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