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HSC Biology

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Lesson 18, Topic 1
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Operation of Mutagens

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Electromagnetic Radiation

Waves which carry electromagnetic energy.

  • When ER waves move through matter, they give energy to the atoms they hit.
  • The atoms are ‘hyped up’ by extra energy, causing them to vibrate and lose electrons.
  • Chemical bonds break from the vibration and loss of electrons. In DNA, the backbone can break and split or the bases might rebind to the wrong ones.
  • If this occurs, the cell can be so damaged that it dies. The cell may survive, yet some or all of its DNA will be mutated.


  1. The ​sun​ is the biggest source of EM radiation in everyday life-> impossible to avoid. It emits infrared, visible & ​UV light-> dangerous (mutagen)-> formation of pyrimidine dimers.
  2. Radioactive elements​ ​are another source of EM radiation, Eg Uranium-236. They release gamma rays as they decay (made by chemistry labs and nuclear).
  3. Medical imagery machines​-> Eg, X-ray machines, PET scans. X-ray radiation can alter the nitrogenous base sequence of DNA-> insertion or translocation mutations.


  • Different chemicals cause mutations in different ways
  • Alter the nitrogenous base sequence ​of DNA
  • Chemical mutations cause a change in DNA that alters the function of proteins and, as a result, cellular processes are impaired
  • Chemical mutagens:
    • Incorporate themselves into the DNA
    • Insert themselves into DNA
    • Makes gaps in DNA
  • Examples of chemical mutagens
    • Ingested chemicals​ including ​alcohol, tar in tobacco smoke, some medications and chemicals in food​ – especially charred and fatty foods, and food additives and preservatives (such as nitrites)
    • Environmental irritants and poisons​ such as organic solvents (for example, benzene), cleaning products, asbestos, coal tars, pesticides and some hair dyes.
  • Chemicals that are mutagenic are similarly structured to normal bases in DNA and so they may mistakenly become incorporated into DNA during replication. (DNA polymerase is ‘tricked’)
  • This results in the ​insertion​ of incorrect nucleotides opposite them during replication- termed ​mispairing
  • Their insertion often results in the productions of a non-functional protein end product Some examples of molecules that are chemical mutagens include:
    • Agent Orange

Naturally-Occurring Mutagens

  • Naturally occurring mutagens are mutagenic agents that are present at normal levels within natural environments, and may cause mutations
  • Chemicals which specifically come from microbes, plants and animals
  • The likelihood of mutation is thought to increase wth increased frequency and length of exposure
  • Can be biological or non-biological
  • Non-biological​ naturally occurring mutagens include metals, eg mercury, that occur naturally in the environment
  • Biological​ naturally occurring mutagens include viruses, bacteria, fungi and their products

Biological Mutagens and their Actions

End-products of metabolism:​ many naturally occurring biological mutagens may be produced by fungi or plant or animals cells during metabolism. EG, nitrosamine (chemicals found in stomach when certain foods are eaten in combination) such as certain processed and smoked meats and sausages.

Microbes a​ re naturally occurring​ biological mutagens.​ These include ​viruses​ (eg Hepatitis B virus, HIV, Rubella virus), and ​bacteria.​ Mutagenic microbes may also directly alter the genetic material in cells.

Effects of Biological Mutagens

Mutagenic microbes are able to insert their own base sequence into DNA and in this way change the functioning of genes and trigger cancers.