1. Genetic Transfer and Recombination in Bacteria

2. (a) Cell Types
Procaryotic cell
Eucaryotic cell

3. Genetic Transfer and Recombination in Bacteria
Genetic Transfer is a process whereby genetic material from one bacterium ( donor cell ) is transferred to another bacterium (recipient cell ) .
Like sexual reproduction in eukaryotes, genetic transfer in bacteria is thought to enhance the genetic diversity of bacterial species .
For example, a bacterial cell carrying a gene that provides antibiotic resistance may transfer this gene to another bacterial cell, allowing that bacterial cell to survive exposure to the antibiotic . Figure 1

5. In bacteria there are three different mechanism for transfer of genetic material :
1- Transformation
2- Transduction
3- Conjugation as in ( figure 2 a and b) and ( table 1 )

6. Figure 2-a

7. Figure 2-b

8. 1- Transformation :
The recipient cell takes up free DNA fragment released from donor cell . Transformation known to occur naturally and also used in genetic engineering in recombinant DNA study . and example of genes transferred by transformation the genes for polysaccharide capsule .
Transformation Steps :
1- Donor DNA fragments binds to a cell surface receptor . (figure 3)
2- An extracellular endonuclease cuts the DNA into smaller fragments .
3- One of the DNA strands is degraded and the other which contains the gene enters the bacterial cell .
4- The DNA strand is incorporated into the bacterial chromosome via homologous recombination ( crossing over ) .

9. Transformation

10. 2- Transduction :
Occur when bacterial genes are carried from a donor cell to a recipient cell by a bacterial virus ( bacteriophage : virus that infect bacteria ) . Facilitating subsequent recombination of the genetic markers of the two cells .
Phage attaches to host cells receptors and injects DNA leaving the capsid outside . Inside the cell, viral DNA can either :
A - Replicate to form phage and lyse the host to release the phage progeny ( process called lytic cycle ) . Or
B - Integrate into the bacterial chromosome ( process called lysogenic cycle ) .
Prophage : the viral DNA that integrates into the bacterial chromosome . ( figure 4 ) .

11. The Lytic and Lysogenic cycles of certain Bacteriophages

13. Temperate phages can follow both cycles , other phages known as Virulent phages can only follow a lytic cycles. ( figure 4 ) .
Some phage progeny released from the lytic may contain host DNA ( transducing phage ) which is transferred into a new host in the next infection cycle . The foreign host DNA can integrate by homologous recombination the process is called Generalized Transduction . Figur 5
The prophage may be exits from the bacterial chromosomes carrying small segment of host genes with it and enter the lytic cycle . Transducing phages infect anew host cells where recombination ( crossing over ) occur , the process is called Specialized Transduction . ( figure 6)

14. Therefore there are two types of transduction :
1- Generalized Transduction :
Each gene of the bacterial chromosome has equal chance to be transferred . ( randomally ) .
2- Sprcialized Transduction :
Only genes adjacent to the prophage attachment site on the bacterial chromosome could be transferred .
Genes transferred by transduction :
Genes of toxins such as ( botulinum, diphtheria , cholera ) , genes of enzymes for sugar fermentation and genes of drug resistance .

15. Generalized Transduction

16. Generalized transduction mediated by bacteriophages

17. Specialized Transduction

18. Specialized Transduction

19. Generalized and Specialized Transduction

20. 3- Conjugation :
Requires direct cell contact and involves the transfer of donor DNA to recipient cells through a conjugation tube that forms between the two cells .

21. Conjugation Steps :
1- F- plasmid carries tra genes which code for the production of a sex pilus ( a protein thread ) . ( figure 9 )
2- When the tip of the sex pilus adhere to the cell wall of another cell, it pulls till the two cell, become bound together .
3- The F- plasmid nicked in one strand, where one parental strand passes to the recipient cell and the other remains in the donor cell .
4- Complementary strands are synthesized in both cells simultaneously during transfer .

22. Conjugation

23. Conjugation—a mechanism by which mobilizable plasmids can be transferred from one bacterium to another
Note conjugation bridge formed between donor and recipient cells

24. Plasmid :is an extrachromosomal DNA molecule that can replicate independently of the main cellular chromosome , plasmid is a circular form of DNA .
Types of Plasmids :
1- F- plasmids : the F factors responcible for DNA transfer during conjugation .
2- R- plasmids : DNA molecules carrying genes for resistance to various antibiotics and bacterial drugs . ( figure 6 )
3- Col – plasmids : plasmids that code for proteins called colicins which kill sensitive E.coli cells . All known plasmids are circular molecule of DNA .

25. R- plasmid : DNA molecules carrying genes for resistance to various antibiotics and bacterial drugs

26. Genes transferred by Conjugation :
Genes for drug resistance , resistance to metals , toxins production, enzymes, adherence molecules , degredation of toxic substances , uptake of iron .

27. Some bacteria may also possess Transposons or Jumping genes:
that means genes or DNA segment that moves to another chromosome .

29. DNA Transfer in Bacteria
DNA Trransfer in Bacteria
DNA Transfer in Bacteria
transformation
transduction
conjugation

30. Generalized transduction mediated by bacteriophages

31. for your attention
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