Chapter Microbial genetics 8.1 DNA as genetic material 8.2 Mutation 8.3 DNA repair
Chapte8 Microbial genetics 8.1 DNA as genetic material 8.2 Mutation 8.3 DNA repair
Microbial molecular biology and genetics a clone: a population of cells that are derived asexually from a parental cell and are genetically identical Genome: all the genes present in a cell or virus Central dogma: DNA→>RNA→> protein transcription translation
Microbial molecular biology and genetics • A clone: a population of cells that are derived asexually from a parental cell and are genetically identical. • Genome: all the genes present in a cell or virus. • Central dogma: DNA→RNA → protein transcription translation
8.1 dNA as genetic material Coll t No capsule mooth (S) Lie S strain Live R Live R strain Heat→kled Heat-killed s strain Livo S and R strains isolated from dead Figure 1l.1 Grifmith's Transformation Experiments. (a) Mice died of pneumonia when injected with pathogenic strains of s pneumococci, which have a capsule and form smooth-looking colonies. (b) Mice survived when injected with a nonpathogenic strain of R pneumocoeci,whic lacks a capsule and forms rough colonies. (e) Injection with heat-killed strains of S pneumococci had no effect. (d) Injection with a live R strain and a heat-killed S strain gave the mice pneumonia. and live S strain pneumococci could be isolated from the dead mice
8.1 DNA as genetic material
R cells+ purified s cell polysaccharide R colonies R cells purified S cell protein R colonies R cells purified s cell RNA R colonies R cells purified S cell DNA S colonies S cell extract protease +R cells S colonies S cell extract + RNase +R cells S colonies Figure 11. 2 Experiments on the Transforming Principle. Summary of the experiments of Avery, MacLeod, and McCarty on the transforming principle. DNA alone changed R to S cells, and this effect was lost when the extract was treated with deoxyribonuclease. Thus DNA carried the genetic information required for the R to S conversion or transformation
The hershey-Chase experiments s protein DNA Blender treatment coat Protein DNA Blendor treatment
The Hershey-Chase experiments
RNA as genetic material TMV
RNA as genetic material • TMV
8.2 Mutations and mutants phenotypic expression, a mutation is a stable, heritableor Mutations: initially characterized as altered phenotypes change in the nucleotide sequence of dna Phenotype: the observable characteristics of an organism designated by a capital letter followed by two small letters. with either a plus and minus superscript to indicate the presence or absence of that property: His Glut et al Genotype: The precise genetic make-up of an organism designated by three lower case letters followed by a capital letter(all in italics) indicating the particular gene involved hisC, mutations in the hisc gene would be designated as hisel, hisc2 et al
8.2 Mutations and Mutants • Mutations: initially characterized as altered phenotypes or phenotypic expression, a mutation is a stable, heritable change in the nucleotide sequence of DNA. • Phenotype: the observable characteristics of an organism – designated by a capital letter followed by two small letters, with either a plus and minus superscript to indicate the presence or absence of that property: His- , Glu+ et al. • Genotype: The precise genetic make-up of an organism – designated by three lower case letters followed by a capital letter (all in italics) indicating the particular gene involved: hisC, mutations in the hisC gene would be designated as hisC1, hisC2 et al
Types of mutations Conditional mutations: those that are expressed only under certain environmental conditions eg. E coli: a conditional lethal mutant, low temperature grow; high temperature die Biochemical mutations: those causing a change in the biochemistry of the cell. Mutations make a microorganism unable to grow on a medium lacking an adequate supply of the pathway's end product auxotrophs: the mutant cannot grow on minimal medium(MM) and requires nutrient supplements prototrophs: microbial strains that can grow on MM Resistant mutant: a particular type of biochemical mutant that acquires resistance to some pathogen chemical. or antibiotic
Types of mutations • Conditional mutations: those that are expressed only under certain environmental conditions. eg. E.coli: a conditional lethal mutant, low temperature grow; high temperature die. • Biochemical mutations: those causing a change in the biochemistry of the cell. Mutations make a microorganism unable to grow on a medium lacking an adequate supply of the pathway’s end product. auxotrophs: the mutant cannot grow on minimal medium (MM) and requires nutrinent supplements. prototrophs: microbial strains that can grow on MM. • Resistant mutant: a particular type of biochemical mutant that acquires resistance to some pathogen, chemical, or antibiotic
Mutations occur in one of two ways Spontaneous mutations: arise occasionally in all cells and develop in the absence of any added agent 2. Induced mutations: the result of exposure of the organism to some physical or chemical agent called a mutagen
Mutations occur in one of two ways: • 1. Spontaneous mutations: arise occasionally in all cells and develop in the absence of any added agent. • 2. Induced mutations: the result of exposure of the organism to some physical or chemical agent called a mutagen
Spontaneous mutations without exposure to external agents 1. Errors in dna replication 2. The action of transposons 3. Frameshifts by the deletion or addition of bases 4. The insertion sequences of DNA segments into genes
Spontaneous mutations without exposure to external agents • 1. Errors in DNA replication • 2. The action of transposons • 3. Frameshifts by the deletion or addition of bases • 4. The insertion sequences of DNA segments into genes
