The Genetics of Bacteria

Bacterial Chromosome Circular, double-stranded DNA molecule tightly condensed into a structure called a nucleoid, which has no nuclear membrane Bacteria replicate their DNA in both directions from a single point of origin This is called theta replication, since the process resembles the Greek letter Θ

Bacterial Reproduction Binary fission Asexual Results in a population with identical genes Mutations DO occur spontaneously Mutations are rare, and 1 in 1,000 can significantly change the population as a whole Conjugation Primitive sexual method Transfer of genetic material between bacteria by direct cell-to-cell contact

Bacterial Transformation Discovered by Frederick Griffith after using Diplococcus pneuomoniae Can be natural or artificial Provides a mechanism for recombination of genetic information in some bacteria

Bacterial Transformation Small pieces of extracellular DNA are taken up by a living bacterium, leading to a stable change in the recipient cell Common for people with insulin deficiencies (diabetes)

Plasmid A foreign, small, circular, self-replicating DNA molecule that inhabits a bacterium Bacteria can harbor many plasmids and will express the genes carried by the plasmid The first plasmid discovered was the F plasmid, in which F stands for fertility

F Plasmid Bacteria that do not contain the F plasmid are called F- Bacteria that contain the F plasmid are called F+ Bacteria that do not contain the F plasmid are called F- The F plasmid contains genes that produce pili, cytoplasmic bridges that connect to an adjacent cell and that allow DNA to move from one cell to another in a form of primitive sexual reproduction called conjugation

R Plasmid Makes the cell in which it is carried resistant to specific antibiotics Can be transferred to other bacteria by conjugation Bacteria with the R plasmid have a distinct evolutionary advantage over bacteria that are not resistant to antibiotics This is happening today, particularly with tuberculosis