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