Editing DNA ligase (section)

== Enzymatic mechanism ==
[[File:Ligase.svg|thumb|The image demonstrates how ligase (yellow oval) catalyzes two DNA fragment strands. The ligase joins the two fragments of DNA to form a longer strand of DNA by "pasting" them together.]]
The mechanism of DNA ligase is to form two [[covalent]] [[phosphodiester bonds]] between [[3' end|3' hydroxyl ends]] of one [[nucleotide]] ("acceptor"), with the [[5' end|5' phosphate end]] of another ("donor"). Two ATP molecules are consumed for each phosphodiester bond formed. {{cn|date=January 2024}}AMP is required for the ligase reaction, which proceeds in four steps:

# Reorganization of activity site such as nicks in DNA segments or Okazaki fragments etc.
# Adenylylation (addition of AMP) of a [[lysine]] residue in the active center of the enzyme, [[pyrophosphate]] is released;
# Transfer of the AMP to the 5' phosphate of the so-called donor, formation of a pyrophosphate bond;
# Formation of a phosphodiester bond between the 5' phosphate of the donor and the 3' hydroxyl of the acceptor.<ref name="pmid4377758">{{cite journal | vauthors = Lehman IR | title = DNA ligase: structure, mechanism, and function | journal = Science | volume = 186 | issue = 4166 | pages = 790–7 | date = November 1974 | pmid = 4377758 | doi = 10.1126/science.186.4166.790 | bibcode = 1974Sci...186..790L | s2cid = 86549159 }}</ref>

[[Image:Ligation.svg|thumb|center|350px|A pictorial example of how a ligase works (with [[DNA end|sticky end]]s)]]

Ligase will also work with [[DNA end|blunt end]]s, although higher enzyme concentrations and different reaction conditions are required.