bi323 chapter 16

mutation

stable, heritable change in nucleotide sequence, may or may not affect phenotype

spontaneous

mistake during replication, translation, develop in absence of any added agent, thought to arise randomly

induced

exposure to mutagen

tautomeric shifts

abnormal pairings of nucleotides, a spontaneous mutation

frameshift

deletion or addition of base pairs that alters reading frame

base analogs, DNA modifying agents, intercalating agents, DNA damaging agents

what are examples of agents that can induce mutations

forward mutation

going from wild type to mutant form

reversion mutations

a second mutation occurs at the same site and leads back to the wild type phenotype, mutant phenotype to wild type

suppressor mutation

occurs at a second site and not the original mutation site, a reversion mutation

silent mutations

least severe, does not lead to a different amin acid, would not know looking at the protein there is a mutation

missense mutation

change of nucleotide leads to a different amino acid, one base pair substition

nonsense mutation

early termination of the sequence

conditional mutations

expressed only under certain conditions

biochemical mutations

changes in metabolic capabilities

auxotroph

biosynthetic pathway mutants, cannot synthesize product of pathway required for growth

prototrophs

grow in minimal media without supplements

resistance mutations

resistance to pathogen, chemical, or antibiotic

regulatory mutations

changes in regulatory sequences, alter control of gene expression

replica plating technique

how auxotroph mutants are detected

recombination

rearranging and combining of more than 1 nucleic acid molecules to produce a new nucleotide sequence, generates new combination of genes

horizontal gene transfer

transfer of DNA from donor organism to recipient, via conjugation, transformation, transduction

exogenote

external donor

endogenote

the original genome before the donor piece is received

merozygote

partially diploid, contains both endogenote and exogenote

conjugation

horizontal gene transfer through direct cell to cell contact

transformation

foreign genetic material is taken up from the environment

transduction

when viruses transfer DNA from a donor to a recipient

double-strand break model

homologous recombination, results from DNA strand breakage and reunion, catalyzed by rec proteins

nonreciprocal

homologous recombination, incorporation of DNA single strand into chromosome, forms heteroduplex DNA

site specific recombination

insertion of primarily nonhomologous DNA into chromosome, only short region of homology, often during viral genome integration

transposition

segments of DNA that moves in the genome, sometimes called “jumping genes” or transposons

transposable elements

widespread mobile DNA segments, carry required genes, do not require large homology regions, no life cycle, can not replicate autonomously

insertion sequences

simplest, 750-1600 bp, possess only genes encoding enzymes required for transposition, bounded by inverted repeat

composite transposons

carry genes in addition to those needed for transposition, central region flanked by IS elements, anitbiotic resistance

simple

transposition method where transposase recognizes the ends of the TE, cuts them, cleaves the new target site and ligates, the insertion generates direct repeats of flanking host DNA, “cut and paste”

replicative

transposition method where transposase makes the cuts, strands are exchanged, resolvase catalyzes the recombination of the 2 elements, original transposon remains at parental site and a copy is inserted in the target site

mutation in coding region, arrest of translocation or transcription, activation of genes, generation of new plasmids

what are the effects of transposition

plasmid

small, circular dsDNA molecules

episomes

can exist with or without integrating

conjugative plasmids

transfer copies via conjugation, genes encoding pili

fertility factors

conjugative plasmids, major role in conjugation, formation of sex pili, integrative, many also episomes

resistance factors

plasmids with antibiotic resistance genes, destroy and modify antibiotics, usually not integrative, spread of resistance in population and among species

Col plasmids

encode colicin a type of bacteriocin, proteins that destroy closely-related bacteria, kills E.coli, some conjugative some carry resistance genes

virulence plasmids

carry virulence genes

metabolic plasmids

carry genes for metabolic processes, nitrogen fixation

Joshua Lederberg and Edward Tatum

discovered conjugation

Bernard Davis

U-tube experiment, discovered contact was required for conjugation

Fred Griffin

discovered transformation

competent cell

capable of taking up DNA

chemical transformation

calcium chloride treatment, heat and DNA, recovery and platin

electroporation

make protoplasts, cells and DNA into cuvette, apply current, recovery and plating

virulent bacteriophages

reproduce using lytic life cycle (destroy host cell)

temperate bacteriophages

reproduce using lysogenic life cycle

generalized transduction

any part of bacterial genome can be transferred, during lytic cycle, during viral assembly, fragments of host DNA mistakenly packed into phage head

specialized transduction

by temperate phages, only specific portion of bacterial genome is transferred, occurs when prophage is incorrectly excised, error in lysogenic cycle