Mutagens are the substances or agents that induces heritable change led in cells or organisms. Mutagenesis is the processes that result in genetic change.
A mutation is any change in a cell or in an organism that is transmitted to subsequent generations. Mutations can occur spontaneously or be induced by chemical or physical agents. The cause of mutations is usually some form of damage to DNA or chromosomes. However, damage can occur in a segment of DNA that is a non-coding region and thus will not result in a mutation. Mutations may or may not be harmful. They may occur in either somatic or germ cells, Mutations that occur in germ cells may be transmitted to subsequent generations. There are two types of mutagens: Chemical and physical mutagens
(a) Chemical Mutagens
Chemical mutagens are
- Nitrosoguanidine (NTG)
- Base Analogs (e.g. BrdU)
- Simple Chemicals (e.g. acids)
- Alkylating Agents (e.g. N-ethyl-N-nitrosourea (ENU): These agents can mutate both replicating and non-replicating DNA. In contrast, a base analog can only mutate the genetic material (DNA) when the analog is incorporated in replicating the DNA. Each of these classes of chemical mutagens has certain effects that then lead to transitions, transversions, or deletions.
- Methylating agents (e.g. ethane methyl sulfonate (EMS))
- Polycyclic hydrocarbons (e.g. benzpyrenes found in internal combustion engine exhaust)
- DNA intercalating agents (e.g. ethidium bromide)
- DNA crosslinker (e.g. platinum)
- Oxidative damage caused by oxygen radicals.
B) Physical Mutagens
Physical mutagens are non-ionizing and ionizing radiations:
Ultraviolet Radiation (Non-ionizing Radiation): These radiations excite electrons to a higher energy level. DNA absorbs ultraviolet light. Two nucleotide bases in DNA – cytosine and thymine-are most vulnerable to excitation that can change base- pairing properties. UV light can induce adjacent thymine bases in a DNA strand to pair with each other, as a bulky dimer.
Ionizing Radiation: These radiations are X- rays, gamma rays etc. DNA has so-called hotspots, where mutations occur up to 100 times more than the normal mutation rate. A hotspot can be at an unusual base, e.g., 5-methylcytosine. Ionizing radiations attacks on these hotspot and break the DNA.