DNA synthesis involved in DNA repair

Definition

Target type: biologicalprocess

Synthesis of DNA that proceeds from the broken 3' single-strand DNA end and uses the homologous intact duplex as the template. [PMID:10357855]

DNA repair is a fundamental cellular process that maintains the integrity of the genome by correcting errors or damage that occur in DNA molecules. DNA synthesis plays a crucial role in this repair process, ensuring the accurate replication of the damaged or missing sequences.

Here is a detailed description of the biological process of DNA synthesis involved in DNA repair:

1. **Damage Recognition:** Specialized proteins, known as DNA repair enzymes, scan the genome for any abnormalities, such as double-strand breaks, single-strand breaks, base modifications, or cross-links. These proteins identify the damaged region and recruit other repair machinery.

2. **Excision Repair:** In many repair pathways, the damaged section of DNA is excised by specialized nucleases. For instance, in base excision repair (BER), a damaged base is removed by DNA glycosylase enzymes, creating an apurinic/apyrimidinic (AP) site. In nucleotide excision repair (NER), a larger segment of DNA containing the damage is removed by a complex of proteins.

3. **Gap Filling:** Once the damaged DNA is removed, the gap created needs to be filled with new, correct DNA sequences. This is where DNA synthesis comes in.

4. **DNA Polymerase Activity:** DNA polymerases, specialized enzymes, are responsible for synthesizing new DNA strands. They use the intact complementary strand as a template to create a new strand that is identical to the original. DNA polymerases add nucleotides to the 3' end of a growing DNA strand, using the base pairing rules (A with T and C with G).

5. **Primer Requirement:** DNA polymerases can only extend existing DNA strands, they cannot initiate synthesis de novo. Therefore, a short RNA primer (a short sequence of nucleotides) is synthesized by an enzyme called primase, which provides a 3' end for DNA polymerase to start adding nucleotides.

6. **Ligase Action:** Once the gap is filled, the newly synthesized DNA strand is joined to the existing DNA strand by DNA ligase. This enzyme seals the remaining nick in the DNA backbone, restoring the integrity of the DNA molecule.

7. **Repair Pathway Specificity:** Different DNA repair pathways utilize specific DNA polymerases with different properties. For example, in BER, DNA polymerase β is involved in filling small gaps, while in NER, DNA polymerase δ or ε are involved in filling larger gaps.

8. **Error Prone Polymerases:** Some DNA polymerases, known as "error-prone polymerases," are utilized in situations where DNA damage is extensive or when accurate replication is not possible due to cellular stress. These polymerases can tolerate more mismatches and can even synthesize DNA across damaged regions, although with a higher error rate.

In conclusion, DNA synthesis plays a critical role in DNA repair by precisely filling gaps created by the removal of damaged DNA sequences. This process ensures the integrity of the genome, preventing mutations, and maintaining cellular function and survival.'
"

Proteins (7)

Compounds (55)