CHAPTER 7: MICROBIAL GENETICSWhy is this important?• DNA replication, transcription, and translation are all types of polymerizationreactions that utilize large amounts of energy for a cell• Metabolisms help provide this energy• Mutations promote inheritable change• Changes in base sequence of DNA and RNA • Bacteria can share genetic material and this is one way antibiotic resistance can spread in the environment • 3 different ways• All of them are types of horizontal gene transfer• One way antibiotic resistance can spread in an 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– Only have a nucleoid – no nucleus– Main portion of DNA, along with associated proteins and RNA, packaged in 1-2 distinct chromosomes– Prokaryotic cells have a single circular copy of each chromosome (haploid)– Typical chromosome – circular molecule of DNA in nucleoid• Plasmids– May or may not have them– Not required for growth, metabolism, or replication– 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 oneor more cellular traits– Typically not essential for normal metabolism, growth, or reproduction, but can confer survival advantages– Easily transferred from one organism to anotherThe Structure of Eukaryotic Genomes• Nuclear chromosomes– Typically have more than one nuclear chromosome – Chromosomes are all linear and sequestered within membrane-boundnucleus– Linear– Eukaryotic cells typically have two copies of each chromosome (diploid)– Presence of plasmids may occur in some fungi and protozoa, but are very rare • 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 in the total cell– Nuclear DNA codes for 95% of RNA and proteins in the total cell– Some fungi, algae, and protozoa carry plasmids– Much less common then prokaryotes– Chloroplasts and mitochondria do have extranuclear DNA and are in eukaryotic cells but only codes for about 5% of RNA and proteins for the cellDNA Replication• An anabolic polymerization process that requires monomers and energy– Triphosphate deoxyribo-nucleotides serve both functions• Provides energy• Serves as the monomers– Takes monomeric units and adds them to a chain to make polymers• Key to replication is complementary structure of the two strands– A-T– G-C– Add these monomers to a growing chain to make a polymer• Replication is semiconservative – new strands will always be composed of one original strand and one daughter strandTACGTATGATTGCCATATGCATACTAACGGTATACGTATGATTGCCATATGCATACTAACGGTAThe Relationship Between Genotype and Phenotype• Genotype – set of genes in the genome– Consists of all the series of DNA nucleotides that carry instructions foran organism’s life– Written word• Phenotype – physical features and functional traits of the organism – manifestation of the phenotype; our phenotype is different b/c genotype– 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 produced• Not all genes are active at all times; the information of a genotype is not always expressed as a phenotypeThe Transfer of Genetic Information• Replication: copy DNA– Base pairing has to be maintained (A-T; G-C for DNA)– RNA: A-U; G-C• Transcription: information in DNA is copied as RNA nucleotide sequences– DNA  RNA keep the same language (nucleotides)• Translation: polypeptides synthesized from RNA nucleotide sequences– RNA  amino acids; changing the language– Same information is being conveyed in a different form• Both transcription and translation are anabolic polymerization reactions• Central dogma of genetics– DNA transcribed to RNA– RNA translated to form polypeptides/proteins- TAC GCC ATG AAT (DNA)- AUG CGG UAC UUA (RNA)- Methionine/Arginine/Tyrosine/Leucine (protein)- Each grouping of 3 nucleotides is a codon- 22 naturally occurring amino acids- 64 possible codons - AUG is the start codon that initiates every proteino Prokaryotes: slight modification of methionine – N-formyl methionine or F-meto Eukaryotes: Methionine The Events In Transcription (takes place where the DNA is located)• Prokaryotes– Occurs in the nucleoid– Single type of RNA polymerase– Enzyme that copies DNA to RNA – A single transcription factor is required to bind RNA polymerase to DNA• Transcriptional Differences in Eukaryotes– Occurs in the nucleus (nucleolus), mitochondria and chloroplasts– Three types of nuclear RNA polymerases– Mitochondria use a fourth type of RNA polymerase– Several transcription factors aid in binding xeukaryotic RNA polymerase to DNA– Elongation factors required– mRNA processed before translationThe 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– If a cell is in a purely glucose environment there is no need to continuously produce lactose• Regulation of protein synthesis– May stop transcription of mRNA– Can stop translation directly• 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• Stopping transcription will save the most energy for the cell• Translation can also be stopped• Regulation of protein synthesis– May stop transcription of mRNA– Can stop translation directlyMutation of Genes• Mutation – change in the nucleotide base sequence of a