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bacterial genetics.pptx

  1. 1. Bacterial Genetics Learning the Basics 1
  2. 2. Genetics Guide Life 2
  3. 3. Understanding Genetics We resemble and differ because of Genetic configurations Parents - Son - Daughter, how they resemble each other. They breed true from Generation to Generation But vary in small proportions in progeny. Bacteria too obey the laws of Genetics 4
  4. 4. Beginning of Bacterial Genetics 4 • The principles of Genetics were applied to bacteria and viruses • Advances in Genetic process also of lead to fundamental advances in Biology and Biochemistry. A Birth of New Branch of Science Molecular Biology
  5. 5. 5 DNA ( Deoxyribonucleic Acid ) • DNA is composed of Many Units of Adenine – Thymine A – T Guanine – Cytosine G - C A+ T G+C proportion differ for each species DNA replicates first unwinding at one end to form a fork Each strand of fork acting as template for the synthesis of complementary strand
  6. 6. DNA • A DNA molecule is composed of two chains of Nucleotides wound together in the form of a Double Helix • Each chain has back bone of Deoxyribose and Phosphates residues arranged alternatively 6
  7. 7. Structure of DNA • Attached to each Deoxyribose and phosphate residues arranged alternatively • Attached to each Deoxyribose are of four nitrogen bases • Purines - Adenine, Guanine • Pyramidine Thymidine and Cytosine 7
  8. 8. 8 How RNA differs from DNA • RNA contains - Sugar Ribose instead of Deoxyribose • Uracil is present instead of Thymine
  9. 9. 9 Knowledge on DNA lead to advances in Molecular Biology • Central dogma of Life – Deoxyribonucleic acid • DNA carries the Genetic information • DNA is transcribed to RNA –Proteins-Enzymes DNA is a store house of Protein synthesis DNA acts a Template for synthesis of mRNA  Virus differs from other as they contains either DNA or RNA
  10. 10. What is a Gene • Gene is a sequence of DNA carrying codons specifying for particular polypeptide. • DNA contains many Genes ( A combinations of hundreds and thousands of Nucleotides ) 10
  11. 11. Bacterial Chromosome • Contains a Double stranded molecules of DNA arranged in circular form. • Length 1,ooo microns. • Bacterial DNA contains about 4,000kilobases • I kb = 1000 base pairs ( A-T ) ( G-C) • Humans have about 3,000 kb pairs. 11
  12. 12. 20 Extra chromosomal Genetic Elements Bacteria posses Extra chromosomal genetic elements Not Essential for survival of Bacteria But makes the Bacteria Resistant to antibiotics, and makes them survive Able to produce toxins
  13. 13. Plasmids • Plasmids are circular DNA molecules present in the cytoplasm of the Bacteria • Capable of Autonomous replication • Can transfer genes from one cell to other • Act as vectors in Genetic engineering. • Can also present in Yeasts 13
  14. 14. Plasmid ( Blue ) 14
  15. 15. 15 Plasmids • Plasmid seem to be ubiquitous in bacteria, May encode genetic information for properties 1 Resistance to Antibiotics 2 Bacteriocins production 3 Enterotoxin production 4 Enhanced pathogen city 5 Reduced Sensitivity to mutagens 6 Degrade complex organic molecules
  16. 16. Plasmids • Can be integrated with Chromosomal DNA • Episomes - Integrated form of plasmid with DNA 16
  17. 17. Potentials of Plasmids • Plasmids can be self transmissible and Non transmissible • Transfers the Sex and Drug resistance with the help of restriction endonucleases 17
  18. 18. 18 Principles of Genotypic variations • Mutations • Genotypic by transfer of genes Transformation Transduction Conjugation Transposons
  19. 19. Mutations in Bacteria 19 • Bacteria Multiply by asexual binary fission • Altered Nucleotide sequence expresses new or altered characteristics • Selective value to the organism • Evolutionary value • Acquires Antibiotic resistance grows in body without inhibition • Become a prominent organism • Phenotypic variation occurs when genes changes in response to the environment but reversible.
  20. 20. The three bacterial sexual processes – 1. Conjugation: direct transfer of DNA from one bacterial cell to another. –2. Transduction: use of a Bacteriophages (bacterial virus) to transfer DNA between cells. –3. Transformation: naked DNA is taken up from the environment by bacterial cells 44
  21. 21. What is Transformation • Transformation is defined as transfer of Genetic information through the activity of DNA • Griffith experiment Mice injected with Live non capsulated ( R ) Pneumococci with heat killed capsulated (S) Pneumococci Lead to death of Mice with isolation of Live capsulated Pneumococci It means that some factor from Dead pneumococci transferred to live non pathogenic Pneumococci 47
  22. 22. Griffith Phenomenon 22
  23. 23. Demonstration of transformation Avery, MacLeod, and McCarty (1944) 23
  24. 24. Transduction • Transduction is defined as transfer of portion of DNA from one bacteria to another by Bacteriophages, is known as Transduction 51
  25. 25. DNA transfer through Bacteriophages • When the Phage particle infects another bacteria DNA transfer is effected and the recipient cell acquires new characters coded by donor DNA 52
  26. 26. Conjugation • A process by which a Donor cell or male cell makes contact with another cell, the recipient or Female cell. • DNA is directly transferable • Plasmid Carry genetic information necessary for conjugation to occur. • Only cell that contain such plasmids can act as donor. the cell lacking a corresponding plasmid act as recipient. • Requires direct contact between donor and recipient 56
  27. 27. Conjugation • The ability to conjugate is conferred by the F plasmid. A plasmid is a small circle of DNA that replicates independently of the chromosome. Bacterial cells that contain an F plasmid are called “F+”. Bacteria that don’t have an F plasmids called “F-” 57
  28. 28. Conjugation - Transferring genes with plasmids • Plasmids mediating conjugation carry genes coding for properties, of 1-2 microns long protein appendage termed Pilus on the Donor cell 28
  29. 29. Conjugation 60