lec 13-Genetics and Molecular Biology: Gene Mutations Flashcards

Vocabulary-style flashcards covering gene mutations, their classifications, mechanisms of origin (spontaneous and induced), transposable elements, DNA repair pathways, and associated genetic diseases based on the 4BBY1070 lecture notes.

Mutation

A change in the DNA sequence.

Gene mutations

Changes in the nucleotide sequence within individual genes that can affect protein structure or gene expression.

Somatic mutations

Mutations occurring in any cell of the body except germ cells; these can lead to cancer and are NOT inherited by offspring.

Germ-line mutations

Mutations occurring in gametes that are inherited by offspring.

Silent mutation

A base-pair substitution that does NOT change the amino acid due to the redundancy of the genetic code.

Missense mutation

A base-pair change that results in an amino acid change in the protein.

Nonsense mutation

A base-pair change that creates a translation termination (stop) codon in place of an amino acid codon, resulting in a truncated polypeptide.

Conservative amino acid substitution

A missense mutation that substitutes a chemically similar amino acid, such as alanine ($-CH_3$) for glycine ($-H$), and is less likely to alter function.

Nonconservative amino acid substitution

A missense mutation that substitutes a chemically different amino acid, such as glycine ($-H$) for glutamate ($-CH_2-CH_2-COO^-$), which is more likely to alter protein function.

Frameshift mutation

The addition or deletion of one or more bases that changes the reading frame and alters all downstream amino acids.

Regulatory mutations

Point mutations that alter the amount of protein produced by affecting regions such as promoters and other protein binding sites without changing the amino acid sequence.

Induced mutation

A mutation produced by the action of a mutagen, an environmental agent that alters nucleotide sequence.

Spontaneous mutation

A mutation arising in the absence of a known mutagen, often caused by errors in DNA replication.

Proofreading

The $3'$ to $5'$ exonuclease function of DNA polymerase that corrects wrong nucleotide insertions $99$% of the time.

Trinucleotide repeat disorders

Disorders caused by DNA polymerase slipping during replication, increasing the number of repeats; an example is Huntington’s disease involving $36$ or more CAG repeats.

Tautomers

Alternative structures of DNA bases (amino vs. imino; keto vs. enol) with differences in bonding that can lead to base-pair mismatches.

DNA transposons

Transposable elements found in both prokaryotes and eukaryotes that move position using the protein transposase.

Retrotransposons

Transposable elements in eukaryotes that move via an RNA intermediate and require reverse transcriptase and integrase.

Base analogs

Chemicals similar to nitrogenous bases but with altered pairing properties, such as $5\text{-bromouracil}$ ($5\text{-BU}$) which replaces thymine.

Intercalating agents

Flat, planar molecules like proflavin or ethidium bromide that wedge between base pairs, distorting the helix and causing frameshift mutations.

Photoreactivation repair

A repair mechanism where the photoreactivation enzyme (PRE), such as photolyase in E. coli, cleaves thymine dimer bonds.

Base excision repair

A repair process involving base-specific DNA glycosylase, AP endonuclease, DNA polymerase, and DNA ligase to replace noncomplementary bases like uracil.

Nucleotide excision repair

A pathway that repairs DNA-distorting lesions like thymine dimers; in E. coli, this involves the uvrA, uvrB, and uvrC proteins excising $13$ nucleotides.

Xeroderma pigmentosum

A hereditary disease caused by mutant alleles of genes involved in nucleotide excision repair, leading to extreme photosensitivity and malignant skin growths.

Hereditary cancer genes

Genes like BRCA2 (breast cancer) or MSH2 and MLH1 (colorectal cancer) which, when mutated, affect DNA repair mechanisms.