BACTERIAL GENETICS

1. BACTERIAL GENETICS Dr. Neha

2. Bacterial genetics • Deals with study of heredity and gene variations in bacteria. • All hereditary characters encoded on their DNA in chromosome as well as extra-chromosomal.

3. Bacterial DNA • Single haploid chromosome • Super coiled • Circular • Double stranded DNA • Measures around 1 mm in length • Lacks histone proteins

4. Structure of DNA • Watson and crick model • Two strands • Each strand has 3 parts • Backbone of deoxyribose sugar a d phosphate group • Nitrogenous bases- A,G,T,C. • Hydrogen bonds • In a DNA molecule, A=T and G=C

5. DNA replication • In a prokaryote, DNA replication is similar o an eukaryote with some differences • Can occur by two mechanisms: • Bidirectional Replication • Rolling circle Mechanism

6. Origin of Replication

7. Replication in both directions

8. Replication Forks move bidirectionly until they meet

9. Genetically identical daughter cells (clones)

10. Bacterial RNA • Structurally similar to DNA except.. • Sugar- ribose • Nitrogen base, uracil instead of thymine • 3 types of RNA..mRNA, rRNA, tRNA. • Protein synthesis

11. Polypeptide synthesis • Chromosome • DNA • Gene • Genetic code • Exons and Introns

12. Genetic code • Codon – sequence of nucleotide bases present on mRNA • Stores information of AA synthesis • Nirenberg and Khorana • Sense codon • Non-sense codon • Start codon • Anticodon

13. Transcription and Translation • Segment of DNA---RNA • DNA and mRNA are complementary to each other • mRNA---decoded by ribosome • Produce specific AA chain or polypeptide

14. Has 4 phases: • Initiation • Elongation • Translocation • Termination

15. Plasmid • Extra-chromosomal • ds circular DNA • Exists in free state • Cytoplasm of bacteria and some yeast. • It is not essential for life • Multiple copies • Independent replication • Episomes • Curing . • Plasmids as vectors

16. Classification of plasmids • Based on ability to perform conjugation • Conjugative • Non conjugative • Based on compatibility between plasmids • Based on functions: • Fertility or F- plasmids • Resistance or R plasmids • Col plasmids • Virulence plasmids • Metabolic plasmids

17. Bacterial variation • Phenotypic variation • Genotypic variation • How does bacteria acquire these variations?

18. Mutation • Random • Undirected • Heritable variation • Caused by alteration in the nucleotide sequence • At some point of the DNA of the cell.

19. Types of mutations • Point mutaions: • Transition • Transversion • Silent mutation • Neutral mutation • Missense mutation • Nonsense mutation • Frame shift mutation

20. Reverse mutation: • True reversion • Equivalent reversion • Suppressor mutation

21. Mutations can be • Spontaneous • induced

22. Detection of mutants

23. Mechanisms of gene transfer • Vertical transmission: • From parent to child. • Horizontal transmission: • From one bacterium to another • Transformation • Transduction • Lysogenic conversion • Conjugation

24. Transformation • Process of random uptake of naked or free DNA fragment and its incorporation in bacterial chromosome in a heritable form. • Mechanism: • Lyse---release dsDNA----if competent----taken up by the bacteria present in surrounding. • Well demonstrated through the Griffith’s experiment.

25. Transformation • involves the uptake and assimilation of naked DNA • released • common steps: • binding of exogenous DNA of the cell surface •  • transport of DNA into the cell •  • combination with the resident genome

27. Transduction • Transfer of a portion of DNA from one bacterium to another by a bacteriophage i.e. viruses which parasitize bacteria. • Can transfer episome and plasmid genes as well.

29. Transduction is of 2 types: • Generalised- involves any segment of the donor DNA at random • Restricted – specific bacteriophagetransduces only a particular genetic trait. • Bacteriophages have 2 types of life cycle: • Lytic cycle • Lysogenic cycle

31. Conjugation • Transfer of genetic material from one bacteria to another by mating or contact with each other and forming the conjugation tube. • F+ --- Donor or Male bacterium • F- ---- Recipient or Female bacterium • Donor contains the fertility factor which carries genes for formation of sex pilus.

36. Conjugation plays an important role in transfer of antimicrobial resistance among bacteria. • R Factor = RTF + r determinants

37. Bacterial recombination • General: • Homologus DNA • Reciprocal general recombination • Non reciprocal general reombination • Site specific recombination: integration of DNA into bacterial chromosome is site specific.

38. Transposons • Intracellular transfer between • Chromosome to chromosome • Plasmid to plasmid • Chromosome to plasmid & vice versa • Jumping genes or Mobile genetic elements • Process of transfer of transposons k/as transposition. • 2 types: • Insertion sequence • Composite transposons

39. Genetic engineering • Deliberate modification of organism’s genetic information by altering its nucleic acid genome • Recombinant DNA technology • Gene for desired protein is isolated from an organism • It is inserted in a suitable vector ---transferred to bacteria • Cloning of bacteria ----large quantity of desired protein

40. Vector • Small piece of DNA • Foreign DNA can be inserted and maintained • Used for cloning purpose • 4 types of vectors: • Plasmids • Bacteriophages • Cosmids • Artificial chromosomes

41. Applications • Production of vaccines • Production of antigens • Production of proteins used in therapy • Transgenic animals • Gene therapy

42. Molecular genetics

43. Nucleic acid probes • Blotting techniques • Amplification techniques • Non amplification techniques