The Basics of Molecular Biology by Alexander Vologodskii

Author:Alexander Vologodskii
Language: eng
Format: epub
ISBN: 9783031194047
Publisher: Springer International Publishing

The most dangerous chemical damage to DNA is the double-stranded break. In this case, there is no intact template for the repair. The breaks are caused by ionizing radiation, various chemical reagents, and replication errors. The main system which repairs double-stranded breaks simply joins the newly formed ends of the double helix. Since the ends are usually damaged, rejoining them requires removing a few nucleotides at the ends. Therefore, this way of repair results in a loss of 1–3 base pairs at the repair site. Of course, this is a very serious and potentially damaging mutation. It seems that such lesions do not happen too often, although the issue requires further investigation.

There is another, more complex but accurate way to repair double-stranded breaks. During a relatively short period of cell life, each chromosome is represented by two identical sister chromatids. This is a period after DNA replication but before cell division. If a double-stranded break happens in this period, the intact sister chromatid can be used as a template to repair the broken one. The corresponding chain of reactions represents an example of homologous recombination. Homologous recombination is not just a repair mechanism for double-stranded breaks. It also allows the exchange of double-stranded DNA segments between the pairs of homologous chromosomes. This recombination is a very complex process involving many enzymes. We will not discuss its details here.

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