Ch. 16

• point mutations


  effect only one base pair and result in the addition or deletion of one nucleotide pair
• spontaneous mutations


  arise in all cells randomly and in the absence of any agent; occur from errors in replication, lesions, or actions of mobile genetic elements
• induced mutations


  result of exposure to a mutagen (physical or chemical agent)
• transition mutations


  purine for purine or pyrimidine for pyrimidine substitutions from nitrogenous base shifts (isomers)
• transversion mutations


  purine for pyrimidine or pyrimidine for purine; rarer than transition mutations
• base analogues


  a type of mutagen that is structurally similar to normal nitrogen bases but has different pairing properties; ex. pairs with guanine rather than adenine
• DNA-modifying agents


  a type of mutagen that changes the bases' structure and alters its base-pair specificity; ex. methyl-nitrosoguanidine and hydroxylamine
• intercalating agents


  a type of mutagen that distorts DNA to induce single nucleotide pair insertions and deletions
• wild type


  the more prevalent form a gene and its associated phenotype
• reversion mutation


  when the second mutation to reverse a forward mutation from wild type to mutant occurs at the original mutation site
• suppressor mutation


  when the second mutation to reverse a forward mutation from wild type to mutant occurs at a different site than the original mutation
• silent mutations


  change the nucleotide sequence of a codon but not the amino acid encoded by that codon; possible due to degeneracy (more than one codon for one amino acid)
• missense mutations


  a single base substitution that changes a codon for one amino acid into a codon for another; can be neutral if they have no effect on protein function
• nonsense mutations


  convert a sense codon (amino acid codon) to a nonsense codon (e.g. stop codon)
• frameshift mutations


  the insertion or deletion of base pairs within the coding region of the gene that causes the reading frame to be shifted
• conditional mutations


  mutations expressed only under certain environmental conditions; ex. fine in cold temps but dies in hot temps
• replica plating


  a mutant detection technique where a piece of velvet is used to pick up a colony and is stamped on a normal plate and a selective plate to isolate the mutant colony
• ames test


  tests if a substance is a mutagen by plating salmonella histidine auxotrophs with and without a test mutagen to see if revertants grow more with the test mutagen
• proofreading


  ability of the DNA polymerase to correct errors in nucleotide placement
• mismatch repair


  when proofreading fails, enzymes and polymerase cut out the mismatched pair from the unmethylated (new) strand and replace it
• excision repair


  corrects damage that causes distortion in the double helix shape; can be base repair or nucleotide repair but done in the same way
• recombinational repair


  recA cuts a template piece of DNA and replaces or fills areas where both bases of a pair are missing or damaged
• recombination


  the process in which one or more nucleic acid molecules are rearranged or combined to produce a new genotype; can be homologous (long strands) or site-specific
• vertical gene transfer


  transfer of genes from parents to offspring; crossing over and fusion of gametes in sexual reproduction
• horizontal gene transfer


  transformation, conjugation, or transduction occurs, and a donor DNA is put in a recipient cell; the donor DNA can then be integrated into the recipients genome or self-replicate (plasmid)
• transposition


  the movement of a mobile genetic element; e.g. insertion sequences, transposons, and ICE's (conjugation elements)
• simple transposition (cut and paste)


  transposase excises the transposable element, cleaves and inserts it into the target site
• replicative transposition


  a copy of the original transposable element is inserted into the target site
• F factor


  a conjugative plasmid (episome) in E. coli that directs the formation of sex pili and plasmid transfer from donor (F+) to recipient (F-)
• Hfr conjugation


  the donor (F+) transfers chromosomal genes but does not change the recipient into an F+ cell
• F' conjugation


  a F factor that has an accidental excised section of the bacterial chromosome in it (F' plasmid) mates with recipient
• mechanisms of drug resistance 


  modify the target of the antibiotic by mutation, drug inactivation, efflux pumps, and use of an alternate pathway
• R plasmids


  resistance genes in plasmids that code for enzymes that destroy or modify drugs