Post on 18-Jan-2018
Microbial Genetics
DNA is the Genetic Material• Griffiths• Avery et al.
DNA: The Genetic Material
Central Dogma
DNA Replication• Semi-
conservative• Fidelity of
information transfer to new strands depends on base-pairing of nucleotides
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
RNA• Three types
– mRNA– rRNA– tRNA
• All three molecules needed for protein synthesis (translation)
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
Translation
The Genetic Code
Control of Genetic Expression
Operons
The Lac Operon
Genetic Exchange in Bacteria
TransformationTransductionConjugation
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
Transformation• Remember Avery et al.• Transfer and incorporation of a
piece of naked DNA
Transduction• DNA is carried by a phage• Defective phages and lysogeny
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
Plasmids• Extrachromosomal pieces of DNA• Usually carry nonessential, but
important traits– Resistance plasmids– Degradative plasmids– Cryptic plasmids
Applications of Molecular Genetics
Detection and Identification of Microorganisms
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
FISH Probes