Card Set Information
Infect or kill immediately
Can enter and lay dormant and can go into the lytic cycle
Gag and pol construct viral structure
Arbor viruse need?
A go between.. insects � west Nile
Bacteria � asexual reproduction
Parasexual - sexual relationships with another organism � one is sharing information - no go between
Prototrophs � have everything they need to carry out processes if optimal conditions
Transformation � uptake of free DNA
Calcium chloride method � breaks down cell membrane from plasmids to enter � cold
Electroporation � hook up to give electric shock and ipens channels in cell wall and DNA go in
Direct transfer from a bacteria to a host
Transfer of bacterial DNA by bacteriophages
LPS lipopolysaccharides � immune response � shuts this off
Cells are capable of taking up DNA and using it
High frequency recombination � recombine with main chromosomes
Cre-Recombinase � rely on a food additive to induce recombination and insert or eject pieces of DNA - can turn on and off different things
Episomes � genetic element
Transformation � is cell contact required? Sensitive to DNase?
Conjugation � is cell contact required? Sensitive to DNase?
Transduction � is cell contact required? Sensitive to DNase?
Bacteria and Viruses
� Small size
� Rapid reproduction
� Selective media (e.g., antibiotics)
� Simple structures and physiology
� Genetic variability
� Complete genome sequences
Their small size, short generation time, and simple structures have made
bacteria and viruses valuable model systems for genetic studies.
Many basic concepts of genetics were first deduced from studies of
bacteria and viruses.
The Genetics of Viruses
Viruses can only reproduce by infecting living host cells.
Bacteriophages are viruses that
Several important genetic concepts have been discovered through studies of bacteriophages.
� Double-stranded DNA genome
� Protein head
� Genome contains 168,800 base pairs and 150 characterized genes
� Lytic phage
� Double-stranded DNA genome
� Genome contains, 48,502 base pairs and about 50 genes
� May be lytic or lysogenic
Mapping Genes in Bacteriophage
� Genes may be mapped based on recombination frequencies.
� Host bacteria are infected with two types of phage; progeny phage are screened for recombination.
� Map distances are calculated as the average number of crossovers between genetic markers.
� Temperature-sensitive (ts) mutations
� Plaque morphology (rapid lysis; lysis inhibition)
� Host range
Map of Bacteriophage T4
� Linear chromosome
� Circular map
: The T4 chromosome is terminally redundant and circularly permutated.
Viruses are obligate parasites that can reproduce only by
infecting living host cells.
Bacteriophages are viruses that
Bacteriophage T4 is a lytic phage that infects E. coli, reproduces, and lyses the host cell.
Bacteriophage lambda can enter a lytic pathway, like T4, or it can enter a lysogenic pathway, during which its chromosome is inserted into the chromosome of the bacterium.
In its integrated state, the lambda chromosome is called a
prophage, and it�s lytic genes are kept turned off.
Bacteria contain genes that mutate to produce altered phenotypes. Gene transfer in bacteria is unidirectional�
from donor cells to recipient cells.
� One main chromosome with a few thousand genes.
� Variable number of plasmids and episomes.
� Asexual reproduction by simple fission.
� Parasexual processes occur.
Phenotypes in Bacteria
� Colony color and morphology
� Nutritional mutants for energy sources
� Prototrophs and auxotrophs
� Dur and antibiotic resistance
Bacteria usually contain one main
Wild-type bacteria are prototrophs;
they can synthesize everything they need to grow and reproduce given an energy source and some inorganic molecules.
Auxotrophic mutant bacteria require
additional metabolites for growth.
Gene transfer in bacteria is unidirectional;
genes from a donor cell are transferred to a recipient cell, with no transfer from recipient to donor.
Mechanisms of Genetic Exchange in Bacteria
Bacteria exchange genetic material through three different parasexual processes.
a bacteriophage transfers DNA from a donor cell to a recipient cell.
In generalized transduction,
a random fragment of bacterial DNA is packaged in the phage head in place of the phage DNA.
In specialized transduction,
recombination between the phage chromosome and the host chromosome produces a phage chromosome containing a piece of bacterial DNA.
A plasmid is a
genetic element that can replicate independently of the main chromosome in an extrachromosomal state.
Most plasmids are not required for the
survival of the host cell.
Plasmids in E. coli
�F Factor (Fertility Factor)
�R Plasmids (Resistance Plasmids)
�Col Plasmids (synthesize compounds that kill sensitive cells)
An episome is a genetic element that is not essential to the host and that can either replicate autonomously or be integrated into the bacterial chromosome.
Integration depends on the presence of IS elements.
Three parasexual processes occur in bacteria.
�transformation, conjugation, and transduction�
These processes can be distinguished by two criteria:
whether the gene transfer is inhibited by deoxyribonuclease and whether it requires cell contact.
Transformation involves the uptake of
free DNA by bacteria.
Conjugation occurs when a
donor cell makes contact with a recipient cell and then transfers DNA to the recipient cell.
Transduction occurs when a
virus carries bacterial genes from a donor cell to a recipient cell.
self-replicating extrachromosomal genetic elements.
Episomes can replicate
autonomously or as integrated components of bacterial chromosomes.
F factors that contain chromosomal genes (F� factors) are trasnferred to F-cells by
Closely linked genes can be mapped in bacteria by
Genetic Exchange in Bacteria
� Mutation is the source of new genetic variation.
� Recombination produces new combinations of allele.
� Transformation, conjugation, and transduction generate new combinations of genes in bacteria to allow bacteria to adapt to new environments.
Parasexual recombination mechanisms produce
new combinations of genes in bacteria.
Parasexual mechanisms enhance the ability of
bacteria to adapt to changes in the environment.