Slide 1Why is this important?The Structure and Replication of GenomesStructure of Prokaryotic GenomesThe Structure of Eukaryotic GenomesDNA ReplicationThe Relationship Between Genotype and PhenotypeThe Transfer of Genetic InformationThe Events in TranscriptionThe Genetic CodeThe Genetic CodeRegulation of Genetic ExpressionMutations of GenesTypes of MutationsTypes of MutationsMutagensFrequency of MutationGenetic Recombination and TransferHorizontal Gene Transfer Among ProkaryotesTransformationTransformationTransductionTransductionTransductionTransductionBacterial ConjugationBacterial ConjugationBacterial ConjugationBacterial ConjugationM I C R O B I O L O G YWITH DISEASES BY BODY SYSTEM SECOND EDITIONChapter 7Microbial GeneticsTHIRDWhy is this important?•DNA replication, transcription, and translation are all types of polymerization reactions that utilize large amounts of energy for a cell•Mutations promote inheritable change•Bacteria can share genetic material and this is one way antibiotic resistance can spread in the environmentThe Structure and Replication of Genomes•Genetics – study of inheritance and inheritable traits as expressed in an organism’s genetic material•Genome – the entire genetic complement of an organism–Includes its genes (specific sequences of nucleotides that code for polypeptides or RNA molecules) and nucleotide sequences that connect genes to one anotherStructure of Prokaryotic Genomes•Prokaryotic chromosomes–Main portion of DNA, along with associated proteins and RNA, packaged in 1-2 distinct chromosomes–Prokaryotic cells have a single copy of each chromosome (haploid)–Typical chromosome – circular molecule of DNA in nucleoid•Plasmids–Small molecules of DNA that replicate independently of the chromosome–1-5% of the size of a prokaryotic chromosome–Carry information required for their own replication, and often for one or more cellular traits–Typically not essential for normal metabolism, growth, or reproduction, but can confer survival advantagesThe Structure of Eukaryotic Genomes•Nuclear chromosomes–Typically have more than one nuclear chromosome in their genomes–Chromosomes are linear and sequestered within membrane-bound nucleus–Eukaryotic cells most often have two copies of each chromosome (diploid)•Extranuclear DNA of eukaryotes–DNA molecules of mitochondria and chloroplasts are circular and resemble chromosomes of prokaryotes–Only code for about 5% of RNA and proteins–Nuclear DNA codes for 95% of RNA and proteins–Some fungi and protozoa carry plasmidsDNA Replication•An anabolic polymerization process that requires monomers and energy–Triphosphate deoxyribonucleotides serve both functions•Key to replication is complementary structure of the two strands–A-T and G-C•Replication is semiconservative – new strands composed of one original strand and one daughter strandThe Relationship Between Genotype and Phenotype•Genotype – set of genes in the genome–Consists of all the series of DNA nucleotides that carry instructions for an organism’s life•Phenotype – physical features and functional traits of the organism–Includes characteristics such as structures, morphology, and metabolism•Genotype determines phenotype by specifying what kinds of RNA and which structural, enzymatic, and regulatory protein molecules are producedThe Transfer of Genetic Information•Transcription – information in DNA is copied as RNA nucleotide sequences•Translation – polypeptides synthesized from RNA nucleotide sequences•Both transcription and translation are anabolic polymerization reactions•Central dogma of genetics–DNA transcribed to RNA–RNA translated to form polypeptidesThe Events in Transcription•Prokaryotes–Occurs in the nucleoid–Single type of RNA polymerase•Eukaryotes–Occurs in the nucleus (nucleolus), mitochondria and chloroplasts–Three types of nuclear RNA polymerases–Mitochondria use a fourth type of RNA polymerase–At least 5 transcription factors aid in binding eukaryotic RNA polymerase to promoter sequences–mRNA processed before translationThe Genetic CodeThe Genetic CodeRegulation of Genetic Expression•Most of a bacterium’s genes are expressed at all times–Constantly transcribed and translated•Other genes are regulated so that the polypeptides they encode are synthesized only in response to a change in the environment–Allows cell to conserve energy•Regulation of protein synthesis–May stop transcription of mRNA–Can stop translation directlyMutations of Genes•Mutation – change in the nucleotide base sequence of a genome•Mutations of genes are almost always deleterious, though some make no difference to the organism•Rarely leads to a protein having a novel property that improves ability of organism and its descendants to survive and reproduceTypes of Mutations•The most common type of mutation is a point mutation in which a single base pair is affected–Base pair substitutions–Insertions Frameshift mutations–Deletions•Frameshift mutations affect proteins much more seriously than mere substitutions because a frame shift affects all codons subsequent to the mutationTypes of MutationsMutations: TypesMutagens•Mutations occur naturally during the life of an organism–Spontaneous mutations – result from errors in replication and repair–Recombination – relatively long stretches of DNA move among chromosomes, plasmids, and viruses, introducing frameshift mutations•Physical or chemical agents called mutagens, which include radiation and several types of DNA-altering chemicals, induce mutationsFrequency of Mutation•Mutations are rare events, otherwise organisms could not effectively reproduce themselves–About one of every 10 million genes contains a mutation•Mutagens increase the mutation rate by a factor of 10 to 1000 times•Many mutations are deleterious because they code for nonfunctional proteins or stop translation entirely•Rarely, a cell acquires a beneficial mutation that allows it to survive, reproduce, and pass the mutation to its descendants–This change in gene frequency in a population is evolutionGenetic Recombination and Transfer•Genetic recombination – refers to the exchange of nucleotide sequences between two DNA molecules and often involves segments that are composed of identical or nearly identical nucleotide sequences (homologous sequences)•Recombinants – cells with DNA molecules