Bacteria chromosomes

Isophorone does not induce gene mutations in bacteria, chromosomal aberrations in vitro, DNA repair in primary rat hepatocytes, or bone marrow micronuclei in mice. Positive effects were observed only in the absence of an exogenous metabolic system in L5178YTK+/— mouse mutagenesis assays as well as in a sister chromatid exchange assay. The weight of evidence of all mutagenicity data supports the contention that isophorone is not a potent DNA-reactive compound. ... 

Level 1 3 mutagenicity tests gene mutation in bacteria, chromosomal aberration in mammalian cells (in vitro), gene mutation in mammalian cells (in vitro)... 

Staining Applications Brain spinal cord bacteria chromosomes nicotinic acetylcholine receptor nucleic acids phosphates polyphosphates tocopherol tocopherol acetate ... 

For efficient genetic engineering, the plasmid DNA should be obtainable at high levels. Some plasmids are found only as three or four copies per cell. More useful are plasmids which have a high cellular copy number, e.g. 25-50 copies per cell. Techniques are available to amplify the copy number further. If an inhibitor of protein synthesis, e.g. chloramphenicol, is added to a culture of plasmid-containing bacteria, chromosomal, but not plasmid, DNA replication stops. The number of plasmids per cell thereby may increase to over one thousand. 

Imaging/Labeling Applications Nucleic acids " cells bacteria chromosome spreads nuclei " micronuclei megakaryocyte microorganisms sperms hairs ... 

Imaging/Labeling Applications Antibodies, " bacteria chromosomes histone deacetylase Hodgkin and Reed Sternberg (HRS) cells microorganisms nucleotides/nucleic acids peptides/proteins silver particles T lymphoc5de antigens " ... 

Bacteria produce chromosomady and R-plasmid (resistance factor) mediated P-lactamases. The plasmid-mediated enzymes can cross interspecific and intergeneric boundaries. This transfer of resistance via plasmid transfer between strains and even species has enhanced the problems of P-lactam antibiotic resistance. Many species previously controded by P-lactam antibiotics are now resistant. The chromosomal P-lactamases are species specific, but can be broadly classified by substrate profile, sensitivity to inhibitors, analytical isoelectric focusing, immunological studies, and molecular weight deterrnination. Individual enzymes may inactivate primarily penicillins, cephalosporins, or both, and the substrate specificity predeterrnines the antibiotic resistance of the producing strain. Some P-lactamases are produced only in the presence of the P-lactam antibiotic (inducible) and others are produced continuously (constitutive). 

Clinically resistant bacteria, vktuaUy 100% of the Enterobacteriaceae produce a low level of chromosomal enzyme that can clinically be selected for higher levels. 

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)... 

Bacteria can develop resistance to antimicrobial agents as a result of mutational changes in the chromosome or via the acquisition of genetic material (resistance genes carried on plasmids or transposons or the recombination of foreign DNA into the chromosome) (Fig. 2). 

AAC Aminoglycosides, fluoroquinolones Gram-negative and gram-positive bacteria Plasmid, transposon, chromosome... 

Resistance to trimethoprim can be due to the acquisition of plasmid encoded non-allelic variants of the chromosomal DHFR enzyme that are antibiotic unsusceptible. The genes may be part of transposons that then insert into the chromosome. For instance, in gram-negative bacteria the most widespread gene is dhfrl on transposon Tn7. 

The chromosomes of Escherichia coli and other bacteria are single, double-stranded DNA molecules with a total length of more than 1,000 pm. Relaxed DNA exists as a helical molecule, with one full turn of the helix occurring approximately every 10.4 base pairs. This molecule must undergo several folding and compaction steps to fit into an E. coli cell which is only 1-3 pm long. Despite this enormous compaction, bacterial DNA must be accessible for the bacterial enzymes that catalize DNA replication and transcription... 

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. 

The majority of bacteria reproduce-by simple binary fission the circular chromosome divides into two identical circles which segregate at opposite ends ofthe cell. At the same time, the cell wall is laid down in the middle ofthe cell, which finally grows to produce two new cells each with its own wall and nucleus. Each ofthe two new cells will be an exact copy of the original cell from which they arose and no new genetic material is received and none lost. 

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