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Our DNA is constantly under attack from both internal and external factors, leading to various types of damage. Understanding how our cells combat this damage is crucial. So, what is base excision repair and what is it used for? It’s a vital cellular mechanism, a key DNA repair pathway that identifies and removes damaged or modified single bases from our DNA, ensuring genomic stability and preventing mutations.
Base Excision Repair The Cellular Cleanup Crew
Base excision repair (BER) is a fundamental pathway that cells use to correct small, non-bulky DNA lesions. These lesions often arise from oxidation, alkylation, deamination, or the spontaneous loss of a DNA base (depurination or depyrimidination). Think of it as a meticulous cleanup crew that patrols the DNA, identifying and removing damaged “building blocks” before they can cause serious problems. Its main goal is to maintain the integrity of the genetic code.
The BER pathway involves a series of enzymatic steps. First, a DNA glycosylase recognizes and removes the damaged base, creating an apurinic/apyrimidinic (AP) site (also known as an abasic site) which is essentially a “hole” in the DNA sequence. This AP site is then processed by an AP endonuclease, which cuts the DNA backbone next to the AP site. Following this, a DNA polymerase fills in the gap with the correct nucleotide, and finally, a DNA ligase seals the nick in the DNA strand.
There are two main pathways of BER: short-patch BER and long-patch BER. Which pathway is selected depends on the specific type of damage and the cellular context.
- Short-patch BER: Involves the removal of a single nucleotide.
- Long-patch BER: Can remove 2-10 nucleotides.
Here’s a simplified comparison of the two pathways:
| Feature | Short-Patch BER | Long-Patch BER |
|---|---|---|
| Number of nucleotides replaced | 1 | 2-10 |
| Primary polymerase | Polymerase beta | Polymerase delta or epsilon |
If you’d like to delve deeper into the specifics of the BER pathway, including the enzymes involved and the regulation of this important process, consider consulting reputable genetics or molecular biology textbooks or review articles. These sources provide a more comprehensive and technical explanation of BER.