1. Microbial Models: The Genetics of Viruses and Bacteria
Understanding of microbial models have further advanced other areas of biology (ex. Genetic Engineering)

2. Viral structure Virus: (Latin = poison)
Infectious particles consisting of a nucleic acid (DNA or RNA) in a protein coat (capsid)
Bacteriophages (phages)

3. Host range: Infection of a limited range of host cells
Receptor molecules on the surface of cells dictate ability for infection
Once inside the cell, the nucleic acid follows one of two paths:
Lytic
Lysogenic

4. Viral reproduction: Lytic Cycle
Viral reproduction: Lytic Cycle
Immediately takes over the host cell and begins making new viruses.
The lytic cycle: attachment 2- injection 3- hydrolyzation 4- assembly 5- release
Results in death of host cell
Virulent virus (phage reproduction only by the lytic cycle)

5. Viral reproduction: Lysogenic Cycle
Genome replicated w/o destroying the host cell
Genetic material of virus becomes incorporated into the host cell DNA (prophage DNA)
Temperate virus (phages capable of using the lytic and lysogenic cycles)
May give rise to lytic cycle

6.
RNA viruses
Retroviruses: transcribe DNA from an RNA template (RNA--->DNA)
Reverse transcriptase (catalyzing enzyme)
HIV--->AIDS

7. http://highered. mcgraw-hill
Viroids and prions
Viroids: tiny, naked circular RNA that infect plants
Do not code for proteins, but use cellular enzymes to reproduce
stunt plant growth
Prions: “infectious proteins”
trigger chain reaction conversions
a transmissible protein
Ex.“mad cow disease”

8. Bacterial genetics
Nucleoid: region in bacterium densely packed with DNA (no membrane)
Chromosomes are circular not linear
Plasmids: small circles of DNA
Reproduction: binary fission (asexual)

9. Bacterial DNA-transfer processes
Different strains of bacteria exchanging and recombining DNA can occur 3 ways:
Transformation
Transduction
Conjugation

10. Transformation:
Genotype alteration by the uptake of naked, foreign DNA from the environment (Griffith expt.)

11. Transduction:
Transfer of host DNA from one cell to another by a virus.
generalized~ random transfer of host cell chromosome
specialized~ incorporation of prophage DNA into host chromosome

12. Conjugation: Direct transfer of genetic material
Pili / Conjugation tube create cytoplasmic bridges allows for the transfer of DNA from one bacteria to another
Sexual

13. Bacterial Plasmids
Small, circular, self-replicating DNA separate from the bacterial chromosome
Can enter and leave main genome at specific places
An episome is a plasmid incorporated in the bacterial chromosome.

14. Types of Bacterial Plasmids
F (fertility) Plasmid: codes for the production of sex pili (F+ or F-)
Strains with F plasmids are referred to as Hfr (high frequency of recombination)
R (resistance) Plasmid: codes for antibiotic drug resistance
No bueno (staph)

15. Transposons:
Segments of DNA that can move around to different positions in the genome of a single cell.
They can cause mutations and change the amount of DNA in the genome.
“jumping genes”
Barbara McClintock 1940s

16. The Operon Model Proposed by Francois Jacob and Jacques Monod
The Operon Model
Proposed by Francois Jacob and Jacques Monod
Unit of genetic function consisting of coordinately related clusters of genes with related functions (transcription unit)
Consists of:
Operator- controls access of RNA polymerase to genes
Promoter- RNA polymerase binding site begins transcription
Regulator- genes code for a repressor protein that binds to the operator
Structural genes - codes for the m-RNA and the protein product

17. Types of Gene Regulation:
Constitutive- genes are constantly transcribed
Repressible- operator is blocked inhibiting transcription “turned off”
Inducible- normally not transcribed but can be “turned on” in the presence of a specific molecule

18. Repressible (trp operon):
trp operon is transcribed readily in the absence of tryptophan
tryptophan present ~ acts as a corepressor
transcription is repressed when tryptophan binds to a regulatory protein

19. Inducible (lac operon):
No lactose : operon off
no transcription for lactose enzymes
lactose present: operon on
repressor protein is removed, transcription occurs.
transcription is stimulated when inducer binds to a regulatory protein

20. Lactose isn’t always enough
Even with lactose, the lac promoter doesn’t readily bind RNA polymerase
CRP (catabolite regulator protein) an accessory protein that stimulates RNA polymerase interaction.
Only binds when no glucose is in the cell
Low glucose inc. cyclic AMP (cAMP) levels
cAMP binds to CRP then it binds to the lac promoter
Lac operon is only transcribed when lactose is present and low glucose