CHAPTER 34: DNA ReplicationProblems 1-6, 9-10,12,17
Genetic information Archive Blueprint Copying
Transcription TranslationBioinformatics
Metabolic networks Regulatory networks Systems Biology
34.1: DNA Replication Polymerases
“Throughout college I worked evenings, weekends, and school holidays as a salesman in men’s furnishings stores. This left little time for study or sleep and none for leisure. With these earnings, a New York State Regents Scholarship of $100 a year, no college tuition, and frugal living, I saved enough to see myself through the first half of medical school at the University of Rochester.”Arthur Kornberg, from his book “Never a Dull Enzyme”.
Arthur Kornberg (1918‐2007) Nobel Prize 1959.
DNA Pol I Klenow fragment:5’→3’ polymerase activity3’→5’ exonuclease activity
The 5’→3’- exonuclease activity is present in another portion of the Pol I protein not shown here.
DNA Polymerization occurs with high fidelity due to specificity and error correction
Induced Fit
3’→5’ Exonuclease Proofreading
Pol III: Polymerase error = 10-5, nuclease error 10-2; Overall error rate = 10-7
DNA Replication Requires Unwinding
Helicase
Topoisomerase
Type I topoisomerase: relax supercoiled DNA.Type II topisomerase (gyrase): add negative supercoils to DNA (requires ATP).
Gyrase inhibitors
34.2: DNA Replication is Highly Coordinated
An Origin for DNA Replication
A helicase
• Replication involves initiation, elongation, and termination.
• E. coli chromosome is circular, double-stranded DNA (4.6x103 kilobase pairs, >1000 bp/sec)
• Replication begins at a unique site (origin)• Proceeds bidirectionally until the two replication
complexes meet (termination site)• Replisome - protein machinery for replication
(one replisome at each of 2 replication forks)
DNA Replication Requires a Primer, is Both Continuous and Discontinuous, Processive, and Coordinated.