What are the classifications of mutagens?

Mutagens may be classified as physical, chemical or biological agents.  

Physical mutagens

Heat and radiation are the two most notable mutagens:

• Heat: DNA is sensitive to high heat. Temperatures above 95°C cause the phosphodiester bonds in DNA to break, which results in breakage of the DNA strand. 
• Radiation: Radiations such as X-rays, UV rays, neutrons, and alpha rays directly damage the DNA or the nucleotides in different ways. 

Chemical mutagens

The three main chemical mutagens are alkylating agents, intercalating agents, metal ions, and base analogs. 

• Alkylating agents: Alkylating agents introduce alkyl groups in DNA, which increases ionization and causes base-pairing errors, eventually creating gaps within the DNA strand. 
• Intercalating agents: These mutagens insert themselves in the DNA helix, eventually interfering with the transcription, replication, and translation, usually resulting in frameshift mutation. 
• Metal ions: Metal ions promote DNA damage and hinder the DNA repair process by generating reactive oxygen species (ROS), which causes DNA hyper-methylation. 
• Base analogs: These mutagens are structurally similar to the DNA bases – pyrimidines and purines. Because of these structural similarities, base analogs get incorporated into the structure of the DNA during the replication process. This alters the DNA sequence, causing a mutation. 

Biological mutagens

Biological mutagens include transposons and insertion sequences, viruses, and bacteria. 

• Transposons and insertion sequences: These DNA units autonomously relocate or multiply DNA fragments. Both transposons and insertion sequences move within the DNA, disrupting gene functionality upon insertion. These elements encode the information for the enzyme transposases, which creates new transposition sites in the DNA.
• Viruses: Viruses have the potential to interfere with genetic function by inserting their DNA into the genome. Some viruses, such as the Rous sarcoma virus, have been documented to trigger cancer, indicating that viruses possess mutagenic properties.
• Bacteria: Certain inflammation-inducing bacteria such as Helicobacter pylori produce reactive oxygen species that results in DNA damage and impaired DNA repair mechanisms, which increases the likelihood of mutations occurring.