Genetics 4

terminator

DNA sequence that signals the RNA polymerase to cease transcription

frameshift suppressor

a +1 base pair insertion in the anticodon portion of a tRNA gene, resulting in a mutant tRNA that can read a 4-base codon during translation

nonsense codon

a 3-base sequence that directs ribosomes and tRNA to cease translation and release the polypeptide

initiation codon

a 3-base sequence that directs ribosomes and tRNA to insert the first residue of a nascent polypeptide

promoter

a DNA base pair sequence that specifies transcription start points for RNA polymerase

nonsense suppressor

a base pair substitution in the anticodon portion of a tRNA gene, resulting in a mutant tRNA that can read one or more types of stop codons in mRNA and insert an amino acid into the nascent protein product

missense suppressor

a base pair substitution in the anticodon portion of a tRNA gene, resulting in a mutant tRNA that misreads a particular codon during translation

missense mutation

a base pair substitution mutation in a gene that causes incorporation of an incorrect amino acid at one residue of the protein product

nonsense mutation

a base pair substitution mutation in a gene that creates a stop codon in the mRNA, leading to premature termination of translation and a truncated protein product

complementation test

a method for determining the functional relationship between two mutations, i.e., whether they are defective in the same gene or different genes

alkylating agent

a mutagen that alkylates DNA bases to cause base substitutions (both transitions and transversions); examples include ethyl methane sulfonate (EMS) and nitrosoguanidine (NTG)

base analog

a mutagen that mimics a DNA base, but with error-prone Watson-Crick pairing, leading to base substitution mutations; these mutagens specifically cause transition mutations; examples include 2- aminopurine (2-AP; an adenine analog) and 5-bromouracil (5-BU; a thymidine analog)

revertant

a mutant that has regained function through an unspecified mutational event

frameshift mutation

a mutation that inserts or removes 3n ± 1 base pairs in the coding region of a gene, shifting translation to an incorrect frame of reference, which nearly always results in a nonfunctional protein product

intron

a noncoding portion of a gene that must be removed by mRNA splicing before translation

suppressor

a second-site mutation that alleviates the defective phenotype caused by another mutation; depending on the nature of the original mutation, these compensatory mutations can occur in the same codon (intracodon), same gene (intragenic), or another gene (intergenic)

anticodon

a three-base sequence in tRNA that base pairs with a complementary codon in mRNA to add an amino acid to the nascent polypeptide during translation antisense strand the template DNA strand that directs mRNA synthesis

degeneracy

an attribute of the genetic code in which multiple codons can specify the same amino acid

RNA polymerase

an enzyme that synthesizes RNA molecules from DNA templates

reversion

an unspecified mutational event that restores function to a mutant

cistron

another name for a gene; derived from the cis-trans test used for complementation analysis codon a three-base sequence in mRNA that specifies an amino acid during translation by base pairing with the anticodon of a charged (amino acid-bearing) tRNA

post-translational

events that happen subsequent to translation (e.g., disulfide bond formation, covalent modification, proteolytic processing) that influence the stability or functional activity of a protein

post-transcriptional

events that happen to gene transcripts subsequent to transcription (e.g., splicing, addition of a leader or tail) that influence the stability or functional activity of an mRNA molecule

mutagenesis

experimental induction of mutations via treatment of DNA with radiation, chemicals, etc.

transcription

generation of an mRNA transcript of a gene's protein-coding information; the first step in the central dogma readout of DNA information into protein sequence

intercalating agents

mutagens that cause ±1 bp frameshift mutations by inserting between bases in a replicating DNA molecule; proflavin, acridines, and ICR compounds are commonly used examples of these mutagens

spontaneous mutations

mutational changes in DNA sequences that arise without explicit mutagenic treatments

mRNA leader, mRNA tail

noncoding sequences at the 5' or 3' end of an mRNA molecule that regulate its functionality and half-life

translation

production of a polypeptide using a gene's coding information in mRNA; the second step in the central dogma readout of DNA information into protein sequence

mutational hotspots

regions of a gene in which mutational changes are found at high frequency relative to other segments of the gene; these can reflect either functionally critical segments of the protein product or highly mutation-prone portions of the DNA sequence

wobble pairing

relaxed codon-anticodon base pairing in the third-bas

bypass suppression

restoration of a more normal phenotype in a mutant via a suppressor that activates or creates an alternative pathway or function; the original mutant gene product does not regain function

pseudoreversion

restoration of partial or full function to a mutant gene through a mutational event that does not restore the wild-type gene sequence

isoaccepting tRNA's

tRNA species with different anticodons that insert the same amino acid during translation

sense strand

the coding DNA strand whose base sequence corresponds to that of the mRNA

exons

the coding portions of genes that contain introns

mutational site

the locus of a DNA lesion that causes a mutant phenotype; defined by recombination tests between mutant DNA molecules

colinearity

the nature of the structural and functional relationship between the coding information of a gene and the amino acid sequence of its protein product

reading frames

the triplet groups of bases in DNA or mRNA that might be read by the translation machinery