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In an animal different types of cells are distributed among different organs that have evolved different sensitivities to DNA damage. [ 65 ] In general global response to DNA damage involves expression of multiple genes responsible for postreplication repair , homologous recombination, nucleotide excision repair, DNA damage checkpoint , global ...
This type of DNA damage would not accumulate with age, since once a cell was lost through apoptosis, its double-strand damage would be lost with it. Thus, damaged DNA segments undermine the DNA replication machinery because these altered sequences of DNA cannot be utilized as true templates to produce copies of one's genetic material. [1]
DNA damage can be recognized by enzymes, and thus can be correctly repaired using the complementary undamaged strand in DNA as a template or an undamaged sequence in a homologous chromosome if it is available for copying. If a cell retains DNA damage, transcription of a gene can be prevented and thus translation into a protein will also be blocked.
Nucleotide excision repair (NER) is a particularly important excision mechanism that removes DNA damage induced by ultraviolet light (UV). UV DNA damage results in bulky DNA adducts — these adducts are mostly thymine dimers and 6,4-photoproducts. Recognition of the damage leads to removal of a short single-stranded DNA segment that contains ...
An arsenal of DNA repair mechanisms exists to repair various forms of damaged DNA and minimize genomic instability. Most DNA repair mechanisms require an intact DNA strand as template to fix the damaged strand. DNA damage prevents the normal enzymatic synthesis of DNA by the replication fork.
Ball and Stick Model of Double Helical DNA. A molecular lesion or point lesion is damage to the structure of a biological molecule such as DNA, RNA, or protein.This damage may result in the reduction or absence of normal function, and in rare cases the gain of a new function.
Breaks in DNA due to ionizing radiation can be repaired. New DNA synthesis by DNA polymerases is one of the ways radiation induced DNA damage can be repaired. However, DNA polymerases do not insert methylated bases which leads to a decrease in methylation of the newly synthesized strand.
These reactive chemical species can reach DNA by diffusion and the bimolecular reaction damages the DNA (oxidative stress). Unlike direct DNA damage which causes sunburn, indirect DNA damage does not result in any warning signal or pain in the human body. The bimolecular reactions that cause the indirect DNA damage are illustrated in the figure: