DNA Mutation and Repair

Comprehensive vocabulary flashcards covering the molecular nature, mechanisms, environmental causes, and repair pathways of DNA mutations.

Mutation

A stable, heritable change in DNA structure in which the base sequence is altered.

Point Mutation

A base substitution mutation in which one base in the DNA sequence is substituted for another.

Transition Mutation

A point mutation involving the substitution of a purine to another purine ($\text{A}$ to $\text{G}$) or a pyrimidine to another pyrimidine ($\text{C}$ to $\text{T}$).

Transversion Mutation

A point mutation in which a purine is replaced by a pyrimidine, or a pyrimidine is replaced by a purine.

Missense Mutation

A point mutation (also called a nonsynonymous mutation) that results in one altered codon specifying a different amino acid.

Conservative Missense Mutation

A missense mutation where the altered codon specifies a chemically similar amino acid.

Nonconservative Missense Mutation

A missense mutation where the altered codon specifies a chemically dissimilar amino acid.

Nonsense Mutation

A base substitution that generates a premature stop codon, terminating the polypeptide chain at that position.

Synonymous Mutation

A point mutation (also referred to as a sense mutation) in which the altered codon still specifies the same amino acid.

Frameshift Mutation

A genetic mutation caused by indels (insertions or deletions) of bases that shifts the reading frame during mRNA translation.

Replication Slippage

A replication error occurring at repetitive sequences where newly synthesized strand slippage causes base addition, or template strand slippage causes base deletion.

Regulatory-Region Mutation

A mutation occurring in non-coding regions containing crucial DNA binding sequences (such as RNA polymerase binding sites), resulting in unpredictable functional effects.

Tautomeric Shift

The reversible isomerization of nucleotide bases from their common keto/amino forms to rare enol/imino forms, changing their hydrogen-bonding properties and causing mispairing during replication.

Base Analogs

Chemical compounds that closely resemble natural nucleotide bases and can be erroneously incorporated into DNA during replication.

Spontaneous Deamination

The removal of an amine group from a base, converting cytosine to uracil, adenine to hypoxanthine, or guanine to xanthine.

Depurination

The spontaneous breakage of the glycosyl bond linking purine bases to deoxyribose, resulting in the loss of approximately $10^4$ purines per cell per day in mammalian cells.

AP Site

An apurinic or apyrimidinic site (also called an abasic site) created when a purine or pyrimidine base is lost from the sugar-phosphate backbone.

Oxygen Radical Damage

DNA damage mediated by reactive oxy radicals, such as $[\text{FeO}]^{2+}$, that results in the destruction and breakage of deoxyribose sugar rings.

Nitrous Acid ($\text{HNO}_2$)

A chemical mutagen produced when nitrites from preserved meats react with stomach acid, inducing oxidative deamination of bases.

Alkylating Agents

Chemical mutagens that transfer methyl or ethyl groups to DNA bases, modifying their base-pairing characteristics.

Intercalating Agents

Planar chemical molecules—such as ethidium bromide, acridine orange, and actinomycin D—that wedge between adjacent base pairs, distorting the double helix and causing frameshift indels.

UV-C Radiation

Ultraviolet light with a wavelength of $180-290\,\text{nm}$; the most energetic and germicidal fraction of UV, absorbed by the Earth's ozone layer.

UV-B Radiation

Ultraviolet light with a wavelength of $290-320\,\text{nm}$, constituting the major lethal and mutagenic fraction of sunlight.

UV-A Radiation

Ultraviolet light with a wavelength of $320\,\text{nm}$ to visible light ("near UV") that produces few pyrimidine dimers but causes damage primarily through oxygen radical generation.

Pyrimidine Dimer

A DNA lesion induced by UV radiation where adjacent pyrimidines (e.g., adjacent thymines) become covalently joined via a cyclobutyl ring, distorting the helix and blocking replication.