Learning Outcomes To compare the mechanism of genetic recombination in bacteria To describe the function of plasmids and transposons refers to the rearrangement of DNA from separate groups of genes usually involves DNA from different organisms exchange between 2 DNA to form new combinations of genes in a chromosome contributes to genetic diversity in eukaryotes the transfer can be done as a part of the sexual cycle in prokaryotes in several ways In all of the mechanism, transferred involved; donor cell- that give a portion of its total DNA recipient cell- that received a portion of DNA from donor cell parts of donor DNA is incorporated into the recipient DNA when some of the donors DNA has been integrated into the recipients DNA, the resultant cell is called a recombinant Transformation gene transfer from one bacterium to another as naked DNA in solution Transduction donor DNA transfer is mediated by a virus Conjugation transfer involve cell to cell contact conjugative plasmid is the donor cell genes are transferred from donor to recipient bacteria as naked DNA in solution refer to Griffiths expt used Streptococcus pneumoniae two strain; virulent (pathogenic)-capsule-cause pneumonia avirulent- lack capsule-no pneumonia disease DNA from virulent can enter avirulent, changing avirulent strain genetically so that their progeny were encapsulated--become virulent i). DNA transformation: in vivo experiment Mice are injected either with Type R, non- virulent Streptococcus or with heat-killed, virulent Type S cells. The mice are healthy. X Mice are injected with both Type R, non- virulent and heat-killed, Type S Streptococcus DNA carrying genes from the virulent, heat-killed cells transforms the non-virulent bacterial cells, making them lethal to the mice DNA transformation: in vitro experiment Type R cellsType R colonies Type S cellsType S colonies Mixture of Type R and Type S colonies Type R cells + DNA from Type S cells Process by which free DNA is incorporated into a recipient cell and bring about genetic change--recombinant cell work best when the donor and recipient cells are closely related recipient cell have to physiological state to take up the donor DNA--be competent Competence- alterations in the cell wall that make it permeable to large NDA molecules some bacteria are naturally competent but some have to undergo treatment to make it competent Genetic transformation in bacteria DNA is transferred from donor to recipient via a bacteriophage bacterial DNA is incorporated into the bacteriophage generalized transduction: any bacterial genes are transferred specialized transduction: specific regions of DNA are transferred Generalized transduction Specialized Transduction self-replicating covalently closed circular DNA molecules that are usually not essential for survival several types of plasmids dissimilation plasmid Code for enzymes for catabolism of certain unusual sugars and hydrocarbon Conjugative plasmid- F factor-carries genes for sex pili and transfer of plasmid R factors (resistant factors) Significant medical importance Carry genes that confer upon their host cell resistance to antibiotics, heavy metals, or cellular toxins requires contact between donor and recipient cells mediated by plasmid (a circular DNA that replicate independently from cell chromosome) differ from transformation; cell to cell contact opposite mating type; donor cell carry plasmid, recipient cell do not gram -negative- used pili for contact (sex pili) gram-positive cell- sticky surface molecule 2 kinds; Plasmid transfer Chromosome transfer Plasmid transfer F + donor contains F plasmid F - recipient cells do not contain F plasmid sex pilus is formed one strand of DNA is transferred into the recipient cell from the donor cell F - become F + Chromosome transfer when F plasmid is integrated into the chromosome, an Hfr cell is formed Hfr = high frequency recombinant during conjugation, an Hfr cell can transfer chromosomal DNA into the recipient cell (F - ) usually the chromosome breaks before it is fully transferred F - become recombinant F - cell small segments of DNA that can move from one region of a chromosome to another region of the same chromosome or to a different chromosome or DNA molecule found in chromosomes, plasmids, viruses simple to complex structures can carry any type of gene, including antibiotic resistance genes cause mutations increase (or decrease) the amount of DNA in the genome. There are three distinct types: Class II Transposons consisting only of DNA that moves directly from place to place. Class III Transposons; also known as Miniature Inverted-repeats Transposable Elements or MITEs. Class I-Retrotransposons thatRetrotransposons 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.reverse transcriptase Transposons in Bacteria insertion sequence-simplest transposon- carry a genes for transposase complex transposon - carry other genes (code for antibiotic) in addition to transposase genes