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48 Cards in this Set
- Front
- Back
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Vertical gene transfer |
parent to progeny -mutations: stable, heritable changes in seq of bases in DNA -euk-sexual reproduction and genetic recombination
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horizontal gene transfer |
-transfer of genes from ones independent, mature organism to the other -in bacteria, progeny are clones unless mutation
-conjugation -transformation -transduction |
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point mutations |
-most common -alteration of single no -addition or deletion of np
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less common mutations |
-larger -insertions, deletions, inversions, duplication and translocations of nucleotide sequences |
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spontaneous mutations |
-arise without exposure to external agents -may result from: errors in DNA replication spontaneously occuring lesions in DNA mobile genetic elements such as transposons |
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transition mutation |
pur to pur pyr to pry |
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transversion mutation |
pur to pyr pyr to pur |
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insertion or deletion |
of nucleotides -generally occur when there is a stretch of repeated nucleotides |
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DNA lesions |
-purine nucleotides can be depurinated, forming an apurinic site (loses its base) -pyrimidines can form an apyrimidinic site -cause polymerase to insert an incorrect nucleotide -adds random base |
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induced mutations |
-caused by agents that directly damage DNA
-base analogs structurally similar to normal bases mistakes occur when they are incorporated into growing chain
-DNA modifying agents alter a base's structure causing it to mispair
-intercalating agents distort DNA to induce single nucleotide pair insertions and deletions |
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UV radition |
causes thymine dimers |
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forward mutation |
wild type to mutant form |
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reversion mutation |
mutant form to wild type
-suppressor mutation occurs when the second mutation is at a different site than the original mutation |
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silent mutation |
no change in amino acid seq (wobble) |
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missense mutation |
pt mutation, change in a.a. seq |
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nonsense mutation |
change in a.a. to stop codon |
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frameshift mutation |
insertions or deletions -entire codon seq is changed downstream from mutation |
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morphological or lethal mutations |
can be |
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conditional mutations |
expressed at certain environments (ex. temp) |
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auxotrophic mutation |
-unable to make an essential macromolecule such as an amino acid or nucleotide -has conditional phenotype -auxotroph is mutant strain |
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phototroph |
wild type strain |
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resistance mutant |
resistance to pathogen, antibiotic, or chemical |
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mutations in regulatory sequences |
-operator or promoter seq. mutated
conditional lac operon mutants -mutation in operator site so repressor cant bind -operon is always transcribed and beta galactosidase is always synthesized because its on and repressor cant bind |
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mutations in tRNA and rRNA genes |
prot synthesis is disrupted |
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horizontal gene transfer |
-main mechanism by which bacteria and archaea evolve -increases virulence -occurs in 3 mechanisms (conjugation, transformation, transduction) -genes can be transferred to the same or different species |
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virulence |
-resistance genes -immuno sup. genes -immuno invasive -entry -lysis |
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merozygote |
recipient cell that is temp. diploid as result of transfer process in HGT (partial fertilized egg) |
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different HGT |
donor DNA uses conjugation, transformation or transduction to have it enter recipient cell
1. donor DNA can integrate into host DNA 2. donor DNA can form its own plasmid 3. donor DNA cant self-replicate and gets lost 4. donor DNA is restricted by host (nucleases break up DNA) |
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homologous recombination |
-most common -occurs where there are long stretches of similar nucleotide seq in 2 DNA molecules -double strand break occurs between molecules, allowing exchange (crossing over) -Rec (recombination) prots carry out the process -RecA most important |
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site-specific recombination |
-small region inserted -occurs at specific target sites in DNA -mediated by recombinaze enzymes (NOT rec prot) -used by: viruses to integrate into host DNA transposable elements to move from one place to the other
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site specific recombinace prots |
-integrase -revolvase -transposase |
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transposable elements |
-specific DNA segments that can repeatedly insert into 1 or more sites or into one or more genomes by transposition -"jumping genes" -makes 2 copies in case one gets mutated |
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IS elements |
-insertion sequences -most simple transposable element -short -inverted repeats -each IS has its own characterisitic IR seq
DR(direct rep) IR(inverse rep) transposase gene IR DR
IR trans IR is insertion sequence |
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composite transposon |
-flanked on both sides by IS elements *see photo |
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unit transposon |
not associated with IS *see photo |
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integrative conjugative elements |
-ICEs -contains genes for conjugative transfer (ex. resistance gene) |
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simple transposition |
-cut and paste transposition -transposase cuts out, cleavage of new target site and ligation into site |
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repair enzymes |
fill in gaps with direct repeats |
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replicative transposition |
2 genes coding for enzymes -transposase- cleaves both ends of transposon and moves it -donor doesnt change
-resolvase- cleaving to originial so you have 2 double stranded copies
-original transposon remains at parental site in DNA
-copy is inserted into target DNA |
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bacterial conjugation |
-transfer of DNA by direct cell to cell contact -depends on conjugative plasmid (transfer copies of themselves to other bacteria during conjugation) -direct cell to cell contact mediated by the sex pilus -unidirectional DNA transfer from donor to recipient |
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F factor |
plasmid is the best studied conjugative plasmid is an episome -can integrate into host chromosome or exist independently |
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F plasmid integration |
-F factors have insertion sequences (IS) -assists in plasmid integration |
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F Factor Mediated Conjugation-1 |
-donor cells contain the F plasmid are F+ -F- cells are recipients of the plasmid -F factors contain the info for formation of sex pilus (type IV secretion system) attach F+ cell to F- cell for DNA transfer during bacterial conjugation |
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F Factor Mediated Conjugation-2 |
-rolling circle replication is initiaited by the relaxosome prot complex -As F factor is replicated, the displace strand and attached relaxase enzyme move through type IV sex system into recipient cell -coupling factor binds relaxase bringing it to the sec system |
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F Factor Mediated Conjugation-3 |
-strand that is transferred called T DNA -Relaxase joins 2 ends together to make DNA circular again -F- cell becomes F+ -chromosomal genes usually not transferred |
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rolling circle replication |
*see photo and video |
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HFr Conjugation |
-donor HFr cell has F factor integrated into its chromosome -donor genes are transferred to recipient cell -a complete copy of the F factor is usually not transferred -gene transfer can be clockwise or counterclockwise |
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F' conjugation |
-result when F factor incorrectly leaves the host chromosome -some host genes have been removed along with some of the F factor -these genes can be transferred to a second host cell by conjugation |
