Microbial Genetics!Microbial Genome!What do cells do with their DNA?!§Replication ••Exact duplication of DNA molecule(s) in preparation for cell division §Gene expression ••Using the code to make proteins, mRNAs, rRNAs, tRNAs Gene Expression!!!!Terms!§Gene - segment of DNA that codes for 1 protein §DNA polymerase - enzyme that synthesizes (replicates) DNA §RNA polymerase - enzyme(s) that synthesizes RNA. Uses DNA as a template §mRNA (messenger RNA) - RNA transcribed from DNA that contains the code used in translation!Control of Gene Expression in Prokaryotes!§Why? —Some gene products (proteins) not needed all the time ---Maladaptive and energetically wasteful to make a product that is not needed §Prokaryotic cells such as bacteria are in changing environments —Turn on gene expression when energy compounds present in environment express genes needed for their uptake and utilization ---Turn off gene expression when compound present in environment and cell no longer needs to synthesize that compound Control of Gene Expression in Prokaryotes!§How? - Transcriptional control —Control when certain genes are transcribed (control when mRNA is synthesized by controlling the polymerase enzyme) §Operons clustered genes that encode enzymes needed for a metabolic pathway as well as genes involved in the pathway’s transcriptional control Operon!§Two basic operon types —Inducible when substance present - turn on operon ---Repressible when substance present - turn off operon !!!Lac Operon!§An inducible operon when lactose present transcribe the genes. §The Lac Operon an Inducible Operon §Genes code for proteins which process lactose for energy Repressible Operon!§Example: arg (arginine) & trp (tryptophan) operon -genes code for enzymes involved in the biosynthesis of amino acid !Mutations!§Mutation: any change is the base sequence of DNA Types of mutation —point mutation (nucleotide substitution)!---frameshift mutation (nucleotide deletion or addition) §May or may not change the final DNA product the protein!-Most mutations are deleterious!—only a rare few can be advantageous! How can Mutations be Important in Microbiology?!§Most mutations will kill a cell or make it function poorly. -Because microorganisms like bacteria can reproduce so rapidly (exponential growth under ideal conditions) a rare but beneficial mutation can arise. -These beneficial mutations may help a pathogen become more dangerous or harder to treat. Point Mutations! !!!!!!!Causes of Mutations!§Spontaneous (1 mutation per 10^5-10^10 cell divisions) —Mistakes in DNA replication --Background radiation ••radioactive minerals •ultraviolet light (UV)!§Induced exposure to mutagens above background levels —Radiation ••UV light, gamma rays, X-rays —Chemicals••nitrogenous base analogs •intercalating agents •methylating and deaminating agents Intermicrobial Gene Transfer!DNA Recombination Events in Bacteria Intermicrobial Gene Transfer!§Method in which bacterial cells share/exchange genetic information (DNA) —Leads to recombination (rearrangement of DNA) §Allows for new traits (often beneficial to the bacteria) to be acquired —Pilus formation ---Capsule formation ---Toxin production ---Enzyme production ---Antibiotic resistance Methods of Gene Transfer!§Conjugation, Transformation, Transduction Conjugation!§Transfer of genes through conjugation pilus Plasmids most commonly transferred Sometimes portions of the chromosome (Hfr transfer) F plasmid and conjugation!!!!Transformation!žUptake and incorporation of free DNA fragments or free plasmids Transduction!§Transfer of bacterial DNA by a virus —Bacteriophage: a virus which infect bacteria --Virus acts as a shuttle ••Move bacterial DNA from one cell to another §Two types of Transduction —Generalized ••Incorporation of random segments of DNA —Specialized ••Incorporation of specific segments of DNA Generalized Transduction!!!Genetic Engineering!Genetic Engineering!§Recombinant DNA—a segment of genetic information containing DNA from two different species of organisms §Goals: !—to produce gene products (proteins) that are beneficial to humans!--to produce organisms with attributes that are beneficial to humans --treatment of certain human diseases!!Microbes and Recombinant DNA!1. ••Microbes are altered with DNA from other species. —Microbes that produce human proteins!••hormones: insulin, growth factor!•blood clotting factors!—Microbes that produce other proteins!••vaccines!•drugs - antibiotics, anticancer drugs!—Microbes that perform specific tasks!••degrade pollution - oil spills, toxic compounds!•bacteria and viruses as “natural” pesticides!Microbes and Recombinant DNA!2. ••Microbe DNA (the vector) as a vehicle to transfer foreign DNA to animals or plants!—Microbe DNA = bacterial plasmids or viral genome!General procedure:!••Foreign gene inserted into microbe DNA!•microbe then used to carry and transfer foreign gene to plant or animal cells —Viruses used to transfer genes to eukaryotic cells --Retroviruses, adenoviruses —A bacterium, Agrobacterium tumifaciens, used to transfer genes to plants (vector is a plasmid)!Microbes and Recombinant DNA!§Example using a virus vector —gene therapy ••~treatment of certain genetic disorders by insertion of functional gene in cells with defective genes -treatment of disease by correcting faulty genes -certain cancers and immunodeficiency diseases -single gene inherited defects -ADA •Cystic fibrosis!-therapies have met with mixed results !Microbes and Recombinant DNA!3. ••Microbe genes inserted into animals and plants ••Examples••Bt corn •Mastitis resistant cows (lysostaphin gene) Producing Recombinant DNA!§Makes use of two important enzymes!—restriction endonucleases! --DNA ligase! End!§Go to: Infection and