lec. 2

Comprehensive vocabulary flashcards detailing the types of genetic mutations, screening versus selection methods, conditional and resistant mutant phenotypes, and the positional impacts of mutations on gene function.

Loss of Function

A mutation that generally requires a screen to identify, as both wild-type and mutant cells survive under non-selective control conditions and colonies failing to grow on selective plates must be visually identified.

Gain of Function

A mutation that generally enables a selection strategy, where growth conditions only permit the survival and colony formation of cells carrying the mutation.

Auxotrophic Mutant

A mutant organism carrying a loss-of-function mutation in a metabolic pathway (such as tryptophan biosynthesis) that prevents it from synthesizing an essential compound, thereby requiring nutrient supplementation to grow.

Conditional Lethal Mutant

A mutant whose viability depends on environmental conditions, growing normally under permissive conditions but dying or failing to grow under non-permissive conditions; useful for studying essential genes by toggling protein function.

Temperature-Sensitive (ts) Mutant

The most common class of conditional lethal mutant, typically resulting from a modest amino acid substitution that allows the protein to remain stable and functional at permissive temperatures but causes instability and loss of function at elevated temperatures.

Permissive Temperature

A non-selective temperature (e.g., $37^\circ\text{C}$) at which a temperature-sensitive mutant protein remains stable and functional, permitting normal cell growth alongside the wild type.

Non-Permissive Temperature

A selective temperature (e.g., $42^\circ\text{C}$) at which a temperature-sensitive mutant protein becomes unstable and non-functional, preventing cell growth.

Resistant Mutant

A mutant that survives exposure to a toxic agent or antibiotic due to an altered target, such as bacterial gyrase mutants (gyrA) that replicate in the presence of ciprofloxacin.

Ciprofloxacin Selection

A selective technique in which ciprofloxacin inhibits wild-type DNA gyrase activity and halts replication in wild-type cells, allowing only resistant gyrA mutants to form visible colonies.

Point Mutation

A mutation caused by a single base pair change at the DNA level, which within a protein-coding sequence can result in a missense, nonsense, or same-sense alteration.

Missense Mutation

A base pair substitution within a protein-coding gene that changes a codon to specify a different amino acid; deleterious consequences depend on whether amino acid functional groups change or if the alteration occurs in a critical region, such as an enzyme active site.

Nonsense Mutation

A base pair substitution within a protein-coding gene that introduces a premature stop codon, exerting its most severe disruptive effect when located near the beginning or middle of the gene.

Same-Sense Mutation

A base pair change in a protein-coding sequence that alters the nucleotide sequence without changing the specified amino acid, typically exerting no functional effect on the resulting protein.

Frameshift Mutation

A mutation resulting from an insertion or deletion of a number of nucleotides not divisible by $3$ within a coding region, altering the triplet reading frame and causing all downstream translated sequences to become non-functional.

Wobble Position

The third nucleotide position of a codon where base substitutions frequently code for the same amino acid (for example, $AGG \rightarrow AGA$ or $AGG \rightarrow CGG$, both encoding Arg), creating degeneracy in the genetic code.

Regulatory Region Mutation

A mutation occurring outside of the translated coding sequence (position 1) that has no reading frame or sense designation, but alters expression levels by affecting a promoter, regulator binding site, or ribosome binding site (RBS).

Non-Coding Insertion

An insertion occurring outside of the open reading frame (such as upstream of the start codon) that affects regulatory DNA sequences but causes no shift in the reading frame or translated protein sequence.

Antibiotic Resistance Cassette

A defined DNA sequence conferring resistance to an antibiotic, commonly inserted into a genome to disrupt and knock out target gene function.