You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Dynamics of site switching in DNA polymerase. DNA polymerases replicate DNA by catalyzing the template-directed polymerization of deoxynucleoside triphosphate (dNTP) substrates onto the 3' end of a growing DNA primer strand. Many DNA polymerases also possess a separate 3'-5' exonuclease activity that is used to remove misincorporated nucleotides from the nascent DNA (proofreading). The polymerase (pol) and exonuclease (exo) activities are spatially separated in different enzyme domains, indicating that a mechanism must exist to transfer the growing primer terminus from one site to the other. Here we report a single-molecule Förster resonance energy transfer (smFRET) system that directly monitors the movement of a DNA substrate between the pol and exo sites of DNA polymerase I Klenow fragment (KF). FRET trajectories recorded during the encounter between single polymerase and DNA molecules reveal that DNA can channel between the pol and exo sites in both directions while remaining closely associated with the enzyme (intramolecular transfer). In addition, it is evident from the trajectories that DNA can also dissociate from one site and subsequently rebind at the other (intermolecular transfer). Rate constants for each pathway have been determined by dwell-time analysis, revealing that intramolecular transfer is the faster of the two pathways. Unexpectedly, a mispaired primer terminus accesses the exo site more frequently when dNTP substrates are also present in solution, which is expected to enhance proofreading. Together, these results explain how the separate pol and exo activities of KF are physically coordinated to achieve efficient proofreading.
{"Chemical": ["nucleotides", "deoxynucleoside triphosphate", "dNTP"]}