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MICROBIAL GENETICSCHAPTER 7

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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

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DNA Structure

Thymine (T)

Nitrogenous base(A, G, C, or T)

Phosphategroup

3’

5’

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Microbial Genetics Genes

Alleles

Mutations

3 letter code

Genes named by mutations

Single

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Genetic Information Storage DNA/Base sequences

Genetic information transfer

The Central Dogma

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DNA Replication DNA structure

– Double helix

– Antiparallel strand orientation

– Strand unwinding

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DNA Replication

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DNA Polymerase Leading strand synthesis

Lagging strand synthesis

Need for DNA Ligase

Okizaki fragments

Synthesis always 5’ to 3’

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RNA Synthesis RNA Polymerase

Promoter sequences -35 ttattgaat -10 ttaaat 3 RNA types

– rRNA

– mRNA

– tRNA

Also 5’ to 3’

Sigma70 (housekeeping)

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DNA sequencing

http://www.dnalc.org/ddnalc/resources/sangerseq.html

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Gene Complexity Compared Eukaryotic

Prokaryotic

Introns, lots of gene redundancies

No introns, few redundancies

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Genetic Code mRNA codons

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Protein Synthesis tRNA anticodons

Amino acid links

Role of ribosomes

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Protein Synthesis

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Protein Synthesis

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Coupling of Transcription/Translation

Prokaryotic streamlining

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Regulation of Metabolism Feedback Inhibition (Enzymatic)

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Genetic Regulation of Metabolism Enzyme Induction Enzyme Repression

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Genetic Regulation of Metabolism

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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

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Mutations Genotype

Phenotype

Actual allele type

What we see

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Mutation Types Point mutations

– Silent

– Missense

– NonsensePuts in stop codon

Change in DNA, but same AA put in

silent

missense

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Mutation Types Frameshift

Rearrangements

Quite damaging

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Gene Mutations• Frameshift Mutations – shifts

the reading frame of the geneticmessage so that the protein maynot be able to perform itsfunction.– Insertion

• THE FAT CAT ATE THE RAT• THE FAT HCA TAT ETH ERA T

– Deletion• THE FAT CAT ATE THE RAT• TEF ATC ATA TET GER AT

H

H

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Causes of Mutation Spontaneous 10-8

Chemical mutagens

teratogens, mutagens

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Causes of Mutation

Radiation

Thymine dimers

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DNA Repair Light

Repair

Dark Repair

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Mutation Studies

Xeroderma pimentosa = loss of DNA repair

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Ames TestStart with a mutant his gene

Mutagens lead to reversion mutation

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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

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PCR polymerase chain reaction

http://www.maxanim.com/genetics/PCR/PCR.htm

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 growsin hot springs = thermostable