genetics of bacteria and viruses

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презентация powerpoint chair of microbiology, virology, and immunology genetics of bacteria and viruses bases of biotechnology and gene engeneering * lectures schedule 1. structure of bacterial genome. 2. extrachromosomal elements. 3. mutations. 4. recombinations. 5. gene engineering. * f. crick i j. watson – described dna structure * dna structure * e. coli dna the chromosome of e. coli has a contour length of approximately 1.35 mm, several hundred times longer than the bacterial cell, but the dna is supercoiled and tightly packaged in the bacterial nucleoid. the time required for replication of the entire chromosome is about 40 minutes * e. coli dna * definition: extrachromosomal genetic elements that are capable of autonomous replication (replicon) episome - a plasmid that can integrate into the chromosome they are usually much smaller than the bacterial chromosome, varying from less than 5 to more than several hundred kbp. most plasmids are supercoiled, …

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ributed randomly between daughter cells at division. some plasmids are cryptic and have no recognizable effects on the bacterial cells that harbor them * * transposable genetic elements definition: segments of dna that are able to move from one location to another properties “random” movement not capable of self replication transposition mediated by site-specific recombination transposase transposition may be accompanied by duplication * types of transposable genetic elements insertion sequences (is) definition: elements that carry no other genes except those involved in transposition nomenclature - is1 structure importance mutation plasmid insertion phase variation the known insertion sequences vary in length from approximately 780 to 1500 nucleotide pairs, have short (15-25 base pair) inverted repeats at their ends, and are not closely related to each other. transposase abcdefg gfedcba * phase variation in salmonella h antigens is h1 gene h2 gene h1 flagella h2 flagella * types of transposable genetic elements …

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and inactivates it, transposons have a major role in causing deletions, duplications, and inversions of dna segments as well as fusions between replicons. in medically important bacteria, genes that determine production of adherence antigens, toxins, or other virulence factors, or specify resistance to one or more antibiotics, are often located in complex transposons. well-known examples of complex transposons are tn5 and tn10, which determine resistance to kanamycin and tetracycline, respectively. mutation is a stable, heritable change in the genomic nucleotide sequence * how do mutations occur? spontaneous mutations - arise occasionally in all cells; are often the result of errors in dna replication (random changes) frequency of naturally occurring (spontaneous) mutation varies from 10-6 to 10-9 (avg = 10-8) this means that if a bacterial population increases from 108 to 2 x 108, on the average, one mutant will be produced for the gene in question. induced mutations - arise …

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rd mutation: a mutation that alters phenotype from wild type reverse mutation: a second mutation which may reverse wild phenotype and genotype (in same gene) suppressor mutation: a mutation that alters forward mutation, reverse wild phenotype (in same gene - intragenic, in another gene - extragenic) * morphological mutations-result in changes in colony or cell morphology lethal mutations - result in death of the organism conditional mutations - are expressed only under certain environmental conditions biochemical mutations - result in changes in the metabolic capabilities of a cell 1) auxotrophs - cannot grow on minimal media because they have lost a biosynthetic capability; require supplements 2) prototrophs - wild type growth characteristics resistance mutations-result in acquired resistance to some pathogen, chemical, or antibiotic mutations affect bacterial cell phenotype * induced mutations-caused by mutagens mutagens – molecules or chemicals that damage dna or alter its chemistry and pairing characteristics base analogs …

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ysical agent action uv irradiation causes formation of adjacent t-t dimers that distorts the dna backbone, altering the binding properties of bases near the dimer x-ray alters bases chemically, causes deletions and induces breaks in dna chain * examples of mutagens biological agent action insertion sequences (is) pieces of dna about a thousand nucleotide bases in length which can insert into a genetic sequence transposons genetic elements goverened by is which can insert into the chromosome within a gene viruses some bacteriophage (e.g. phage µ) can integrate their dna into random positions in the bacterial chromosome * mutant detection in order to study microbial mutants, one must be able to detect them and isolate them from the wild-type organisms visual observation of changes in colony characteristics mutant selection - achieved by finding the environmental condition in which the mutant will grow but the wild type will not (useful for isolating …

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презентация powerpoint chair of microbiology, virology, and immunology genetics of bacteria and viruses bases of biotechnology and gene engeneering * lectures schedule 1. structure of bacterial genome. 2. extrachromosomal elements. 3. mutations. 4. recombinations. 5. gene engineering. * f. crick i j. watson – described dna structure * dna structure * e. coli dna the chromosome of e. coli has a contour length of approximately 1.35 mm, several hundred times longer than the bacterial cell, but the dna is supercoiled and tightly packaged in the bacterial nucleoid. the time required for replication of the entire chromosome is about 40 minutes * e. coli dna * definition: extrachromosomal genetic elements that are capable of autonomous replication (replicon) episome - a plasmid …

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