Chromosome bacterial

FIGURE 11.22 If the cell walls of bacteria such as Escherichia coli are partially digested and the cells are then osmotlcally shocked by dilution with water, the contents of the cells are extruded to the exterior. In electron micrographs, the most obvious extruded component is the bacterial chromosome, shown here surrounding the cell. (Dr. Gopal Murti/CNRI/Phototakr NYC)... 

The eytoplasm is a viscous fluid and contains within it systems of paramount importance. These are the nucleus, responsible for the genehc make-up of the cell, and the ribosomes, whieh are the site of protein synthesis, hi addihon are found granules of reserve material suehas polylydioxybutyric add, an energy reserve, and polyphosphate or volutin granules, the exact funchon of which has not yet been elucidated. The prokaiyohc nueleus or bacterial chromosome exists in the cytoplasm in the form of a loop and is not surrounded by a nuclear membrane. Bacteria cany other chromosomal elements episomes, which are portions of the main chromosome that have become isolated firm it, and plasmids, whieh may be called miniature chromosomes. These are small annular pieees of DNA whieh carry a limited amount of genetic information. 

Plasmids may be defined as fragments of DNA that replicate outside the bacterial chromosome and they are important in a number of different contexts ... 

Lica LM, Narayanswami S, Hamkalo BA 1986 Mouse satellite DNA, centromere structure, and sister chromatid pairing. J Cell Biol 103 1145-1151 Lin DC, Grossman AD 1998 Identification and characterization of a bacterial chromosome partitioning site. Cell 92 675-685... 

Analogues of the umuDC genes can be found in locations other than the bacterial chromosome, for example, plasmid pKMIOl (Walker and Dobson, 1979), a derivative of the drug resistance plasmid R46 (Mortelmans and Stocker, 1979), which carried mucAB genes (Shanabruch and Walker, 1980) (see pp. 879-880). 

Another viral chromosome that can be used as a vector is that of the filamentous phage Ml3. The M13 chromosome is a single-stranded DNA molecule which when inserted into the bacterial host replicates outside the bacterial chromosome in the cytoplasm. The virus is then reassembled and released from the bacterial cell without cell lysis. 

The bacterial chromosome is a closed, double-stranded circular DNA molecule having a single origin of replication. Separation of the two parental strands of DNA creates two replication forks that move away from each other in opposite directions around the circle. Replicatioii is,... 

E. R C. Rocha, P. Guerdoux-Jamet, I. Moszer, A. Viari, and A. Danchin, Implication of gene distribution in the bacterial chromosome for the bacterial cell factory. J. Biotech. 78, 209-219 (2000). 

The continued evolution of the class is exemplified by the recent report of the ability of a variant of AAC(6 )-Ib, AAC(6 )-Ib-cr, to modify the synthetic fluoroquinolone antibiotic ciprofloxacin (Scheme 3.2.). ° Substrate plasticity may be a general hallmark of the GNAT class and this could help to explain the plethora of these genes in clinical strains and in bacterial chromosomes alike. 

DNA replication begins with protein binding to the origin of replication, a unique sequence in the bacterial chromosome, causing a short region of double-stranded DNA (dsDNA) to unwind (Figure 11-2). 

During the amplification cycles of the PCR, the Taq DNA polymerase copies the DNA between the primers. Because numerous areas throughout the bacterial chromosome are amplified, many potential genetic differences can be detected. Figure D.4 shows a chip analysis of two samples of bacterial DNA amplified by rep-PCR. The gel electrophoresis results clearly show that the bacteria samples are different strains, as there are band differences appearing at approximately... 

Antibiotic resistance in bacteria is not a fixed property, and the degree of resistance detectable in the laboratory probably bears litde relationship to the resistance of the organism when growing in the intestinal tract of animals. The types of resistance that bacteria may develop to the action of antibiotics involve two distinct mechanisms mutation and inheritance. The former mechanism affects DNA sequence and results in the synthesis of a protein or macromolecule by the bacterial chromosome that differs from the original chemical entity, with the ability to interfere with the antibiotic activity. Because an antibiotic hinders a bacterium only after it has entered or crossed the cell wall and has bound to a target site, resistance can develop directly if the mutation has so altered the characteristics of the protein or macromolecule that the cell wall, receptor site, or transport mechanism is no longer friendly to the antibiotic. 

We now turn briefly to the structure of bacterial chromosomes. Bacterial DNA is compacted in a structure called the nucleoid, which can occupy a significant... 

Bacterial chromosomes are also extensively compacted into the nucleoid, but the chromosome appears to be much more dynamic and irregular in structure than eukaryotic chromatin, reflecting the shorter cell cycle and very active metabolism of a bacterial cell. 

RGURE 25-18 Chromosome partitioning in bacteria, (a) All replication is carried out at a central replication factory that includes two complete replication forks, (b) The two replicated copies of the bacterial chromosome are extruded from the replication factory into the two halves of the cell, possibly with each newly synthesized origin bound separately to different points on the plasma membrane. Sequestering the two chromosome copies in separate ceil halves facilitates their proper segregation at ceil division. 

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