BIO 09: Module 6 Reviewer - Gene Mutation, DNA Repair, and Transposition

Vocabulary flashcards reviewing concepts in gene mutations, functional classifications, human single-gene diseases, DNA repair pathways, the Ames test, and transposable elements based on Module 6.

Central Dogma

The core framework of molecular biology: DNA undergo transcription to form mRNA, rRNA, and tRNA, which interact at the ribosome to undergo translation into protein.

Gene Mutation

Any base pair change in a part of DNA that causes an alteration of the nucleotide sequence of an organism's genome.

Germ-Cell Mutations

Mutations occurring in germ cells that can be inherited by offspring and serve as the foundation of genetic diversity and evolution.

Point Mutation

A base substitution in which one base pair in a DNA molecule is changed to another.

Missense Mutation

A point mutation within a protein-coding region that changes a single nucleotide in a triplet, creating a new codon that codes for a different amino acid.

Nonsense Mutation

A point mutation that converts an amino acid codon into a stop codon, causing premature termination of protein synthesis.

Silent Mutation

A point mutation that alters a codon sequence but does not change the amino acid coded for at that position.

Neutral Mutation

A mutation occurring in noncoding DNA that does not affect gene products or gene expression.

Transition Mutation

A point mutation in which a pyrimidine replaces a pyrimidine (C ⇄ T) or a purine replaces a purine (A ⇄ G).

Transversion Mutation

A point mutation in which a purine replaces a pyrimidine, or a pyrimidine replaces a purine.

Frameshift Mutation

The insertion or deletion of one or more nucleotides at any point within a gene, shifting the reading frame and altering all subsequent downstream three-letter codons.

Loss-of-Function Mutation

A mutation that reduces or completely eliminates the normal function of the gene product.

Null Mutation

A type of loss-of-function mutation resulting in a complete loss of gene function.

Gain-of-Function Mutation

A mutation that codes for a gene product with enhanced, negative, or entirely new functions.

Suppressor Mutation

A second mutation that counteracts, reverts, or relieves the functional effects of a previously occurring mutation.

Intragenic Suppressor Mutation

A suppressor mutation that occurs within the same gene as the initial mutation.

Intergenic Suppressor Mutation

A suppressor mutation that occurs in a different gene from the initial mutation.

Conditional Mutation

A mutation whose phenotypic effect is manifested only under specific environmental conditions, such as temperature-sensitive coat color in Siamese cats and Himalayan rabbits.

Spontaneous Mutation

A nucleotide sequence change occurring naturally as a result of normal biological or chemical processes without specific external agents.

Mutation Rate

The probability that a gene will undergo a mutation in a single generation or during the formation of a single gamete.

Tautomers

Alternate chemical forms of nitrogenous bases (e.g., enol, imino) that alter hydrogen bonding capabilities and increase mispairing during DNA replication.

Replication Slippage

An error during replication where one DNA strand loops out and is displaced, causing DNA polymerase to slip or stutter and create insertions or deletions.

Depurination

A spontaneous DNA lesion involving the loss of an adenine (A) or guanine (G) nitrogenous base.

Deamination

A spontaneous chemical change converting cytosine to uracil, or adenine to hypoxanthine.

Induced Mutation

A mutation caused by the influence of exogenous physical or chemical factors, such as UV light inducing skin cancer.

Base Analogs

Chemical mutagens, such as 5-bromouracil, that substitute for purines or pyrimidines during DNA synthesis.

Alkylating Agents

Chemical mutagens, such as mustard gases and ethylmethane sulfonate (EMS), that donate an alkyl group ($\text{CH}_3$ or $\text{CH}_2\text{CH}_3$) to amino or keto groups in nucleotides.

Intercalating Agents

Chemical compounds, such as ethidium bromide, that wedge between base pairs in DNA, distorting the helix and causing frameshift mutations.

Adduct-Forming Agents

Chemical agents, such as acetaldehyde from cigarette smoke, that covalently bind to DNA, altering its conformation and interfering with replication and repair.

OMIM (Online Mendelian Inheritance in Man)

A comprehensive online database cataloging human genes, mutations, and inherited genetic disorders.

Achondroplasia

A single-gene disorder caused by a missense mutation resulting in a glycine to arginine replacement at position 380 of the FGFR3 gene.

Marfan Syndrome

A single-gene disorder caused by a nonsense mutation replacing tyrosine with a STOP codon at position 2113 of the fibrillin-1 gene.

Familial Hypercholesterolemia

A single-gene disorder caused by various short insertion mutations throughout the LDLR gene.

Cystic Fibrosis

A monogenic disease commonly caused by a three-base-pair deletion of the phenylalanine codon at position 508 of the CFTR gene.

Huntington Disease

An inherited neurodegenerative disorder caused by a trinucleotide repeat expansion of $\ge 40$ (CAG) repeats in the coding region of the huntingtin gene.

$\beta$-Thalassemia

An inherited autosomal recessive blood disorder resulting from mutations in the HBB gene, which encodes the 146-amino acid $\beta$-globin polypeptide.

Fragile-X Syndrome

A genetic disease caused by trinucleotide repeat expansion that represents one of the most common causes of inherited intellectual disability.

Myotonic Dystrophy

A disorder caused by trinucleotide repeat expansion leading to progressive muscle wasting and weakness.

DNA Polymerase III Proofreading

A repair mechanism where DNA polymerase III uses its $3' \rightarrow 5'$ exonuclease activity to reverse direction, remove mispaired nucleotides, and catch 99% of replication errors.

Mismatch Repair (MMR)

A post-replication repair pathway that detects and corrects base-base mismatches and small insertions or deletions that escape proofreading.

Postreplication Repair

A repair process directed by the RecA protein that utilizes recombinational exchange to fill unreplicated gaps left when DNA polymerase stalls and skips over a lesion.

Photoreactivation Repair

A light-dependent repair mechanism in which photoreactivation enzyme (PRE) or photolyase uses visible blue light to cleave cross-linking bonds in pyrimidine dimers.

Base Excision Repair (BER)

A cut-and-paste repair pathway that removes incorrect base pairings resulting from chemically modified bases or uracil produced by cytosine deamination.

Nucleotide Excision Repair (NER)

An excision repair system governed by roughly 30 genes in eukaryotes that removes bulky lesions, such as pyrimidine dimers, that distort the double helix.

Xeroderma Pigmentosum (XP)

A recessive genetic disorder caused by defects in NER pathways, leading to extreme sensitivity to UV light and a 2000-fold increase in skin cancer risk.

Ames Test

A biological assay invented by Bruce Ames in the 1960s using a histidine-requiring (his⁻) strain of Salmonella and rat liver extract to test the mutagenic potential of chemical compounds.

Transposable Elements (TEs)

DNA sequences ranging from 50 to 10,000 base pairs that can move (transpose) within and between chromosomes.

DNA Transposons

Transposable elements that move via a cut-and-paste mechanism without an RNA intermediate, requiring inverted terminal repeats (ITRs) and the enzyme transposase.

Retrotransposons

Transposable elements that move and amplify via a copy-and-paste mechanism using an RNA intermediate, structurally resembling non-infective retroviruses.