8Section 11.1The Taylor-Woods-Hughes experiment demonstrated that DNA replication is semiconservative in eukaryotes.
9Semiconservative Replication - http://youtu.be/yyUNaSQf4zs Mechanism of DNA Replication (Basic) -Mechanism of DNA Replication (Advanced) -DNA Replication Process -
10Section 11.1DNA replication begins at the origin of replication and is bidirectional rather than unidirectional.A replicon is the length of DNA that is replicated following one initiation event at a single origin.
11Section 11.2DNA Synthesis in Bacteria Involves Five Polymerases, as well as Other EnzymesDNA polymerase I catalyzes DNA synthesis and requires a DNA template and all four dNTPs.
12Polymerase DirectionChain elongation occurs in the 5' to 3' direction by addition of one nucleotide at a time to the 3' end.
13Section 11.2DNA polymerases I, II, and III can elongate an existing DNA strand (called a primer) but cannot initiate DNA synthesis.All three possess 3' to 5' exonuclease activity.But only DNA polymerase I demonstrates 5' to 3' exonuclease activity.
14Section 11.2DNA polymerase III is the enzyme responsible for the 5' to 3' polymerization essential in vivo.Its 3' to 5' exonuclease activity allows proofreading.
15Section 11.2 Polymerase I is believed to be responsible for: removing the primerthe synthesis that fills gaps produced during synthesis
16Section 11.2DNA polymerases I, II, IV, and V are involved in various aspects of repair of damaged DNA.
17Section 11.2DNA polymerase III has 10 subunits whose functions are shown in Table 11.3.
18Polymerase III Holoenzyme (made of many protein subunits) in E. coli Shevelev, Igor and Hubschur, Ulrich “The 3’ to 5’ exonucleases.” Nature Reviews Molecular Cell Biology 3, pg Retrieved 11/5/13 from
197 key issues that must be resolved during DNA replication: Section 11.3 Many Complex Tasks Must Be Performed during DNA Replication7 key issues that must be resolved during DNA replication:unwinding of the helixreducing increased coiling generated during unwindingsynthesis of a primer for initiationdiscontinuous synthesis of the second strandremoval of the RNA primersjoining of the gap-filling DNA to the adjacent strandproofreading
20Section 11.3 – Unwinding DNA Helix DnaA binds to the origin of replication (oriC) and is responsible for the initial steps in unwinding the helix.
21Section RNA PrimerTo elongate a polynucleotide chain, DNA polymerase III requires a primer with a free 3'-OH group.Enzyme primase synthesizes an RNA primer that provides the free 3'-OH required by DNA polymerase III
22Section 11.3As replication fork moves, only 1 strand can serve as template for continuous DNA synthesis—the leading strand.Opposite lagging strand undergoes discontinuous DNA synthesis.
23Section 11.3Both DNA strands are synthesized concurrently by looping the lagging strand to invert the physical but not biological direction of synthesis.
24Section 11.3Proofreading and error correction are an integral part of DNA replication.All of the DNA polymerases have 3' to 5' exonuclease activity that allows proofreading.
25Section 11.4DNA synthesis at a single replication fork:
26Section 11.6Eukaryotic DNA Synthesis Is Similar to Synthesis in Prokaryotes, but More ComplexIn eukaryotic cells:there is more DNA than prokaryotic cellsthe chromosomes are linearthe DNA is complexed with proteins
27Section 11.6Eukaryotic chromosomes contain multiple origins of replication to allow the genome to be replicated in a few hours.
28Section 11.63 DNA polymerases are involved in replication of nuclear DNA.1 involves mitochondrial DNA replication.Others are involved in repair processes.
29Section 11.6 Pol and d and Ɛ Pol Polymerase switching occurs major forms of the enzyme involved in initiation and elongation.Pol possesses low processivity.functions in synthesis of RNA primers during initiation on the leading and lagging strands.Polymerase switching occursPol is replaced by Pol d and Ɛ, which has high processivity, for elongation.
30Section 11.7Telomeres Provide Structural Integrity at Chromosome Ends but Are Problematic to ReplicateTelomeres at the ends of linear chromosomes consist of long stretches of short repeating sequences and preserve the integrity and stability of chromosomes.
33Section 11.7Lagging strand synthesis at end of chromosome is a problem b/c once the RNA primer is removed, there is no free 3'-hydroxyl group from which to elongate.
34Section 11.7Telomerase directs synthesis of the telomere repeat sequence to fill gap.This enzyme is a ribonucleoprotein w/an RNA that serves as the template for the synthesis of its DNA complement.
35Section 11.8DNA Recombination, Like DNA Replication, Is Directed by Specific EnzymesGenetic recombination involves:endonuclease nickingstrand displacementligationbranch migrationduplex separation to generate the characteristic Holliday structure (chi form)
36Figure Model depicting how genetic recombination can occur as a result of the breakage and rejoining of heterologous DNA strands. Each stage is described in the text. The electron micrograph shows DNA in a -form structure similar to the diagram in (g); the DNA is an extended Holliday structure, derived from the ColE1 plasmid of E. coli. David Dressler, Oxford University, EnglandFigure 11.18
37Section 11.9 Gene Conversion Is a Consequence of DNA Recombination Gene conversion is characterized by nonreciprocal genetic exchange between two closely linked genes.