Bacterial Genetics PDF

Bacterial Genetics  GENETICS inheritance variation  All inherited characteristics are encoded in DNA. Bacterial Nucleic Acids DNA RNA t RNA Chromosome r RNA Plasmids...

Bacterial Genetics  GENETICS inheritance variation  All inherited characteristics are encoded in DNA. Bacterial Nucleic Acids DNA RNA t RNA Chromosome r RNA Plasmids m RNA  Bacterial Chromosome It is a single, supercoiled, circular double stranded helix of DNA molecule Genetic information is stored as sequence of bases in this molecule  GENE Unit of heredity Segment of DNA that carries information for a specific biochemical or physiologic property. Carried on the bacterial chromosome. Essential for bacterial growth.  Plasmids Definition Properties Functions  DEFINITION & PROPERTIES Extrachromosomal Small circular Double stranded helical DNA Do not code for essential function for survival of the bacteria Separate replicon or Episome  FUNCTIONS Antibiotic resistance (R factor) Toxin production Bacteriocines (toxic proteins that kill some other bacteria) Some surface antigens  Variation observable change within a species Phenotypic Genotypic Mutation Genetic Transfer Within same cell Between cells (Transposition) -Transformation -Conjugation -Transduction  Phenotypic Variation The genes are not modified Their expression is changed in response to environmental conditions ( sporulation)  Genotypic variation - Genetic alteration - Heritable Mutation Alteration of the nucleotide sequence at some point in the organism’s DNA Occurs spontaneously but could be induced by physical or chemical agents. It is heritable Types : base substitution, frame shift, insertion, deletion. Physical Agents : 1. Heat 2. Irradiations(U.V. or ionizing) Chemical Agents 1. Ethidium bromide 2. Nitrous oxide  Genetic Transfer In same cell Between Cells Transposition Transformation Transduction Conjugation Transposition  Transposable Elements Transposable elements (transposons=jumping genes) move from one DNA site to another within the genome of the same organism, where they can integrate into DNA at random.  Transformation It is the release of DNA from dead cells by lysis, followed by its uptake by recipient cells. Recipient cells must be competent Any gene could be transformed  Transduction Bacteriophages (viruses that infect bacteria) act as vectors to transfer DNA from donor to recipient bacteria  Phage genes can cause changes in the phenotype of the host bacterium; - Toxin production in Corynebacterium diphtheriae is controlled by a phage gene. - Production of β-lactamase is mediated by plasmids are transferred between staphylococci by transduction  Conjugation It is plasmid mediated mating (joining) of two bacteria, with transfer of DNA from donor to recipient cell through direct wall to wall contact and formation of a sex pilus The mating process is controlled by an F (fertility) plasmid, which carries the genes for the proteins required for mating, (protein pilin), which forms the sex pilus (conjugation tube) During mating, the pilus of the donor (male) bacterium carrying the F factor (F+) attaches to a receptor on the surface of the recipient (female) bacterium. The latter is devoid of an F plasmid (F−) Then the F Plasmid DNA is cleaved enzymatically, and one strand is transferred across the bridge into the female cell. The process is completed by synthesis of the complementary strand to form a double- stranded F plasmid in both the donor and recipient cells. The recipient now becomes an F+ male cell that has the ability to transmit the plasmid further. The new DNA can integrate into the recipient’s DNA and become a stable component of its genetic material.  Recombination Successful gene transfer must be followed by RECOMBINATION = integration of the transferred genetic element into the recipient DNA thus maintaining its existence in the following progeny.  OTHERWISE abortive genetic transfer → the transferred DNA remains for a short period without replication → diluted out. Genetic Transfer between cells THANK YOU