Thus, enzymes known as DNA glycosylases
remove damaged bases by literally cutting them out of the DNA strand through cleavage of the covalent bonds between the bases and the sugar-phosphate backbone
. The resulting gap is then filled by a specialized repair polymerase and sealed by ligase.
How is damaged DNA repaired?
Most damage to DNA is repaired by
removal of the damaged bases followed by resynthesis of the excised region
. Some lesions in DNA, however, can be repaired by direct reversal of the damage, which may be a more efficient way of dealing with specific types of DNA damage that occur frequently.
What enzyme helps in DNA repair?
DNA nucleases
catalyze the cleavage of phosphodiester bonds. These enzymes play crucial roles in various DNA repair processes, which involve DNA replication, base excision repair, nucleotide excision repair, mismatch repair, and double strand break repair.
How do enzymes repair cells?
The repair enzymes must detect the mismatched bases and repair the unmethylated strand before methylation of the new strand takes place.
The repair is initiated by a GATC endonuclease, which makes a single-strand cut in the strand bearing the incorrect base at the nearest GATC sequence
.
What is DNA damage and DNA repair?
At least five major DNA repair pathways—
base excision repair (BER), nucleotide excision repair (NER), mismatch repair (MMR), homologous recombination (HR) and non-homologous end joining (NHEJ)
—are active throughout different stages of the cell cycle, allowing the cells to repair the DNA damage.
What are the three major mechanisms of DNA repair?
There are three types of repair mechanisms:
direct reversal of the damage, excision repair, and postreplication repair
. Direct reversal repair is specific to the damage.
What are three ways that DNA gets damaged?
DNA damage occurs continuously as a result of various factors—
intracellular metabolism, replication, and exposure to genotoxic agents, such as ionizing radiation and chemotherapy
. If left unrepaired, this damage could result in changes or mutations within the cell genomic material.
What are the two types of DNA repair?
There are two general classes of DNA repair;
the direct reversal of the chemical process generating the damage and the replacement of damaged nucleotide bases
. DNA encodes the cell genome and is therefore a permanent copy of a structure necessary for the correct functioning of a cell.
What is direct repair of DNA?
Introduction. Direct repair is defined as
the elimination of DNA and RNA damage using chemical reversion that does not require a nucleotide template, breakage of the phosphodiester backbone or DNA synthesis
.
Which enzyme is used to join together two different types of DNA molecules?
DNA ligase
is a DNA-joining enzyme. If two pieces of DNA have matching ends, ligase can link them to form a single, unbroken molecule of DNA.
What are the types of DNA damages?
DNA damage can be subdivided into two types: (1) endogenous damage caused by reactive oxygen species (ROS) that are derived from metabolic byproducts and (2) exogenous damage caused by radiation (UV, X-ray, gamma), hydrolysis, plant toxins, and viruses.
