1 microbial genetics chapter 7. 2 microbial genetics heredity bacteria are haploid although some can...
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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