Transcript Microbial Genetics

Microbial Genetics
DNA is the Genetic Material
• Griffiths
• Avery et al.
DNA: The Genetic Material
Central Dogma
DNA Replication
• Semiconservative
• 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
Transformation
Transduction
Conjugation
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