Chapter 8 Microbial Genetics

1. Chapter 8Microbial Genetics Biology 1009 Microbiology Johnson-Summer 2003

2. Structure and Function of Genetic Material • 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) • 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. Replication Fork

8. Protein Synthesis • DNA------- mRNA------ protein transcription translation Central Dogma 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. Transcription

11. 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)

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

13. 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

14. Genetic Code

15. 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)

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

21. Normal DNA/Missense Mutation

22. Nonsense Mutation/Frameshift Mutation

23. Genetic Transfer in Bacteria • Genetic transfer-results in genetic variation • Genetic variation-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

24. Transduction by a Bacteriophage

25. Transformation

26. Conjugation in E. coli

27. Conjugation continued…

28. Conjugation continued…