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Molecular medicine-The DNA Damage Theory of Aging

Occurrence of Dna Damage and Pathways
of DNA Repair
Except for certain viruses with an RNA
genome, the genomes of most organisms
are composed of DNA. If DNA damage is
the cause of aging, thenDNAdamage is expected
to occur frequently in multicellular
organisms. Table 1 lists some important
types of DNA damage caused by normal
metabolic processes in mammals. These
data suggest, for instance, that in the rat at
least 95,000 DNA damages of various types
occur, averaged over all cell types, per cell
per day. The majority of these damages
alter the structure of only a single DNA
strand, so the redundant information in
the complementary strand can usually be
used to repair the damage. The damages
shown in Table 1 are the newly occurring
damages, most being rapidly repaired.
Five major DNA repair pathways known
to be utilized by cells to repair the damages
indicated in Table 1 are as follows:
• Nucleotide excision repair (NER) [with
two subpathways, largely using the
same enzymes: transcription coupled
repair (TCR) and global genomic repair
(GGR)]
• Base excision repair (BER)
• Nonhomologous end joining (NHEJ)
• Homologous recombinational repair
(HRR)
• O6-methylguanine-DNA methyltransferase
(MGMT)



This post first appeared on Hope For A Child, please read the originial post: here

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Molecular medicine-The DNA Damage Theory of Aging

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