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Bacterial plasmids by E. Börje Lindström Definitions • Replicon: - a DNA-molecule with its own replication • Plasmid: - a small extra-chromosomal replicon (autonomous) - DS, closed molecule - 1 – 1000 bp • Episome: -a plasmid that can be integrated into the chromosome - e.g. the F-plasmid • Transposon: - a movable genetic element Different plasmids Grouped after their properties: • F-plasmid /factor: 100 kb Different plasmids, cont. • R- plasmid: - have genes for resistance against antibiotics and/or heavy metals Size in kb pairs Plasmid R100 Different plasmids, cont. • Col – plasmids: - produces colicins - antibacterial • Catabolic plasmids: -have properties to use odd carbon/ energy sources - many Psuedomonas have such plasmids • Cryptic plasmids: - no known property Plasmid genes Grouping 1) Essential genes for keeping the plasmid within the cell • Replication: -uses the replication system of the host cell - have its own initiation, elongation and termination - occurs during the entire cell cycle •Copy number: -a certain amount of copies present per cell - controlled by the initiation frequency - low (1-4) to high (10-100) Plasmid genes, cont. • Partitioning: • Host specificity/range: - only a problem for low and medium copy number - low to broad 2) Non-essential –important for transfer • Are spread horizontally (among bacteria) • Important genes - pili-genes - oriT - tra/ mob genes Plasmid genes, cont. 3) Non-essential –with surviving value • Resistance against antibiotics • Production of antibacterial substances (colicins) • genes for pathogenesis/virulence • genes to be able to use special energy/carbon sources, e.g. phenol