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Chapter 15: Problem 27

Why would a mutation in a mismatch repair gene lead to a mutator phenotype in a cell?

Short Answer

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Answer: A mutation in a mismatch repair gene can lead to a defective protein product that is unable to properly recognize and repair mismatches during DNA replication. This defect results in replication errors that go unrepaired before the cell divides, causing higher mutation rates in daughter cells and the development of a mutator phenotype. The mutator phenotype increases the likelihood of acquiring additional mutations, leading to genomic instability and higher chances of survival and adaptation under stress conditions or selective pressures. This phenotype critically influences the development of drug-resistant cancer cells and can contribute to tumor progression and metastasis.

Step by step solution

01

Introduction to Mismatch Repair Genes

Mismatch repair genes are responsible for repairing mismatches and other errors that occur during DNA replication. They maintain genetic stability and fidelity, ensuring that the newly replicated DNA strand matches the original template. Mutations in these genes can compromise their function and lead to an increased rate of errors during replication, which ultimately results in a mutator phenotype.
02

Understanding Mutator Phenotype

A mutator phenotype is a cellular state in which the rate of spontaneous mutations is significantly higher than in normal cells. This higher mutation rate increases the likelihood of acquiring genetic changes that could promote uncontrolled growth, genomic instability, or resistance to therapies in cancer cells.
03

Mutation in Mismatch Repair Gene

A mutation in a mismatch repair gene can lead to a defective protein product that is unable to properly recognize and repair mismatches during DNA replication. This defect can result in replication errors, deletions, or insertions that go unrepaired before the cell divides, leading to higher mutation rates in daughter cells and the development of a mutator phenotype.
04

Consequences of Mutator Phenotype

The mutator phenotype can have several consequences for the affected cell. As mentioned earlier, it can lead to genomic instability, which can result in a higher likelihood of acquiring additional mutations. This elevated mutation rate can lead to increased cell survival and adaptation under stress conditions or selective pressures by increasing the likelihood of acquiring advantageous mutations that enhance growth and fitness. For example, this phenotype plays a critical role in the development of drug-resistant cancer cells and can contribute to tumor progression and metastasis. In summary, a mutation in a mismatch repair gene can lead to a mutator phenotype in a cell, as the ability to recognize and repair mismatches during DNA replication is compromised, resulting in a higher mutation rate and increased genomic instability.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Mutator Phenotype
A mutator phenotype is an intriguing concept in genetics. It refers to a condition in which a cell has an increased rate of mutations compared to normal cells. This heightened mutation rate emerges due to defects in the DNA repair mechanisms, particularly those like mismatch repair that are crucial for maintaining genetic accuracy. Over time, such cells accrue genetic changes more rapidly, potentially leading to phenomena like cancer.

Cells with a mutator phenotype are prone to rapid evolution. This is because the ongoing mutations provide raw material on which natural selection can act.

Let's consider a few implications of this phenotype:
  • Increased genetic diversity within cell populations.
  • Higher chances of developing resistance to drugs, especially in cancer therapy.
  • Enhanced potential for cells to adapt to new and hostile environments, such as those created by therapeutic interventions.
The mutator phenotype is thus a double-edged sword: while it can promote survival under distress, it can also lead to rapid disease progression.
Genomic Instability
Genomic instability is closely tied to the mutator phenotype. It refers to an increased frequency of mutations within the genome, manifesting as a result of accumulated replication errors. When the machinery that repairs DNA, like mismatch repair, fails, genomic instability arises.

Here's how genomic instability impacts cells:
  • It can trigger the uncontrolled growth of cells, a hallmark of cancer.
  • Causes chromosomal rearrangements, amplifications, or even losses.
  • Leads to genetic heterogeneity in tumor tissues, complicating treatment.
Genomic instability effectively breaks the precision of cellular replication, giving rise to diverse clones within a single tumor. Such diversity can enhance the aggressiveness of tumors, allowing them to resist treatments and adapt to new challenges. Thus, managing genomic stability is crucial in medical interventions against cancer.
DNA Replication Errors
DNA replication is a vital cellular process that duplicates genetic material so that it can be passed on to daughter cells. However, this process is not foolproof, and errors do occur. Ideally, replication errors are corrected by systems like mismatch repair.

Replication errors include:
  • Mismatched base pairs, where incorrect nucleotide bases are incorporated.
  • Insertions or deletions of small sections of DNA, known as indels.
  • Slippage, which can affect repetitive DNA sequences leading to large-scale changes.
When mismatch repair is working properly, it identifies and corrects these errors, maintaining genetic integrity. However, defects in this system due to mutations can lead to a cascade of errors being transmitted to future generations of cells, fostering a mutator phenotype and genomic instability.

Therefore, the faithful execution of DNA replication is essential for life, and safeguarding against these errors is integral to preventing complex disorders like cancers.

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Most popular questions from this chapter

In this chapter, we focused on how gene mutations arise and how cells repair DNA damage. At the same time, we found opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, (a) How do we know that mutations occur spontaneously? (b) How do we know that certain chemicals and wavelengths of radiation induce mutations in DNA? (c) How do we know that DNA repair mechanisms detect and correct the majority of spontaneous and induced mutations?

Acridine dyes induce frameshift mutations. Why are frameshift mutations likely to be more detrimental than point mutations, in which a single pyrimidine or purine has been substituted?

Mutations in the \(I L 2 R G\) gene cause approximately 30 percent of severe combined immunodeficiency disorder (SCID) cases. These mutations result in alterations to a protein component of cytokine receptors that are essential for proper development of the immune system. The \(I L 2 R G\) gene is composed of eight exons and contains upstream and downstream sequences that are necessary for proper transcription and translation. Below are some of the mutations observed. For each, explain its likely influence on the \(I L 2 R G\) gene product (assume its length to be 375 amino acids). (a) Nonsense mutation in coding regions (b) Insertion in Exon 1 , causing frameshift (c) Insertion in Exon \(7,\) causing frameshift (d) Missense mutation (e) Deletion in Exon 2 , causing frameshift (f) Deletion in Exon 2 , in frame (g) Large deletion covering Exons 2 and 3

In which phases of the cell cycle would you expect doublestrand break repair and nonhomologous end joining to occur and why?

In maize, a \(D s\) or \(A c\) transposon can cause mutations in genes at or near the site of transposon insertion. It is possible for these elements to transpose away from their original site, causing a reversion of the mutant phenotype. In some cases, however, even more severe phenotypes appear, due to events at or near the mutant allele. What might be happening to the transposon or the nearby gene to create more severe mutations?
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