University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

486

Pages:

2
Author:

Mariam A. A.

Chemical and Biological Mutagens Chemical Mutagens • • • • • Chemical mutagens are chemical substances that, when exposed to them, they have the capacity to give rise to mutation Chemical mutagens can alter the nitrogenous base sequence of DNA Some chemical mutagens may insert themselves between nitrogenous bases in the middle of a DNA double helix whereby during DNA replication. This effectively distorts the double helix at the position where the position mutagen is inserted. This results in wrong nitrogenous bases being complementary paired to template strand and the chemical substance may be mistaken as a nitrogenous base during the replication process. Example One: Nitrous acid is a chemical mutagen has the capable to interact with DNA and swap a nitrogenous base with another: - Cytosine may be swapped with uracil such that, during DNA replication, adenine is bonded to uracil instead of guanine. Also, in this case, uracil is now present in the DNA sequence which normally it is not. ✓ This effectively has alters the mRNA sequence during protein synthesis which may lead to the specification of a different amino acid sequence in the resultant polypeptide chain. ✓ Sometimes, there are silent mutation. This is because in silent mutations, although the mRNA sequence is altered, the amino acid sequence is unchanged due to the codon degeneracy nature of the translation table. Example Two: Benzopyrene is a chemical mutagen and a hydrocarbon present in cigarette smoke that is capable of being inserted between nitrogenous bases, effectively distorting the DNA double helix at the position where benzopyrene is added. This causes wrong nitrogenous bases being complementary paired to template strands during DNA replication. - This effectively alters the mRNA sequence during protein synthesis which may lead to the specification of a different amino acid sequence in the resultant polypeptide chain. Draw a mind map summarizing the above information Naturally Occurring Mutagens • • • • Naturally occurring mutagens can be biological (‘living’) or non-biological (‘non-living’) in nature. In both case, these mutagens are classified as naturally occurring because they exist at natural environments. Biological mutagens can be substances that are formed as by-products of natural metabolic chemical reactions. - For example, cycasin is a naturally occurring biological mutagen that is produced and present in the Australian Macrozamia plant. Biological mutagen is dimethylnitrosamine which is produced as a by-product in many animals from the chemical reaction between food containing nitrite and amines. Non-biological mutagens include those that are not living or not produced by living organisms. Chromium is a metal and a non-biological mutagen that can be found naturally in sedimentary rocks. Water can dissolve chromium in waterways which end up in potable water. However, in our potable water, chromium exist in trace quantities (0.1 milligram per litre) that is unable to cause any biological harm.