Bacterial Genetics and Gene Transfer PDF

Bacterial Genetics and gene transfer 1  Lecture ILOs By the end of this chapter, students should be able to:  Identify bacterial genome  Describe bacteriophage, its structure, differentiate between its types  Describe plasmids, their function...

Bacterial Genetics and gene transfer 1  Lecture ILOs By the end of this chapter, students should be able to:  Identify bacterial genome  Describe bacteriophage, its structure, differentiate between its types  Describe plasmids, their function and classify them.  Compare phenotypic and genotypic variations.  Recognize different methods of gene transfer 2 Bacteriophage 3  Bacteriophage=bacterial virus They are viruses that infect bacteria. consists of a head contain DNA OR RNA + tail+ terminal base plate to which are attached tail fibres Tail fibers function = responsible of attachment to bacterial cells wall receptor 4  Types of Bacteriophage Lytic or Virulent Phage :Phages which can kill the bacterial cell by lysis Lysogenic or Temperate Phage: phages fail to lysis the bacterial cells. Its DNA integrated with the bacterial chromosome and it passes to daughter cells as the bacteria divide. 6  The bacterial genome  is the total set of genes present inside the bacteria include  1- Essentially single circle bacterial chromosome contain essential structure gene 2- Additional genes may be carried or not I. Plasmids extrachromosomal circular DNA I. Bacteriophage DNA 7  Plasmids Extrachromosomal double-stranded, circular DNA Carry genes for non essential genes code non essential bacterial character 8 9  Conjugative = transmissible plasmids F-plasmid=Fertility plasmid= transmissible plasmid contain tra gene that code for formation of sex pilus Bacteria contain F plasmid called F + cell Sex pilus = bridge between bacteria for gene transfer by conjugation 10 Sex Pilus 11  Functions of plasmids - Genes coding for drug resistance of many bacteria are carried on plasmids. - Some plasmids carry genes whose products are the virulence factors (Pilli---Toxins) of some pathogenic organisms. 12 Bacterial Gene Transfer 13 Vertical gene transfer Genetic information passed from bacteria to its (daughters) offspring from generation to another generation = reproduction Horizontal gene transfer Bacteria transfer genetic information form one organism to another in the same generation leading to change in its character  GENE TRANSFER There are 3 types of gene transfer from one bacterium to the other leading to change in its character by 3 methods 1. Transformation: free bacterial DNA in media is taken up by another bacteria May be induced in laboratory 2-Conjugation: bacteria donor contain F plasmid contact to recipient bacteria by sex pilus result in plasmid or part of chromosome can transferred 3-Transduction: Transfer of DNA from bacteria to another by bacteriophage 16  Transformation Naked piece of DNA released from donor bacteria are taken up directly by recipient bacteria. from the surrounding medium. Bad news = DNA is naked and may be destroyed by nuclease 17  Conjugation It is mating of two bacterial cells. F + Bacteria contain F plasmid, which carries the genes (tra gene) that code for formation of sex pilus which bridges between Two bacterial cells. At the end two F+ cell produced If plasmid transferred 18 19 20 Plasmid transfer Conjugation occurs between an F+ cell and an F- cell. Sex pilus, connects the two cells. At the end two F+ cell produced 21 Application of bacterial gene transfere 1-genetic engineering and gene cloning 2-idea about transfer of drug resistance 22 Bacterial Physiology By Prof. azza labeeb Faculty of Medicine Menoufia University  Bacterial reproduction Binary fission: method of bacterial reproduction to increase their number One cell divides into two equal daughter cells similar to the parent cell. Bacterial generation time is the time it  takes for a population of bacteria to double in number. For many common bacteria, the generation time is quite short, 20-60 minutes under optimum conditions Bacterial growth Curve bacteria are inoculated into a liquid nutrient medium and the bacteria are counted at frequent intervals and the results plotted, a characteristic growth curve with four phases is obtained. Bacterial growth Curve: 4 phases  Lag phase: It is the first phase during which no cell division occurs. The bacteria adapt to the new environment by formation of new enzymes and molecules needed for replication. Logarithmic phase: During this phase, rapid cell division occurs and the number of bacterial cells increases steadily by time. The best stage for antibiotic action Rapid grower or slowly grower Stationary phase:  As the nutrients in the medium are exhausted  and toxic products accumulate, the rate of growth decreases. The number of living bacteria remains constant because the number of dying cells equals that of newly formed cells. Decline phase:  As the exhaustion of nutrients and  accumulation of toxic products continues, the death rate exceeds the multiplication rate and the number of living bacteria