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

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

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 http://darwin.bio.uci.edu/~faculty/wagner/hsvbinding.html

Viral reproduction: Lytic Cycle http://www.dnatube.com/view_video2.php?viewkey=247bc31d0eb4e7aeb07a Viral reproduction: Lytic Cycle Immediately takes over the host cell and begins making new viruses. The lytic cycle: 1- attachment 2- injection 3- hydrolyzation 4- assembly 5- release Results in death of host cell Virulent virus (phage reproduction only by the lytic cycle) http://pgl.ufl.edu/modules/mysterious_invaders/lytic.htm

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 http://pgl.ufl.edu/modules/mysterious_invaders/lytic.htm

http://www.metacafe.com/watch/374305/queen_we_will_rock_you_feat_by_dj77/ RNA viruses http://cyrusxface.imeem.com/music/yPIUbLWy/styx_come_sail_away/ Retroviruses: transcribe DNA from an RNA template (RNA--->DNA) Reverse transcriptase (catalyzing enzyme) HIV--->AIDS http://www.metacafe.com/watch/354325/hiv_biology_i/

http://highered. mcgraw-hill http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter26/animations.html# Viroids and prions http://www.dnatube.com/view_video2.php?viewkey=2435a724a8f30fddadd9 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” http://learn.genetics.utah.edu/features/prions/

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) http://www.microbelibrary.org/microbelibrary/files/ccImages/Articleimages/MondoMedia/2bhirez.mov

Bacterial DNA-transfer processes Different strains of bacteria exchanging and recombining DNA can occur 3 ways: Transformation Transduction Conjugation http://www.metacafe.com/watch/427388/the_joys_of_eating_out/

Transformation: Genotype alteration by the uptake of naked, foreign DNA from the environment (Griffith expt.) http://www.dnatube.com/view_video2.php?viewkey=42911677c739ee173448

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 http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_2.html

Conjugation: Direct transfer of genetic material Pili / Conjugation tube create cytoplasmic bridges allows for the transfer of DNA from one bacteria to another Sexual http://www.dnatube.com/view_video2.php?viewkey=4c64c85ca5b5690ee529

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.

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)

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 http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_5.html

The Operon Model Proposed by Francois Jacob and Jacques Monod http://ejanime.imeem.com/music/w0ccTTGP/techno_crazy_techno_song/ 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

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 http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter12/animation_quiz_3.html

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 http://bcs.whfreeman.com/thelifewire/content/chp13/1302002.html

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 http://bcs.whfreeman.com/thelifewire/content/chp13/1302001.html

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 http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter12/animation_quiz_4.html