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Related Concept Videos

Phase II Reactions: Methylation Reactions01:17

Phase II Reactions: Methylation Reactions

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Methylation is a phase II biotransformation process involving the attachment of a methyl group to a substrate. Enzymes known as methyltransferases orchestrate this reaction.
The mechanism of methylation unfolds in two stages. The first stage sees a methyltransferase enzyme facilitating the transfer of a methyl group from S-adenosylmethionine (SAM) to the substrate, forming S-adenosylhomocysteine (SAH). The second stage involves further metabolism of SAH into homocysteine, which can be recycled...
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Epigenetic changes alter the physical structure of the DNA without changing the genetic sequence and often regulate whether genes are turned on or off. This regulation ensures that each cell produces only proteins necessary for its function. For example, proteins that promote bone growth are not produced in muscle cells. Epigenetic mechanisms play an essential role in healthy development. Conversely, precisely regulated epigenetic mechanisms are disrupted in diseases like cancer.
X-chromosome...
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Epigenetic mechanisms play an essential role in healthy development. Conversely, precisely regulated epigenetic mechanisms are disrupted in diseases like cancer.
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Nucleic acid biosynthesis is a fundamental biochemical process that produces the purine and pyrimidine nucleotides essential for DNA and RNA synthesis. This pathway maintains a balanced nucleotide pool, preventing imbalances that could jeopardize genetic integrity and cellular function. Given the crucial role of nucleotides, their synthesis is tightly regulated to ensure proper cellular homeostasis.Purine BiosynthesisThe biosynthesis of purine nucleotides begins with ribose-5-phosphate, a...
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Mutagenicity and Carcinogenicity01:25

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Mutagenicity and carcinogenicity refer to the ability of drugs to cause genetic defects and induce cancer, respectively. The International Agency for Research on Cancer (IARC) classifies agents into four groups based on their carcinogenic potential. Group 1 agents are known human carcinogens; group 2A agents are probably carcinogenic to humans; group 3 agents lack data to support their role in carcinogenesis; and group 4 includes agents for which data support that they are not likely to be...
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Mismatch Repair01:20

Mismatch Repair

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Organisms are capable of detecting and fixing nucleotide mismatches that occur during DNA replication. This sophisticated process requires identifying the new strand and replacing the erroneous bases with correct nucleotides. Mismatch repair is coordinated by many proteins in both prokaryotes and eukaryotes.
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Updated: Dec 21, 2025

Continuous Fluorescence-Based Endonuclease-Coupled DNA Methylation Assay to Screen for DNA Methyltransferase Inhibitors
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Biological Basis for Threshold Responses to Methylating Agents.

Adam D Thomas1

  • 1Centre for Research in Biosciences, University of the West of England, Frenchay Campus, Bristol BS16 1QY, United Kingdom.

Chemical Research in Toxicology
|May 12, 2020
PubMed
Summary
This summary is machine-generated.

Cellular responses to methylating agents depend on DNA repair capacity and the DNA damage response (DDR). Understanding damage thresholds is key to predicting chemical toxicity and cell fate.

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Area of Science:

  • Toxicology
  • Molecular Biology
  • Genetics

Background:

  • Cellular outcomes of chemical exposure involve both chemical effects and cellular responses.
  • Understanding genotoxic interactions between chemistry and biology is advancing, revealing links between mutation induction and cellular repair capacity.
  • The toxicity pathway from chemical exposure to cell death involves multiple endpoints beyond simple mutation induction.

Purpose of the Study:

  • To explore the possibility of dose and damage thresholds for methylating agents.
  • To investigate the role of cellular repair and response mechanisms in determining cell fate after chemical exposure.
  • To examine the underlying evolutionary mechanisms that may account for these thresholds.

Main Methods:

  • Review of existing data on methylating agents, DNA adducts, and cellular responses.
  • Analysis of the interplay between mutagenic and clastogenic events induced by methylating agents.
  • Examination of the DNA damage response (DDR) pathways, including homologous recombination and nonhomologous end joining.

Main Results:

  • Methylating agents can be mutagenic, with potency influenced by methylguanine DNA-methyltransferase (MGMT) repair capacity.
  • Mutagenic adducts can be converted to clastogenic events (double-strand breaks) through erroneous biological processing.
  • Cell fate (repair, death, senescence) is determined by the extent of DNA damage and the strength of the DDR signaling cascade.

Conclusions:

  • Cellular fate thresholds likely exist, dependent on specific repair and response mechanisms to methyl adducts.
  • Quantifying these thresholds could elucidate the proportion of adducts that are mutagenic, clastogenic, and ultimately toxic.
  • Further research is needed to fully resolve the molecular mechanisms by which methyl adducts induce cell death.