Microbial Genetics

1. Microbial Genetics Chapter 8

2. Structure and Function of Genetic Material • DNA & RNA • DNA • deoxyribonucleic acid • RNA • ribonucleic acid • Nucleotides • Phosphate group • Pentose sugar • Nitrogenous base

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

6. DNA Replication • Bacteria have only 1 chromosome (ccDNA) • E. coli • about 4 million base pairs • 1 mm long (1000 times longer than the cell) • DNA takes up only about 10 % of cells volume

7. E. coli DNA 1u 1,360u 1ft. 1,360 ft.

8. DNA Replication occurs at the Replication Fork (5’ to 3’) • DNA Helicase • 1. Leading Strand ( 5’ to 3’ ) • DNA Polymerase • 2. Lagging Strand ( 5’ to 3’) • RNA Polymerase (RNA Primer) • DNA Polymerase (extends primer and digests RNA) • DNA Ligase • Okazaki Fragments

10. Bidirectional replication • Origin of replication • Termination site

11. Protein Synthesis • DNA mRNA Protein • Transcription Translation • Central Dogma of Molecular Genetics

12. Transcription • One strand of DNA is used as a template to form a complimentary strand of mRNA • mRNA ----> messenger RNA

13. Transcription • 3 ways RNA differs from DNA • Promoter • RNA Polymerase • Termination Site • 5’ to 3’

15. 3 Types of RNA • 1. mRNA • Contains the codons • 2. rRNA • Ribosomes (70S) • 3. tRNA • Transfer amino acids to the ribosomes for protein synthesis • Anti-codon

16. DNA mRNA tRNA Triplet code codons anticodons Genetic Code

17. Genetic Code • Codons code for a specific amino acid • 20 amino acids • 3 base code - 4 bases ( A,U,G,C ) • 64 possible combinations ( 43) • Amino acids are coded for by more than one codon • Genetic Code is Degenerative • Genetic Code is Universal

19. Translation • rRNA • ribosomal RNA (forms the ribosomes) (70S) • tRNA • transfer RNA (transfers amino acids to the ribosomes for protein synthesis) • anticodon • 3 base sequence that is complimentary to the codon on mRNA

24. Regulation of Gene Expression • All Genes are not always being expressed • Genes turned on all the time - Constitutive • Other genes can be regulated: • Turned On • Turned Off

25. lac operon • Lac - Lactose (dissacharide) • Glucose and Galactose • operon - series of structural genes all under the control of a Regulatory Gene • lac operon is normally turned off • lac operon is an Inducible operon

26. Tryptophan operon • Tryptophan - amino acid • operon - series of structural genes all under the control of a Regulatory Gene • Tryptophan operon is normally turned on • Tryptophan operon is a repressible operon

27. Mutations - a change in the base sequence of DNA • Mutations can be: • 1. Harmful • 2. Lethal • 3. Beneficial • 4. Silent (neutral) • UUU - Phe • UUC - Phe

28. Types of Mutations Normal DNA

29. Base Substitution Mutation C Missense Mutation

30. Base Substitution Mutation T Nonsense Mutation

31. Frame Shift Mutation • ATG CAT GCA TGC ATT TCC TGC TTA AAA • 1. Addition Mutation • AAT GCA TGC ATG CAT TTT CCT GCT TAA • Reading Frame is Shifted • 2. Deletion Mutation • TGC ATG CAT GCA TTT CCT GCT TAA • Reading Frame is Shifted

32. Genetic Transfer in Bacteria • Genetic Transfer - results in Genetic Variation • Genetic Variation - is needed for Evolution • 3 Ways Genetic Transfer can occur in Bacteria • 1. Transformation • 2. Cunjugation • 3. Transduction

33. Transformation • Genes are transferred from one bacterium to another as “naked” DNA • Frederick Griffith (1928)

34. Griffith’s Experiment • 2 Strains of Streptococcus pneumoniae • 1. Virulent strain with a capsule - Pneumonia • 2. Avirulent strain without a capsule - no disease

35. Griffith’s Experiment

36. Griffith’s Experiment

37. Griffith’s Experiment

38. Griffith’s Experiment

40. Conjugation One bacterium passes some DNA (in a plasmid) to another bacterium

41. Transduction • DNA is transferred from one bacterium to another by a virus • Bacteriophage • virus that only infects bacteria