NAJRAN UNIVERSITY College of Applied Medical Sciences

1. NAJRAN UNIVERSITY College of Applied Medical Sciences General Microbiology Course Lecture No. 8 By Dr. Ahmed MoradAsaad Associate Professor of Microbiology

2. Genotypic variations: • These are permanent (irreversible) variations, which are heritable, i.e. they will be transmitted among generations. They may be due to: • 1-Mutation • 2-Gene transfer: • *-Transfer of DNA within bacterial cell (transposition) • *-Transfer of DNA between bacterial cells (transformation, transduction and conjugation)

3. Gene transfer Transfer of bacterial DNA within or between bacterial cells • Transfer of DNA within bacterial cells • Transposition: • Movement of transposons from one site in a DNA molecule to other target chromosomal or plasmid sites. • It results in insertion or deletion mutations secondary to alternative excision/insertion of a transposon from one DNA locus to another

4. Transfer of bacterial DNA between bacterial cells By Transformation – transduction - conjugation • Transformation: • The transfer of DNA from one cell to another by either of 2 mechanisms: • 1- In nature, dying bacteria may release their DNA which may be taken by another cells • 2- In the lab, DNA may be extracted from one bacterial cell into another one

6. Transduction Transfer of bacterial DNA by means of a bacterial virus (bacteriophage). 2 types of transduction: generalized and specialized • Generalized transduction: • This occurs when the bacterial virus carries a segment from any part of the bacterial chromosome. This occurs because cell DNA is fragmented after phage infection and a piece of DNA is incorporated into the virus.

7. Specialized transduction: • This occurs when the bacterial virus that has integrated into the cell DNA is excised and carries with it an adjacent part of the cell DNA

9. Conjugation: • 1- It is the mating of 2 bacterial cells during which DNA is transferred from the donor to recipient cell. • 2- The mating process is controlled by F (fertility) plasmid (F factor) which carries genes for synthesis of pilin and form sex pilus. • 3- Mating begins when the sex pilus of donor male bacteria carrying F factor (F+) attach to to recipient female bacteria (F-). • 4- Cleavage of F factor DNA: one strand to recipient cell. • The process is completed by synthesis of a complementary strand in each cell

11. Plasmid: • 1- Extrachromosomal small circular double-stranded DNA. • 2- Dispensable • 3- Carry genetic informations that confer new phenotypic properties: • *- Antibiotic resistance • *- Sex pillus (F pillus) • *- Virulence factors • *- Bacteriocin • *- Enzymes

12. Genetic engineering • *- A method to isolate genes coding for certain properties and join them together to form new combinations. • *- Also called genetic recombination, recombinant DNA technology, DNA cloning. • *- Major 3 steps (It requires): • 1- Separation of required gene (by restriction endonuclease). • 2- Carrying this gene by a vector • 3- Introducing the gene into a host cell (by transformation)

13. Restriction endonucleases: • *- Enzymes from bacteria and fungi that can recognize and cut DNA fragments (genes) at specific sites • Vectors: • 1- Plasmids • 2- Bacteriophage • 3- Cosmids: circular double-stranded DNA molecule constructed from plasmid DNA+phage DNA. They carry large genes • 4- Retroviruses and adenoviruses

14. Applications of recombinant DNA technology: • 1- Extensive chromosomal and genes studies • 2- Preparation of probes for diagnostic purposes • 3- Production of proteins of medical importance (large amount + low coast) • 4- production of recombinant vaccines • 5- Gene therapy (virus vectors)