Bio 141.docx

Exchange of Genetic Information: - Sexual processes in microorganisms increase the chances that rare mutations occur together in a single microbe, subjecting them to natural selection. - Genetic interactions between microbes allow their genomes to evolve much faster than through mutation alone. - Me...

Exchange of Genetic Information: - Sexual processes in microorganisms increase the chances that rare mutations occur together in a single microbe, subjecting them to natural selection. - Genetic interactions between microbes allow their genomes to evolve much faster than through mutation alone. - Medical phenomena associated with genetic exchanges include the emergence and spread of antibiotic resistance plasmids, flagellar phase variation in Salmonella, and antigenic variation in Neisseria and Borrelia. Sexual Processes in Bacteria: - Genetic information transfers from a donor to a recipient, resulting in either the substitution of donor alleles for recipient alleles or the addition of donor genetic elements to the recipient genome. - Transformation, transduction, and conjugation are methods that introduce donor DNA into recipient bacteria. Recombination is often necessary for donor DNA to persist in the recipient, especially when donor and recipient bacteria are closely related. Genetic Mapping and Analysis: - Linkage testing is conducted to analyze nonrandom reassortment of parental alleles in recombinant progeny, aiding in the construction of genetic maps. - The genome of E. coli is circular, and genetic and physical maps have been established through genetic linkage and biochemical analysis. These maps are used to analyze both chromosomal and extrachromosomal elements such as bacteriophages and plasmids. Restriction-Modification Systems: - Comprise modifying enzymes that methylate specific DNA sequences and restriction endonucleases that cleave foreign DNA lacking these modifications. - Serve as a defense mechanism against phage infection or unwanted plasmid incorporation, potentially preventing genetic exchanges between different strains or species. Transformation: - Involves the uptake of DNA released from donor bacteria by recipient bacteria from their environment. - For DNA to be active in transformation, it must be at least 500 nucleotides long. Transformation activity is rapidly lost if DNA is treated with deoxyribonuclease. - Transformation was first discovered in Streptococcus pneumoniae and is variable among bacteria, influenced by their physiological state. Transduction: - Bacteriophages introduce DNA from donor bacteria into recipient bacteria. This can occur via generalized transduction, where random bacterial DNA is packaged into phages, or specialized transduction, which involves specific genes transferred by temperate phages. - Generalized transducing phages can cause either abortive or complete transduction, influencing how donor genes are expressed in recipient cells. Conjugation: - Direct contact between bacteria leads to the formation of a cytoplasmic bridge, facilitating DNA transfer. - The F plasmid in E. coli exemplifies fertility plasmids, enabling the transfer of DNA during mating, influenced by specific transfer genes. - High-frequency recombination (Hfr) strains demonstrate efficient transfer of chromosomal genes due to the integration of the F plasmid into the bacterial chromosome. Recombination: - Recombination involves the breakage and joining of DNA from different genomes, resulting in hybrid, recombinant DNA. - Generalized recombination occurs between homologous DNA sequences, while site-specific recombination happens at specific DNA sites. Illegitimate recombination involves nonhomologous DNA and can lead to genetic anomalies. Transposons: - Mobile DNA segments that can integrate into various DNA sites, influencing mutation and genomic rearrangement. - Transposons play a significant role in bacterial adaptation by facilitating gene acquisition and dissemination within bacterial populations. - They are categorized into classes based on structure and function, ranging from simple insertion sequences to complex transposons containing additional genes for antibiotic resistance or virulence. These notes provide a comprehensive understanding of genetic exchange mechanisms in bacteria, their implications for evolution and medicine, and the molecular tools bacteria use to facilitate and control genetic material transfers.