Bacterial Genetics PDF

MUTATION (REcaps) Mutation is a change in the base sequence of DNA that usually results in the insertion of a different amino acid into a protein and the appearance of an altered phenotype Base substitution -MISSENSE MUTATION Mutation due to base substitution results in a codon that simply causes...

MUTATION (REcaps) Mutation is a change in the base sequence of DNA that usually results in the insertion of a different amino acid into a protein and the appearance of an altered phenotype Base substitution -MISSENSE MUTATION Mutation due to base substitution results in a codon that simply causes different amino acids to be inserted Occurs when one base is inserted in the place of another I HAVE A CAT = Normal DNA sequence I HAVE A RAT = Missense mutation Base substitution -NONSENSE MUTATION Nonsense mutation is a mutation due to base substitution, results when the base substitution generates a termination codon that stops protein synthesis prematurely. FRAMESHIFT MUTATION Frameshift mutation occurs when one or more base pairs are inserted or deleted, which shifts the reading frame on the ribosome Frameshift mutation can change every amino acid that follows the point of mutation and can alter a protein so much that it is unable to perform its normal functions Insertion mutation occurs when extra nucleotides are put into a DNA sequence, making it longer than it should be Deletion mutation occurs when a part or a sequence of DNA is lost during DNA replication INSERTION THE FAT CAT ATE THE RAT THE FAT CAR TAT ETH ERA T DELETION THE FAT CAT ATE THE RAT THE FAT ATA TET HER AT PLASMID Extrachromosomal DNA substances. Capable of replicating independently of the bacterial chromosomes. Control medically important properties of pathogenic bacteria including: ● resistance to antibiotic ● production of toxins ● synthesis of cell surface structures required for adherence or colonisation TRANSFER OF DNA WITHIN BACTERIAL CELLS TRANSFER OF DNA WITHIN BACTERIAL CELLS -Transposons Transposable elements (TEs), also known as "jumping genes" or transposons, are sequences of DNA that move (or jump) from one location in the genome to another These newly inserted pieces of DNA can cause profound changes in the genes into which they insert and in an adjacent gene There are two distinct types: • CLASS II TRANSPOSONS (‘cut – and – paste’) Consists of DNA that moves directly from place to place • CLASS I TRANSPOSONS (‘copy – and – paste’) Retrotransposons that  first transcribe the DNA into RNA and then use reverse transcriptase to make a DNA copy of the RNA to insert in a new location TRANSFER OF DNA WITHIN BACTERIAL CELLS –Programmed rearrangements • Consist of the movement of a gene from the silent storage site to an active site (transcription and translation occur). • Many silent genes encode variants of antigens. • The insertion of the new gene into the active site is the source of the consistent antigenic variation. TRANSFER OF DNA BETWEEN BACTERIAL CELLS Discrete DNA segments that establish horizontally transferred genes in a population. This region may integrate into the chromosome of the host; excised and transferred to a new host by transformation, conjugation or transduction. GENOMIC ISLAND Horizontal gene transfer, or swapping genetic material between neighbouring “contemporary” bacteria, is another way resistance can be acquired. Many of the antibiotic resistance genes are carried on plasmids, transposons or integrons that can act as vectors that transfer these genes to other members of the same bacterial species, as well as to bacteria in another genus or species. HORIZONTAL GENE TRANSFER CONJUGATION TRANSFORMATION TRANSDUCTION