1. Chapter 6Microbial Genetics

2. Structure and Function of Genetic Materials DNA & RNA DNA=deoxyribonucleic acid RNA=ribonucleic acid Basic building blocks: Nucleotides Phosphate group Pentose sugar Nitrogenous base

3. Structure of DNA • Double stranded (double helix) • Chains of nucleotides • 5’ to 3’ (strands are anti-parallel) • Complimentary base pairing • A-T • G-C

4. DNA Structure Phosphate-P Sugar-blue Bases-ATGC

5. DNA Replication • Bacteria have closed, circular DNA • Genome: genetic material in an organism • E. coli • 4 million base pairs • 1 mm long (over 1000 times larger that actual bacterial cell. How it can be put into a cell? • DNA takes up around 10% of cell volume

6. DNA Replication occurs at the replication fork • 5’ to 3 ‘ • DNA helicase-unzips + parental DNA strand that is used as a template • Leading stand (5’ to 3’-continuous) • DNA polymerase-joins growing DNA strand after nucleotides are aligned (complimentary) • Lagging strand (5’ to 3’-not continuous) • RNA polymerase (makes short RNA primer) • DNA polymerase (extends RNA primer then digests RNA primer and replaces it with DNA) • DNA ligase (seals Okazaki fragments-the newly formed DNA fragments)

7. 解旋酶打开DNA双螺旋 Replication Fork 1

8. Protein Synthesis DNA------- mRNA------ protein transcription translation Central Dogma(中心法则) of Molecular Genetics

9. Transcription • One strand of DNA used as a template to make a complimentary strand of mRNA • Promoter/RNA polymerase/termination site/5’ to 3’ • Ways in which RNA & DNA differ: • RNA is ss • RNA sugar is ribose • Base pairing-A-U

10. The structure of a bacterial gene I. Single gene transcript Translational end Transcription start site Coding sequence TAA ATG hisG transcript Transcriptional terminator Ribosome binding site/ translational start (ATG) Promoter

11. Multigene bacterial operon Translational end Transcription start site TAA ATG TAA hisG hisH transcript -One promoter, one transcriptional stop; multiple translational starts and stops

12. Transcription

13. Types of RNA • Three types: • mRNA: messenger RNA • Contains 3 bases ( codon) • rRNA: ribosomal RNA • Comprises the 70 S ribosome • tRNA: transfer RNA • Transfers amino acids to ribosomes for protein synthesis • Contains the anticodon (3 base sequence that is complimentary to codon on mRNA)

14. Genetic Code • DNA: triplet code • mRNA: codon (complimentary to triplet code of DNA) • tRNA: anticodon (complimentary to codon)

15. Genetic Code • Codons: code for the production of a specific amino acid • 20 amino acids • 3 base code • Degenerative: more than 1 codon codes for an amino acid • Universal: in all living organisms

16. Genetic Code

17. Translation • Three parts: • Initiation-start codon (AUG) • Elongation-ribosome moves along mRNA • Termination: stop codon reached/polypeptide released and new protein forms • rRNA=subunits that form the 70 S ribosomes (protein synthesis occurs here) • tRNA=transfers amino acids to ribosomes for protein synthesis)

18. Translation

19. Translation

20. Translation

21. Translation

22. Mutations • Changes in base sequence of DNA/lethal and inheritable • Can be: • Harmful • Lethal • Helpful • Silent

23. Normal DNA/Missense Mutation

24. Nonsense Mutation/Frameshift Mutation

25. Genetic Transfer in Bacteria • Genetic transfer results in genetic variation • Genetic variation is needed for evolution • Three ways: • Transformation: genes transferred from one bacterium to another as “naked” DNA • Conjugation: plasmids transferred 1 bacteria to another via a pilus • Transduction: DNA transferred from 1 bacteria to another by a virus

26. Transduction by a bacteriophage

27. Generalized Transduction • Infection of Donor • Phage replication and degradation of host DNA • Assembly of phages particles • Release of phage • Infection of recipient • Homologous recombination Potentially any donor gene can be transferred

28. Transformation • Steps • Uptake of DNA • Gram + • Gram - • Recombination • Legitimate, homologous or general • recA, recB and recC genes • Significance • Phase variation in Neiseseria • Recombinant DNA technology

29. Transformation

30. Conjugation in E. coli

31. Conjugation continued…

32. Conjugation continued…