recombination in bacteria
TRANSCRIPT
Recombination in bacteria
By. Pandya Dilip
Cug/2014/1078
Gene transfer in becteria
• transfer genetic material from one becteria to another becteria
• In bacteria genetic transfer can happen three ways:– Transduction– Conjugation– transformation
Transduction
Transduction
• Definition: gene transfer from a donor to a recipient by way of a bacteriophage
• Discover by lederberg & zinder in 1951
• Bacteriophage (phage): A virus that infects bcteria
Bacteriophage - structure
Types of Bacteriophage
• Bacteriophages have been classified into two types on the basis of their interaction with a bactria cell.
1. Virulent phages. 2. Temperate phages.
• Virulent – always multiply & lyse the host cell after infection.
• Temperate phage: That have a choice between two life-style after infection.
1.Lytic cycle 2.lysogenic cycle
• 1. Lytic cycle = they reproduce & lyse their host cell just like virulent phages.
• Lysogenic cycle = their chromosome are integrated in to the chromosome of the host.
Transduction
• Types of transduction1. Generalized - Transduction in
which potentially any donor bacterial gene can be transferred.
2. Specialized- Transduction in which only certain donor genes can be transferred
Generalized transduction
• Starts with the LYTIC CYCLE where a T- even phage infects E. coli killing the host cell, and synthesizing >100 copies of itself.
• The T-even phage randomly packages bacterial DNA in a few defective phages.
• Once a T – even phage infects another E. coli, this genetic information can be recombined into the host cell without causing the lytic cycle.
• New genetic information is thereby transduced from one bacteria to another.
Generalized Transduction
Specialized Transduction
• In specialized transducing particle carries only specific portions of the bacterial genome.
• Specialized transduction by a temperate bacteriophages which chromosome are able to integrate at a specific attachment site on host chromosome.
• Phages chromosome & bacterial chromosome is a attach specific attachment site by a covalently in prophages.
• The gal transducing phage (lambda) makes ~ 2,000 copies of itself with the gal gene, and infects other E.coli.
• When gal integrates into the nucleoid of other E. coli, it may provide these bacteria with a new capacity to metabolize galactose.
• The best-studied example of specialized transduction is the lambda phage. The lambda genome inserts into the host chromosome at specific locations known as attachment or att sites.
• The phage att sites and bacterial att sites are similar and can complex with each other.
conjugation
• Bacterial conjugation is the transfer of genetic material (plasmid) between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells.
• Discovered in 1946 by Joshua Lederberg and Edward Tatum,
BACTERIA A BACTERIA B
Transfer of genetic material from bactria A to bacteria B by physical
contact is called conjugation.
Who is donor ?
F plasmid absent donor recipient F + F- Male cell femal cell
What happen during conjugation
What is Hfr cell?
• When F factor/ plasmid exists in an integrated state with the host chromosome
Hfr conjugation