Biodiversity by R C Sobti

Author:R C Sobti
Language: eng
Format: epub
Publisher: CRC Press
Published: 2023-06-15T00:00:00+00:00

17.3 Overview of Genetic Repair Mechanisms

Genetic repair mechanisms are operative in living systems and are divided by the type of repair they perform in the cells. Broadly they are divided into (1) damage reversal and (2) damage removal. The genotoxicants cause lesions, and their repair systems are provided in Table 17.1.

TABLE 17.1 Genetic Repair Mechanisms DNA repair Systems Type of lesion Genotoxic source

* * *

(A) Damage reversal

Photo-reactivation Thymine dimmers UV radiation

Alkyltransferases (removal of alkyl groups) Alkylation Alkylating agents

(B) Damage removal

Base excision repair (BER) Oxidative lesions Reactive oxygen species (ROS)

Nucleotide excision repair (NER) Helix-distorting lesions UV radiation

uvrABC excision repair Cyclobutene pyrimidine dimers, DNA adducts UV radiation

Translesion synthesis Various lesions Various sources

Mismatch repair (MMR) Replication errors Replication

Single-strand-break repair (SSBR) Single-strand breaks (SSB) Ionizing radiation, ROS

Homologous recombination (HR) Double-strand breaks (DSB) Ionizing radiation, ROS

Non-homologous end joining (NHEJ) DSB Ionizing radiation, ROS

DNA inter-strand cross-link repair pathway Inter-strand cross-links Chemotherapy

Adaptive response SSB or DSB Base damages Alkylating agents, heat stress, oxidants, radiation, and heavy metals

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