1 MICROBIAL GENETICS CHAPTER 7

2 Microbial Genetics Heredity bacteria are haploid although some can be merodiploid while they are dividing. Because of their fast generation time, mutations can become fixed quicker. They possess mechanisms of repair and recombination to keep mutations at an optimal level. Chromosomes for most bacteria are circular in nature. They replicated via a bidirectional eyelet. The start site is calle “ori” 890 genomes sequenced E coli 4.5 megabases

3 DNA Structure Sugar (deoxyribose) Thymine (T) Nitrogenous base (A, G, C, or T) Phosphate group 3’ 5’

4 Microbial Genetics Genes Alleles Mutations 3 letter code Genes named by mutations Single

5 Genetic Information Storage DNA/Base sequences Genetic information transfer The Central Dogma

6 DNA Replication DNA structure –Double helix –Antiparallel strand orientation –Strand unwinding

7 DNA Replication

8 DNA Polymerase Leading strand synthesis Lagging strand synthesis Need for DNA Ligase Okizaki fragments Synthesis always 5’ to 3’

9 RNA Synthesis RNA Polymerase Promoter sequences -35 ttattgaat -10 ttaaat 3 RNA types –rRNA –mRNA –tRNA Also 5’ to 3’ Sigma70 (housekeeping)

10 DNA sequencing

11 Gene Complexity Compared Eukaryotic Prokaryotic Introns, lots of gene redundancies No introns, few redundancies

12 Genetic Code mRNA codons

13 Protein Synthesis tRNA anticodons Amino acid links Role of ribosomes

14 Protein Synthesis

15 Protein Synthesis

16 Coupling of Transcription/Translation Prokaryotic streamlining

17 Regulation of Metabolism Feedback Inhibition (Enzymatic)

18 Genetic Regulation of Metabolism Enzyme Induction Enzyme Repression

19 Genetic Regulation of Metabolism

20 Catabolite repression The Lac operon has multiple forms of regulation previously discussed derepression and Lac will not be transcribed as long as there is glucose glucose = low cAMP CAP is positive activator, but only when bound to cAMP

21 Mutations Genotype Phenotype Actual allele type What we see

22 Mutation Types Point mutations –Silent –Missense –Nonsense Puts in stop codon Change in DNA, but same AA put in silent missense

23 Mutation Types Frameshift Rearrangements Quite damaging

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25 Causes of Mutation Spontaneous Chemical mutagens teratogens, mutagens

26 Causes of Mutation Radiation Thymine dimers

27 DNA Repair Light Repair Dark Repair

28 Mutation Studies Xeroderma pimentosa = loss of DNA repair

29 Ames Test Start with a mutant his gene Mutagens lead to reversion mutation

30 The Ames test is a biological assay to assess the mutagenic potential of chemical compounds. A positive test indicates that the chemical might act as a carcinogen (although a number of false-positives and false-negatives are known). As cancer is often linked to DNA damage, the test also serves as a quick assay to estimate the carcinogenic potential of a compound since it is difficult to ascertain whether standard carcinogen assays on rodents were successful. The procedure is described in a series of papers from the early 1970s by Bruce Ames and his group at the University of California, Berkeley. Cheap test but sometimes overly interpreted

31 PCR polymerase chain reaction How to make lots of DNA copies from a little DNA Use sequence specific primers and Taq polymerase Taq polymerase is from Thermus aquaticus which grows in hot springs = thermostable