If a DNA polymerase encounters a tautomeric shift during replication, determine the probability of a permanent base-pair substitution occurring in the next round of replication.

The rare tautomeric form allows abnormal pairing (e.g., A-C or G-T). During the first round, the wrong base is incorporated. In the subsequent round, this wrong base acts as the template for a new strand, resulting in a permanent transversion or transition mutation in 100% of the descendants of that specific DNA molecule.

Compare the functional outcome of a missense mutation versus a nonsense mutation regarding the final polypeptide chain length .

Missense: Substitutes one amino acid for another; the total number of amino acids remains identical to the wild-type. Nonsense: Converts a codon into a stop codon, causing premature termination and resulting in a truncated protein shorter than the original sequence.

Given a sequence 5'-ATG-CGT-TAA-3', predict the impact of a single nucleotide deletion after the first nucleotide on the reading frame .

The sequence shifts to 5'-AG TCG TTA A...-3'. This creates a frameshift mutation , altering every subsequent amino acid encoded by the gene, typically leading to a non-functional protein due to completely changed primary structure and potential premature termination.

Explain the relationship between depurination and the formation of an apurinic site .

Depurination is the spontaneous hydrolysis of the $N-\beta$-glycosyl bond between a purine base (Adenine or Guanine) and the deoxyribose sugar. This leaves a deoxyribose sugar without a base, known as an apurinic site (or AP site), which cannot specify a base pair during replication.

Distinguish the cellular role of Base Excision Repair (BER) from Nucleotide Excision Repair (NER) .

BER: Primarily repairs non-bulky damage like deaminated or oxidized bases using specific glycosylases to remove the damaged base. NER: Repairs bulky, helix-distorting lesions such as UV-induced pyrimidine dimers by removing a larger oligonucleotide segment surrounding the damage.

Explain the concept of anticipation in the context of trinucleotide repeat expansion disorders.

Anticipation refers to the clinical phenomenon where the symptoms of a genetic disorder become more severe or appear at an earlier age in successive generations. This occurs because the number of repeated units (e.g., CAG) tends to increase during gametogenesis due to DNA polymerase slippage .

Why is Non-Homologous End-Joining (NHEJ) considered a more error-prone pathway for repairing double-strand breaks compared to Homologous Recombination ?

Homologous Recombination uses the sister chromatid as a template to perfectly restore the sequence. In contrast, NHEJ directly ligates broken DNA ends together without a template, often resulting in the deletion or insertion of nucleotides at the break site.

Identify why somatic mutations occurring early in embryonic development have a more significant biological impact than those occurring in adult tissues.

Somatic mutations are not inherited. However, early embryonic mutations are propagated to a larger number of descendant cells (clonal expansion) during organogenesis, potentially affecting entire tissues or systems, whereas adult mutations are limited to a smaller local population of cells.

Describe the 'common theme' that turns a primary DNA lesion into a permanent genetic mutation .

A lesion creates a template error. During replication, DNA polymerase encounters the lesion and misincorporates a base. When the daughter strand serves as a template in the subsequent round of replication , the misincorporated base becomes a permanent, non-mutated sequence in the genome.

What is the specific utility of the Ames Test in evaluating potential chemical mutagens?

The Ames Test uses specific strains of Salmonella typhimurium (auxotrophic for histidine) to determine if a chemical can cause reversion mutations . If the bacteria revert to wild-type (histidine prototrophy) upon exposure, the chemical is identified as a mutagen .

Explain how intercalating agents like acridine orange induce frameshift mutations .

Intercalating agents possess planar structures that wedge between the stacked nitrogenous bases of the DNA double helix. This distortion causes DNA polymerase to skip or add an extra nucleotide during replication, resulting in insertions or deletions (indels) that shift the reading frame.

Analyze the consequence of a silent mutation occurring in the third position of a codon.

Due to the degeneracy of the genetic code (wobble position), changing the third nucleotide often codes for the same amino acid. Therefore, the primary protein structure remains unchanged , and the mutation typically has no phenotypic effect.

Determine why translesion synthesis (SOS repair) is categorized as a 'last resort' mechanism.

Translesion synthesis utilizes specialized, low-fidelity polymerases that lack proofreading capability. While these polymerases allow the replication fork to bypass a lesion and prevent cell cycle arrest , they do so by randomly inserting bases, significantly increasing the probability of mutagenesis .

If UV radiation causes a thymine dimer , which direct repair enzyme can fix the lesion without removing any nucleotides?

Photolyase . It binds to the thymine dimer and uses light energy to break the cyclobutane ring, restoring the original pyrimidine structures without excising any part of the DNA strand.

Compare germ-line mutations and somatic mutations regarding their contribution to evolution.

Germ-line mutations: Occur in gametes and are passed to the next generation, thus providing the raw material for evolution . Somatic mutations: Affect only the individual organism and are lost upon the death of the organism, having no contribution to the gene pool of future generations.

Molecular Mechanisms Of Dna Mutation And Cellular Repair Pathways Flashcards

Browse 1 flashcard sets with 15 cards for Molecular Mechanisms Of Dna Mutation And Cellular Repair Pathways in Stem. Study for free or create your own with AI.

1sets

15total cards

Flashcard Sets

Molecular Mechanisms of DNA Mutation and Cellular Repair Pathways

This deck explores the chemical basis of DNA damage, the molecular consequences of mutation types, and the sophisticated cellular repair mechanisms designed to preserve genomic integrity.

15 cards

intermediate

000

by @brad

Q: If a DNA polymerase encounters a tautomeric shift during replicati...

Q: Compare the functional outcome of a missense mutation versus a <st...

Q: Given a sequence 5'-ATG-CGT-TAA-3', predict the impact of a single nucleotide deletion</stro...

Create Molecular Mechanisms Of Dna Mutation And Cellular Repair Pathways flashcards with AI

Upload your Stem study materials and Evrika will generate flashcards automatically. Study smarter, not harder.

Get Started Free View Pricing