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Microbial Genetics
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DNA is the Genetic Material• Griffiths• Avery et al.
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DNA: The Genetic Material
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Central Dogma
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DNA Replication• Semi-
conservative• Fidelity of
information transfer to new strands depends on base-pairing of nucleotides
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Transcription• Synthesis of mRNA strand off of a DNA template• mRNA carries the genetic information
(message) to the ribosomes• Only one strand of DNA is used as a template
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RNA• Three types
– mRNA– rRNA– tRNA
• All three molecules needed for protein synthesis (translation)
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Transfer RNA (tRNA)• “Clover-leaf”
shaped molecule• Functions to
transport amino acids to ribosomes and insert them into proteins
• One end interacts with aa; other with mRNA
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Translation
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The Genetic Code
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Control of Genetic Expression
Operons
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The Lac Operon
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Genetic Exchange in Bacteria
TransformationTransductionConjugation
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Genetic Exchange• Bacteria have three different ways
in which “new”, donor genetic material can be acquired
• Once the DNA gets into the cell it may be– Degraded– Incorporated into the genome– Persist independently
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Transformation• Remember Avery et al.• Transfer and incorporation of a
piece of naked DNA
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Transduction• DNA is carried by a phage• Defective phages and lysogeny
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Conjugation• Physical contact (via a sex pilus)
between two cells• Transfer of a piece of DNA through
the pilus• Useful in mapping bacterial
chromosome• Conjugation and bacterial sex• F+ , F-, and Hfr strains
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Plasmids• Extrachromosomal pieces of DNA• Usually carry nonessential, but
important traits– Resistance plasmids– Degradative plasmids– Cryptic plasmids
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Applications of Molecular Genetics
Detection and Identification of Microorganisms
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Molecular Probes• If the sequence of an organism is
known (or a portion of the sequence), it is possible to design a molecular probe for that sequence.
• Amplification of a sequence (probe): PCR
• Direct detection: FISH probes• Other molecular methods
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FISH Probes