ligation

Ligation is the act of tying off a vessel or duct in a clinical or surgical context, and more broadly, the joining of two DNA fragments in molecular biology. In medicine, ligation is used to stop bleeding or to block the passage of substances through a duct or vessel. A common example is tubal ligation, a permanent contraception procedure that blocks the fallopian tubes to prevent fertilization. Ligation of the vas deferens is another approach used for male sterilization. Clinical ligation may be performed with sutures, clips, or electrocautery, and carries risks such as infection, bleeding, or incomplete occlusion (recanalization) in some cases.

In molecular biology, ligation refers to the enzymatic joining of DNA ends by DNA ligase. The enzyme forms phosphodiester bonds between a 5' phosphate and a 3' hydroxyl group, thereby sealing nicks or joining fragments. DNA ligases vary by origin and optimal conditions; T4 DNA ligase is commonly used in laboratory cloning. Ligation outcomes depend on end compatibility: cohesive (sticky) ends, blunt ends, and sometimes pre-processed ends. Applications include cloning genes into plasmids, constructing recombinant DNA molecules, and assembling multiple fragments for vector-based expression. Ligation efficiency is influenced by fragment concentration, end compatibility, temperature, and the presence of optimal cofactors.

Both senses of ligation emphasize the principle of creating a continuous channel or sequence through joining parts. In research, ligation is a foundational tool for genetic engineering; in medicine, ligation is a fundamental technique for controlling biological pathways and processes, with implications for contraception, pediatric and surgical care, and vascular management.