Popular in Basic and Practical Microbiology
Popular in Microbiology
This 4 page Class Notes was uploaded by an elite notetaker on Tuesday October 13, 2015. The Class Notes belongs to 4000 at Ohio State University taught by Madhura Pradhan in Fall 2015. Since its upload, it has received 24 views. For similar materials see Basic and Practical Microbiology in Microbiology at Ohio State University.
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Date Created: 10/13/15
Chapter 8 Notes Key terms Genotype sequence of nucleotides in the DNA of an organism Phenotype Wildtype organism that has the typical characteristics of the species isolated from nature Auxotroph mutant that requires a growth factor Prototroph mutant that does not require a growth factor Point mutation mutation in which only one base pair is changed and DOES NOT change the reading frame Silent mutation codes for the wildtype amino Missense mutation mutation that changes the amino acid encoded by DNA Nonsense mutation mutation that generates a stop codon resulting in a shortened protein Null or knockout mutation totally inactivates the gene Transposon DNA segments that are mutagens which insert themselves into genes to inactivate them Spontaneous mutation random genetic changes that occur as a result of natural cellular processes Induced mutation caused by a factor outside of the cell Coniugation direct DNA transfer between bacterial cells DNAmediated transformation uptake of naked DNA by a competent recipient cell Horizontal gene transfer includes transformation transduction and conjugation Transduction the transfer of DNA via bacteriophages l Mobile Gene Pool variation in genes among strains of a species core genome found in all strains ex 75 of E coli genes found in all strains Genomic island large segment of a cell39s genome that originated in other species Plasmids typicaly do not encode genes essential to the life of the cell often the location of antibiotic resistance genes in bacteria Chromosomes ces cannot survive their loss found in all eukaryotes and prokaryotes Both plasmids and chromosomes made of doublestranded DNA contain an origin of replication ll Mutation A Mutations base substitution mutations an incorrect nucleotide is incorporated in place of another during DNA synthesis 2 major types 1 incorrect nucleotide is incorporated during DNA synthesis a Point mutation single base pair change 3 outcomes i Silent mutation codes for the same amino acid ii Missense mutation codes for a different amino acid iii Nonsense mutation codes for STOP 2 effect depends on the number of nucleotides a i Frameshift mutation 1 or 2 nucleotide pairs different codons translated and protein often nonfunctional ii 3 pairs one codon total 1 amino acid less impact depends on residue b Transposons addition mutation way in which antibiotic resistance genes move transposase enzymes move the DNA to a new location inactivates the gene in which it inserts cannot replicate independently occur during normal cell processes randomly and can be bene cial or harmful Mutation rate between 10394 and 103912 Reversion reversal of mutation Selective pressure environment makes it so that only some cells are able to survive and reproduce ex Antibiotics selecting for resistant bacteria caused by factor from outside of the cell ie radiation or chemicals a Chemical mutagens chemicals can modify or resemble DNA bases resulting in base pairing mistakes more common in AEROBIC environments ex ROS that damage DNA i Alkylating agents add allql group to G so now it pairs with T ii Nitrous acid converts cytosine to uracil so C now pairs with A instead of G iii Base analogs resemble nucleobases but Hbond different iv lntercalating agents insert between adjacent base pairs in the DNA strand to throw off spacing causing possible frameshift mutations b Radiation i Ultraviolet UV radiation mutates by thymine dimer formation that distorts the DNA helix and stops replication and transcription ii Xrays mutates by causing single and double strand breaks in DNA and also possibly altering nucleobases lll DNA Repair Mechanisms A Mismatch repair protein recognizes the mismatch and removes and replaces a short stretch of nucleotides B Glycolyase removes an oxidized nucleobase and is recognized and repaired C Photoreactivation ight is used to repair thymine dimers in prokaryotes D Excision repair enzymes recognize and repair major distortions in DNA E SOS repair deals with last chance repair of extensively damaged DNA rapidly increases rate of mutation so they rapidly evolve instead of dying IV Horizontal Gene Transfer A Conjugation o the way in which both Gram and cells can transfer DNA 0 requires contact between the donor and recipient cells 0 2 types plasmid and chromosome transfer F donor cells are high frequency recombinant Hfr cells when the is integrated into the chromosome a plasmid transfer coniuoative plasmids direct their own transfer ie F plasmid of E coli encodes proteins that promote transfer 4 steps of plasmid transfer 1 donor Fpilus makes contact with the cell wall of the recipient 2 Fpilus retracts to pull the donor and recipient together plasmidencoded enzyme cuts one strand at its origin of transfer 3 passing through the F pilus a singlestrand of the F plasmid enters the F cell acting as a complementary strand in order to generate an F plasmid 4 both the donor and recipient are now F now capable of donating F plasmid b chromosome transfer less common of the two types of transfer 1 Hfr cell produces F pilus 2 Single strand of chromosome is transferred to the recipient cell 3 DNA transfer is interrupted by the cells separated and chromosome breaking 4 Homologous recombination allows DNA to be integrated into the recipient cell but it stays F because it is incomplete B DNAMediated Transformation mechanism of gene transfer that involves the uptake of naked DNA by competent bacterial recipient cells capable of uptake of DNA competent cells have the ability to take up DNA from the environment highly regulated process 1 Doublestranded DNA molecule binds to surface receptor 2 Nucleases degrade one strand of doublestranded DNA at the cell surface 3 Singlestranded DNA enters cell after one strand has been degraded 4 Singlestranded DNA integrates into genome after entering the cell Grif th39s Experiment of Streptococcus pneumoniae C Transduction two types Specialized transfers only a few speci c genes due to excision mistakes during induction of temperate phage ony bacterial genes adjacent to integrated phage DNA are transferred in this case Generalized transfers any genes of the donor cell due to a quotpackaging errorquot during phage assembly in which host DNA fragments are incorrectly put into some phage heads uses a transducing particle phage coat with bacterial DNA to transfer bacterial cells donor DNA integrates into the recipient chromosome by homologous recombination
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