* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Lecture 11 - Horizontal Gene Transfer Chapt. 8 S11
Comparative genomic hybridization wikipedia , lookup
Promoter (genetics) wikipedia , lookup
Silencer (genetics) wikipedia , lookup
Maurice Wilkins wikipedia , lookup
Cell-penetrating peptide wikipedia , lookup
Gel electrophoresis of nucleic acids wikipedia , lookup
Molecular evolution wikipedia , lookup
List of types of proteins wikipedia , lookup
Community fingerprinting wikipedia , lookup
Non-coding DNA wikipedia , lookup
Nucleic acid analogue wikipedia , lookup
DNA vaccination wikipedia , lookup
Genomic library wikipedia , lookup
Molecular cloning wikipedia , lookup
DNA supercoil wikipedia , lookup
Deoxyribozyme wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
5/11/2011 Gene Transfer All Types of Gene Transfer • Involve unidirectional transfer of information (donor-->recipient) Why won’t the fragment shown below replicate in the cell? Donor Recipient 1 5/11/2011 DNA without an Origin Must Integrate into the Chromosome DNA without an Origin Must Integrate into the Chromosome Homologous recombination (site-specific recombination) Donor Recipient Plasmid (a replicon) 2 5/11/2011 All Types of Gene Transfer • Involve unidirectional transfer of information (donor-->recipient) • Transferred DNA must replicate to be passed onto daughter cells Gene Transfer in Bacteria • Genes are naturally transferred between bacteria using three mechanisms 1. Transformation 2. Transduction 3. Conjugation What is the transforming principle in Griffith’s experiments? “transforming principle” (DNA) 3 5/11/2011 DNA-Mediated Transformation Uptake of naked DNA Process is sensitive to the addition of DNAse Some species secrete DNA DNA-Mediated Transformation Uptake of naked DNA Process is sensitive to the addition of DNAse Recipient cell must be competent Natural competence Observed in only certain species Example - Streptococcus pneumoniae (GPC) •Becomes Becomes competent in late log phase •Competent cell binds ds DNA •Enzymes cut DNA into smaller fragments (5 - 15 kb) •Single strand is taken up by cell Example - Haemophilus influenzae (GNR) •Cell binds DNA only from related species Artificial competence In the laboratory, treat cells with specific chemicals (plasmids taken up) DNA-Mediated Transformation Uptake of naked DNA Process is sensitive to the addition of DNAse Recipient cell must be competent Some species secrete DNA 4 5/11/2011 Artificial Competence ¾Not all bacteria become naturally competent ¾In one technique called electroporation, bacteria and DNA are mixed together g Transduction DNA is transferred via a bacteriophage Generalized transduction - lytic or temperate phage Specialized transduction - temperate phage only Generalized Transduction Initial steps of a typical productive infection Wild-type phage Error in packaging Transducing particle carries bacterial DNA 5 5/11/2011 Specialized Transduction Initial steps generate a lysogen C D • Only DNA that flanks the site of integration can be excised with phage DNA • Some phage genes are left behind lysogen •begins lytic cycle •incorrect excision Specialized Transduction defective phage Initial steps generate a lysogen lysogen •begins lytic cycle •incorrect excision Lytic cyle: •replication of phage parts •assembly •release Specialized Transduction defective phage Initial steps generate a lysogen lysogen •begins lytic cycle •incorrect excision 6 5/11/2011 Specialized Transduction Initial steps generate a lysogen lysogen •begins lytic cycle •incorrect excision Transduction Generalized Specialized Error in excision Error in packaging Transducing particle carries bacterial DNA Defective phage Transduction - DNA transferred by a bacteriophage Transformation - uptake of naked DNA Gene Transfer in Bacteria • Genes are naturally transferred between bacteria using three mechanisms 1. Transformation 2. Transduction 3. Conjugation 7 5/11/2011 Conjugation Requires cell-to-cell contact Involves a conjugative plasmid F plasmid (fertility plasmid) serves as a model Three types of donors: F+ Hfr F′(won’t be covered in this course) Conjugation: F+ donor “male” “female” Conjugation: F+ donor Note: some R plasmids (encode resistance to one or more antibiotics) are conjugative F + + F- → F + + F+ In donor cell, replication replaces strand that’s being transferred In recipient cell, complement to transferred strand is synthesized 8 5/11/2011 Conjugation: Hfr donor Formation of an Hfr cell Hfr = High-frequency recombination Figure 8.25 Conjugation: Hfr donor • Some F plasmid DNA is transferred first, followed by chromosomal DNA • In donor cell, replication replaces strand that’s being transferred • In recipient cell, complement to transferred strand is synthesized Cells inevitably separate before entire chromosome is transferred Conjugation: Hfr donor Hf + F- → Hfr Hfr Hf + FSignificance of Hfr strains: •Chromosomal DNA transfer •Allowed mapping of E. coli chromosome 9 5/11/2011 Conjugation: Hfr donor 2 min 4 min 6 min Red Yellow Green Blue Black Orange Green Magenta Blue Significance of Hfr strains: •Chromosomal DNA transfer •Allowed mapping of E. coli chromosome Conjugation: Hfr donor Conjugation 10 5/11/2011 The Mobile Gene Pool Core genome Mobile genetic elements plasmids transposons genomic islands (pathogenicity islands) phages E. coli K12, 4.6 x 106 bp E. coli O157:H7, 5.5 x 106 bp The Mobile Gene Pool Example of the implications Resistant to most other antibiotics 11