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Related Concept Videos

Nucleotide Excision Repair01:08

Nucleotide Excision Repair

Overview
Mutations01:39

Mutations

Overview
Mutations01:35

Mutations

Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. Mutations can be characterized in a number of different ways: whether and how they alter the amino acid sequence of the protein, whether they occur over a small or large area of DNA, and whether they occur in somatic cells or germline cells.
Chromosomal Alterations Are Large-Scale Mutations
While point mutations are changes in a single nucleotide in...
Nucleotide Excision Repair01:38

Nucleotide Excision Repair

DNA Distortion and Damage
Cells are regularly exposed to mutagens—factors in the environment that can damage DNA and generate mutations. UV radiation is one of the most common mutagens and is estimated to introduce a significant number of changes in DNA. These include bends or kinks in the structure, which can block DNA replication or transcription. If these errors are not fixed, the damage can cause mutations, which in turn can result in cancer or disease depending on which sequences are...
Spontaneous and Induced Mutations01:30

Spontaneous and Induced Mutations

Spontaneous mutations arise infrequently during DNA replication due to errors in the process. A key factor behind these errors is tautomeric shifts in nitrogenous bases, where bases transition from keto to enol forms or amino to imino forms. This shift can alter base-pairing rules, leading to mutations. Additionally, reactive oxygen species (ROS) arising from aerobic metabolism can damage DNA, resulting in depurination (loss of a purine base) or depyrimidination (loss of a pyrimidine base).
Other Unique Bacteria01:18

Other Unique Bacteria

Magnetic bacteria exhibit a directed movement called magnetotaxis, driven by structures called magnetosomes. These magnetosomes consist of chains of magnetic particles made of either magnetite (Fe₃O₄) or greigite (Fe₃S₄) and are organized in a linear conformation by a protein scaffold within invaginations of the cell membrane. The bacteria align along the north–south magnetic field lines, much like a compass needle. They are typically microaerophilic or anaerobic and are commonly found near the...

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Related Experiment Video

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Measuring DNA Damage and Repair in Mouse Splenocytes After Chronic In Vivo Exposure to Very Low Doses of Beta- and Gamma-Radiation
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Mutation induction in human cells after low dose X ray exposure.

F Yatagai1, S Morimoto, S Goto

  • 1Radioisotope Technology Division, Cellular Physiology Laboratory, Institute of Physical and Chemical Research, Wako-shi, Saitama 351-0198, Japan. yatagai@postman.riken.go.jp

Radiation Protection Dosimetry
|August 27, 2002
PubMed
Summary

Low dose X-ray radiation significantly increased DNA double-strand break repair via end-joining, leading to loss of heterozygosity in human cells, despite no significant mutation increase at the thymidine kinase locus.

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Area of Science:

  • Radiation biology
  • Molecular genetics
  • Cellular response to DNA damage

Background:

  • Low dose ionizing radiation (IR) effects are crucial for radiation risk assessment and understanding cellular mechanisms.
  • The thymidine kinase (TK) locus in human lymphoblastoid cells is a sensitive target for mutation analysis.
  • Loss of heterozygosity (LOH) is a key indicator of DNA repair pathway activation.

Purpose of the Study:

  • To investigate the impact of low dose X-ray exposure on mutation and LOH at the TK locus in human lymphoblastoid cells.
  • To determine if low dose IR influences DNA double-strand break repair mechanisms, specifically end-joining.
  • To correlate observed LOH events with cellular responses to low dose radiation.

Main Methods:

  • Irradiation of human lymphoblastoid TK6-20C cells with 100 mGy of X rays.
  • Selection of TK mutants resistant to trifluorothymidine (TFT).
  • Molecular analysis of TK mutants to assess loss of heterozygocity (LOH), distinguishing hemizygous-LOH.

Main Results:

  • A 100 mGy X-ray dose did not significantly increase overall mutation frequency at the TK locus.
  • However, the fraction of hemizygous-LOH among TK mutants increased significantly from 10% to 42% after 100 mGy X-ray exposure.
  • This observed increase in hemizygous-LOH is consistent with previous findings at higher doses (2 Gy) and suggests activation of DNA double-strand break repair.

Conclusions:

  • Low dose X-ray radiation (100 mGy) significantly enhances DNA double-strand break repair via end-joining, manifesting as increased hemizygous-LOH.
  • While not significantly increasing point mutations, low dose IR clearly impacts DNA repair pathways at the molecular level.
  • The study highlights LOH as a sensitive biomarker for detecting cellular responses to low dose ionizing radiation.