Figure 1 : Errors in an error-correcting mechanism.

From: A unifying mechanism in neurodegeneration

Figure 1

Single-strand breaks in DNA can arise as a result of harmful molecules called reactive oxygen species (ROS). To repair these breaks, chains of poly-ADP ribose (PAR) molecules are synthesized by the enzyme PARP. This acts as a signal for scaffold proteins, including XRCC1, which move to the DNA and recruit repair enzymes. Hoch et al.2 report that mutations in the XRCC1 gene in humans cause defective DNA repair, leading to neuronal dysfunction and death, potentially by trapping complexes on DNA and hyperactivating PARP.