acid
Document Summary
The start of replication is controlled by the protein dnaa: It recognizes oric and melts it so that replication enzyme can load. It also acts as a timer to control when replication starts. Therefore it controls when and where replication starts. During replication of dna in e. coli, a permanent mistake is made once in every 10 bp base pairs (error rate is said to be 10^-10 per bp) The dna polymerase reaction itself has an error rate of 1 mistake per 1000 bp. Proof reading (3"->5" exonuclease nuclease activities) reduces that: These contribute ~ 100 fold decrease in error rates. A process called methyl directed mismatch repair contribtues to a ~1000 fold further decrease in error rates. Total of proof reading + mdmr is ~10^5 fold. Enough to bring poliii error rate to the overall of. Other systems are in place to deal with various types of dna damage (sos repair, excision repair, photoreactivation, etc,)
