The DNA consists of a double strand and is continuously multiplied. This process is called DNA replication. This can lead to errors that need to be repaired. This is just one reason for possible DNA damage. External effects such as UV radiation can also damage the DNA. This then leads to mutations that affect the proteins produced. They lose their function or become too active, they can no longer reach their destination in the cell or they can no longer be broken down by the cell when the protein is no longer needed.
There are different DNA repair mechanisms. Which mechanism comes into effect depends on the type of DNA damage. This can be the repair of a single strand or a double strand break as well as the repair of individual bases.
The repair is performed by enzymes that rejoin the DNA during a break. These are ligases. The exchange of bases is carried out by recombinases and polymerases. DNA helicases serve to unwind the DNA. They prepare the affected DNA sections for repair.
With a break in DNA, various repair mechanisms can come into effect. These mechanisms are referred to as homologous or non-homologous recombination.
Recombination occurs not only in DNA damage, but also in reproduction when it comes to recombination of DNA from both partners and embryo development. This recombination is then referred to as sexual recombination. Homologous recombination to remove DNA damage results in the assembly of two similar, homologous DNA strands. Subsequently, a pairing of the DNA strands and a certain DNA section is exchanged between the two strands. Meanwhile, the so-called "Holliday structure" of DNA is formed. This process of exchange is carried out by special enzymes, the recombinases.
A break can also be done by directly linking two DNA ends. In this case, there is no homologous sequence, whereby a gap in the DNA must be filled in between two ends to create the missing homologous region. This is called "Synthesis dependent strand-annealing" and DNA polymerases fill in the gaps.
Another way to repair them is to shorten two ends until they can be rejoined so that the areas fit together. This is the "single beach annealing". As a result, short areas of DNA are lost. This repair is performed by the nucleotide excision repair system.
Non-homologous repair processes are performed independently of matching DNA sequences. Two major repairs are distinguished. Non-homologous end-joining directly links two DNA duplexes by the enzyme ligase. This repair does not require a homologous sequence, as a guide, compared to the other procedures mentioned, to provide as few errors as possible in the DNA after repair.
Another process of DNA repair is "microhomology-mediated end-joining". This leads to the deletion, the removal of DNA areas. Again, no guidance is used. This repair is considered very prone to error and is often the reason for the development of mutations.
Erroneous DNA repair produces a variety of diseases, the specificity of which depends on which DNA region and which genes are affected by these defects. One group of such diseases is called chromosome breakage syndrome. In doing so, breaks in DNA packed in chromosomes are not properly repaired, and these fractures are more common than normal.
This type of disease is inheritable. A well-known disease of this group is the Werner syndrome. This is an autosomal recessive disease, ie the mutation that causes this disease is located on one of the autosomes, one of the chromosomes (excluding the sex chromosomes). It is recessive and less likely to have an effect on the phenotype than a dominant gene mutation. Werner syndrome mainly affects the mesodermal tissue. There is an increased aging of the affected person after puberty.
Another disease in the category of chromosome fracture syndromes is the Louis Bar syndrome. It is also an autosomal recessive disease. There is a high number of different symptoms in this disease. These can be explained by the fact that a gene is affected, which recognizes DNA damage by UV rays and is also involved in the regulation of the DNA repair. It comes to neurological defects, as well as an impairment of the immune system. The consequences are a number of other diseases such as pneumonia.
Furthermore, the disease Xeroderma pigmentosum is a disease that can be counted to this class. It is a disease of the skin. The affected persons are also known as moonshine children. Genes that encode enzymes of the DNA repair mechanism are affected by defects. It comes to impaired skin by UV radiation, which lead to the formation of tumors of the skin. Those affected must avoid daylight, which affects the entire rhythm of life.Tags: