Lec 2 Chapter+11+the+replicon-2011-b1

Lec 2 Chapter+11+the+replicon-2011-b1 - Chapter 11 The...

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Unformatted text preview: Chapter 11 The Replicon Replicon : a unit of DNA in which individual acts of replication occur; contains an origin (replication start) and may have a terminus .- occurs once for every cell Chapter 11: THE REPLICON E. Coli chromosome Is a single replicon. Bacteria*, plasmids Bacteriophage & Phage have single replicons (*bacterial chromosome ) From Microbial Genetics, (1987) D. Friefelder, Jones & Bartlett, 601 pp. (ONE Ori of REPLICATION) However, some Archae have multiple origins. Plasmid : autonomous circular DNA genome that constitutes a separate replicon. single copy control- replicates once alongside bacterial chromosome. multicopy control- How many origins of replication in a plant cell? Nucleus? Chloroplasts? Mitochondria? Nu Chl Nu Mit Chl From: Arabidopsis An Atlas of Morphology and Development , J. Bowman (ed.)1994. Springer-Verlag, New York. 450 pp. General rules for replication: 1. Initiation of DNA replication commits cells to division . 2. Division must not occur until after replication is completed. Note : Replication is controlled at the stage of initiation. Types of replication control: 1. Single copy : bacterial chromosome, some plasmids, eukaryotic chromosomes. note : Eukaryotic chromosomes have many replicons; control is a problem; all must activate once in cell cycle, but no more. II. Origins can be mapped by electron microscopy, autoradiography & gel electrophoresis. 1. replication fork: point at which replication is occurring (growing point). 2. may be unidirectional 3. or bidirectional. bacterial and eukaryotic chromosomes replication eye Ori Ori I. Replicons can be linear or circular A replication fork: is initiated at the origin moves sequentially along DNA Replication is unidirectional when a single replication fork is created at an origin. Replication is bidirectional when an origin creates two replication forks that move in opposite directions. Figure 11.3 Appears under EM as structure. structure Replication eye forms a theta structure in circular DNA two daughter duplexes replicating ColE1 plasmid DNA from E. coli Is replication unidirectional or bidirectional? 1 3 2 4 5 6 7 8 unidirectional.-only one end moves Origins Can Be Mapped by Autoradiography, Fluorescent Labeling and Electrophoresis Replication fork movement can be detected by autoradiography using radioactive pulses. Drosophila DNA replication studied using differential labeling heavy light light Bidirectional replication FIGURE 06_TOP: Initial replication is detected by incorporation of green label Photo reproduced from K. Marheineke, et al., Visualization of bidirectional initiation of chromosomal DNA replication in a human cell free system, Nucleic Acids Res., vol. 33 (21), pp. 6931-3941, by permission of Oxford University Press. Photo courtesy of Kathrin Marheineke and Torsten Krude....
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Lec 2 Chapter+11+the+replicon-2011-b1 - Chapter 11 The...

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