Copyright © 2011 Pearson Education Inc. Lecture prepared by Mindy Miller-Kittrell, University of Tennessee, Knoxville M I C R O B I O L O G Y WITH DISEASES BY TAXONOMY, THIRD EDITION Chapter 7 Microbial Genetics

Copyright © 2011 Pearson Education Inc. Gene Mutation  Gene Mutation – a change in the sequence of bases within a gene  May have neutral, beneficial, or harmful effects (Almost always harmful)  May result in a change in amino acid or a nonfunctional protein  Some mutations are repaired by excising the mutant nucleotides  Rarely leads to a protein having a novel property that improves ability of organism and its descendents to survive and reproduce

Copyright © 2011 Pearson Education Inc. Types of Gene Mutations Point mutations (most common) – – A single base at one point in the DNA sequence is inserted, deleted, or substituted by another base Frameshift mutations – (a type of point mutation) – One or several base pairs are deleted or inserted into the DNA sequence – Shifts the “translational reading frame”

Copyright © 2011 Pearson Education Inc. Point mutations – 3 types 1. Silent Mutation - the change in the codon but no change in amino acid; due to code redundancy 2.Missense Mutation - the change in the codon changes the amino acid thus the protein 3.Nonsense Mutation - the change in the codon change amino acid to Stop codon Types of Gene Mutations

Copyright © 2011 Pearson Education Inc. The effects of the various types of point mutations Figure 7.23

Copyright © 2011 Pearson Education Inc. The Frequency of Mutation Spontaneous mutation rate 1 in 10 9 (10 -9 ) replicated base pairs or 1 in 10 6 (10 -6 ) replicated genes Mutagens (agents that cause a mutation) increase mutation rate to 10 –5 or 10 –3 per replicated gene

Copyright © 2011 Pearson Education Inc. Mutations of Genes Animation: Mutagens

Copyright © 2011 Pearson Education Inc. Mutagens Chemicals : – Nitrous acid – –mutates adenine to guanine – Base analogs – – mimic nitrogenous base; disrupt DNA and RNA replication and cause point mutations –ex. 5 bromo uracil – Smoke/ethidium bromide –causes insertion or deletion of base pairs –Results in frameshift mutations

Copyright © 2011 Pearson Education Inc. Nitrogen Base Analog

Copyright © 2011 Pearson Education Inc. Mutagens Environment: – Ionizing radiation – (X rays and gamma rays) –Causes ion formations that react with bases and deoxyribose- phosphate backbone –induces breaks in chromosomes – Nonionizing radiation –(UV rays) – causes thymine to crosslink resulting in thymine dimers –Cause errors in replication and transcription –The most common type of mutation

Copyright © 2011 Pearson Education Inc. The action of a frameshift mutagen Figure 7.26

Copyright © 2011 Pearson Education Inc. Transfer of Genetic Information Horizontal gene transfer

Copyright © 2011 Pearson Education Inc. Gene transfer mechanisms – Vertical Gene Transfer – – Occurs in cell division; passing on gene’s to offspring – Horizontal Gene Transfer – – Exchanging gene’s within the same generation – Results in a recombinant cell that has received DNA from another cell

Copyright © 2011 Pearson Education Inc. Horizontal Gene Transfer 1. Transformation - transfer of naked DNA fragments 2. Transduction- mediated through a bacteriophage 3. Conjugation- transfer of DNA through a pilus 4. Transposition- migration of DNA “jumping genes”

Copyright © 2011 Pearson Education Inc. Griffith’s Experiments of Transformation Figure 7.30

Copyright © 2011 Pearson Education Inc. Transformation Transfer of naked DNA fragments (from environment) to cell Cells must be competent (able to take up the DNA)

Copyright © 2011 Pearson Education Inc. Transduction Figure 7.31 Mediated through a bacteriophage

Copyright © 2011 Pearson Education Inc. Bacterial Conjugation Figure 7.32a Transfer of DNA through a pilus

Copyright © 2011 Pearson Education Inc. Plasmids Figure 4.6a, b Nucleoid region Plasmid

Copyright © 2011 Pearson Education Inc. Types of Plasmids – F (fertility) factor – Carries genes for sex pili and transfer of the plasmid – R (resistance) factor – Encodes antibiotic resistance – Bacteriocin factor – – Encodes for toxin that kills bacterial cell of the same or similar species that lack that factor – Virulence factor – – Encode for enzymes, structures or toxins that make bacteria pathogenic

Copyright © 2011 Pearson Education Inc. Conjugation

Copyright © 2011 Pearson Education Inc. Hfr plasmid Conjugation Hfr plasmid incorporates directly into the host genome so increases probability of recombination Figure 7.33  Conjugation

Copyright © 2011 Pearson Education Inc. Transposition Figure 7.36  Transposons are segments of DNA that can move from one region of DNA to another  They contain insertion sequences (palindromic) for cutting and resealing DNA hill.com/sites/ /student_view0/chapter13/animation_quiz_5.html

Copyright © 2011 Pearson Education Inc. Figure 7.36a-c a. Insertion sequence b. Simple Transposon c. Complex Transposon Transposons