1st Lecture--Conjugation--23.07.19.ppt..

1st Lecture--Conjugation--23.07.19.ppt..

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  MZOOCC 103- Genetics UnitII: Microbial genetics 2. l. Transformation, conjugation, transduction and sexduction in bacteria
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  Bacterial Genetics
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  Why there isneed to study? • There are distinct advantages to use bacteria for genetic engineering • Bacterial culture contains millions of single cells. • Prokaryotic cells contains a single chromosome • Rapid growth • Easy to grow microbes in controlled environment 3
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  Bacterial Recombination • GeneticRecombination is the formation of a new genotype by re assortment of gene following an exchange of genetic material between two different chromosomes having similar genes at corresponding sites. These are called homologous chromosomes • In bacteria genetic recombination results from three type of gene transfer: A. Conjugation- by physical contact B. Transduction- by bacteriaophage C. Transformation- by naked DNA from one cell to other 4
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  • In bacterialrecombination cell do not fuse, but a portion of chromosome is transferred from Donor (Male) to recipient (Female) cells. • General mechanism for bacterial recombination is based on breakage and reunion model. • The donor DNA becomes integrated into the recipient DNA. 5
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  Conjugation 6
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  Plasmids • Many DNAsequences in bacteria are mobile and can be transferred between individuals and among species. • Plasmids are circular DNA molecules that replicate independently of the bacterial chromosome • Plasmids often carry antibiotic resistance genes • Plasmids are used in genetic engineering as gene transfer vectors 7
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  Basic Overview ofConjugation
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  F factor andConjugation • F (fertility) factor is a conjugative plasmid transferred from cell to cell by conjugation • F factor is an episome i.e. genetic element that can insert into chromosome or replicate as circular plasmid • The F plasmid is a low-copy-number plasmid ~100 kb in length, and is present in 1–2 copies per cell • It replicates once per cell cycle and segregates to both daughter cells in cell division
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  F factor andConjugation 10 • Conjugation is a process in which DNA is transferred from bacterial donor, F+ cell to a recipient, F- cell by direct contact. • The transfer is mediated by a tube-like structure called a pilus, formed between the cells, through which the plasmid DNA passes. • Once in contact, conjugation, DNA transfer is unidirectional. The lagging strand template peels away… and is transferred to the recipient. • The leading strand template is replicated in the donor while the lagging strand template is replicated in the recipient… so that both cells wind up with the plasmid.
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  Hfr strains (Highfrequency recombinant ) • F factor can integrate into chromosome via genetic exchange between IS elements present in F and homologous copy located anywhere in bacterial chromosome • Cells with the F plasmid integrated into the bacterial chromosome are known as Hfr cells • When an Hfr cell undergoes conjugation, the process of transfer of the F factor is initiated in the same manner as in an F+ cell • However, because the F factor is part of the bacterial chromosome, transfer from an Hfr cell also includes DNA from the chromosome 11
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  Hfr and Conjugation •Transfer begins within an integrated F factor and proceeds in one direction • A part of F factor is the first DNA transferred, chromosomal genes are transferred next, and the remaining part of F is the last • The conjugating cells usually break apart long before the entire bacterial chromosome is transferred, and the final segment of F is almost never transferred The recipient cell remains F-