Ch. 8 Pt. 2: Microbial Gentics

constitutive genes

expressed at a fixed rate

inducible gene

a gene that turns on by responding to specific stimulus

repressible gene

gene that is active by default but can be turned off by specific molecule

co repressor

turns off repressible gene

promoter

segments of DNA where RNA polymerase initiates transcription

operator

segment of DNA that controls transcription of structural genes

operon

set of operator and promoter sites and the structural genes they control

inducible operon

set of operator and promoter sites and the structural genes they control

mutation

a permanent change in the base sequence of DNA

mutagen

agents that cause mutations

spontaneous mutation

occur in the absence of a mutagen

spontaneous mutation rate

1 in 10^9 base pair or 1 in 10^6 replicated gene

base substitution (point mutation)

change in one base in DNA

missense mutation

base substitution results in change in an amino acid

nonsense mutation

base substation results in a nonsense(stop) codon

frameshift mutation

insertion or deletion of one or more nucleotide pairs

positive selection

detects mutant cells because they grow or appear different than unmutated cells

negative selection

detects mutant cells that cannot grow or perform certain functions

auxotroph

mutant that has a nutritional requirement absent in the parent

genetic recombination

exchange of genes between two DNA molecules; creates genetic diversity

transformation

genes transferred from one bacterium to another as “naked” DNA

conjugation

plasmids transferred from one bacterium to another

F factor

donor cells that carry plasmid

dHfr cells

contain the F factor on the chromosome

bacteriophage

used to transfer DNA from a donor cell to a recipient

generalized transduction

random bacterial DNA is packaged inside a phage and transferred to a recipient cell

plasmids

self-replicating circular pieces of DNA often coding for proteins

conjugative plasmid

carries genes for sex pili and transfer of the plasmid

resistance factor (R factor)

encode antibiotic resistance

transposons

segments of DNA that can move from one treason of DNA to another

insertion sequence

code for transposase that cuts and reseals DNA

genetic diversity

caused by mutations and recombination

obligatory intracellular parasites

require living host cells to multiply, no DNA or RNA, protein coat, no ribosomes, no ATP-generating mechanism

bacteriophages

viruses that infect bacteria

bacteriophage length

from 20nm to 1000nm

viron

complete, fully developed viral particle

capsid

protein coat made of capsomeres

envelope

lipid, protein, and carbohydrate coating on some viruses

spikes

projections from outer surface

helical viruses

hollow, cylindrical capsid

polyhedral viruses

many sides

complex viruses

complicated structures

virus nomenclature

family, subfamily, genus, species

plaques

 clearing on a lawn of bacteria on the surface of agar

plaque forming units

measure the number of infection virus particles in a sample, determined by a plaque assay

viral growth for testing

done in living animals or embryonated eggs

cytopathic effect

virally infected cells are detected via their deterioration

methods of viral identification

 cytopathic effects, serological tests, nucleic acids

viral multiplication

invade host cell, eclipse period, virions released from host cell, acute infection

T-even bacteriophage

the Lytic Cycle: attachment, penetration, biosynthesis, maturation, release

attachment

phage attaches by the tail fibers to the host cell

penetration

phage lysozyme opens the cell wall; tail sheath contracts to force the tail core and DNA into the cell

biosynthesis

production of phage DNA and proteins

maturation

assembly of phage particles

release

phage lysozyme breaks the cell wall

lytic cycle

phage causes lysis and death of host cell

lysogenic cycle

 phage DNA incorporates into host cell DNA

prophage

inserted phage DNA

results of the lysogenic cycle

cells become immune to reinfection by the same phage

phage conversion

the host cell exhibits new properties

multiplication of animal viruses

attachment, entry by receptor-mediated endocytosis or fusion, uncoating by viral or host enzymes, biosynthesis, maturation, budding or rupture

biosynthesis of RNA viruses

virus multiplies in the host cell’s cytoplasm using RNA-dependent RNA polymerase

ssRNA(sense) strand

viral RNA serves as mRNA for protein synthesis

ssRNA(antisense) strand

 viral RNA is transcribed to a + strand to serve as mRNA for protein synthesis

dsRNA

 double stranded RNA

reverse transcriptase

used by single-stranded RNA to produce DNA rom the viral genome

provirus

 viral DNA that integrates into the host chromosome

retroviridae

HIV, oncoviruses, viral RNA is transcribed to DNA which can integrate into host DNA

cancer

can be caused by viruses

sarcoma

cancer of connective tissue

adenocarcinoma

cancers of glandular epithelial tissue

oncogenes

transform normal cells into cancerous cells

oncogenic viruses

 become integrated into the host cell’s DNA and induce tumors

tumor-specific transplant antigen

specific transplant antigen: a unique marker on cancer cells that is not found on normal cells and can trigger an immune response that attacks and destroys the tumor

persistent viral infecition

occurs gradually over a long period(measles)

infection rate of viruses

Virus enters, acute infection, persistent infection, latent infection