NAJRAN UNIVERSITY College of Medicine NAJRAN UNIVERSITY College of Medicine Microbiology &Immunology Course Lecture No. 6 Microbiology &Immunology Course Lecture No. 6 By Dr. Ahmed Morad Asaad Associate Professor of Microbiology Dr. Ahmed Morad Asaad Associate Professor of Microbiology

II- 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

Genetic transfer Bacterial DNA may be transferred within or between bacterial cells. A. Transfer of DNA within bacterial cells: Transposition: Transposons or jumping genes can move from one site in a DNA molecule to other target chromosomal or plasmid sites in, the same or a different DNA molecule. This process is termed transposition and it results in insertion or deletion mutations.

B. Transfer of DNA between bacterial cells: Bacterial DNA may be transferred between bacterial cells by three mechanisms: transformation, transduction, and 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

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.

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

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

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)

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

Recombinant DNA technique: 1- Chromosomal DNA is extracted and cleaved by Restriction endonuclease which cut at specific sites to separate the required fragment containing the required gene (insert) 2- The vector (e.g., plasmid) is cleaved by the same step 3- The insert + vector are mixed under certain conditions. This results in recombinant plasmid = plasmid+insert 4- By transformation, the recombinant plasmid is introduced into a suitable host (bacteria or yeast cell) which can replicate autonomousely

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)