the idea that, especially in terms of microbiology, molecules will fit a receptor site exactly, similar to how a certain fits a certain lock only. Other theories include the induced fit model.

LOCK-AND-KEY THEORY: "The lock and key theory states for every substrate that is an exact active site which is complementary."
Cite this page: N., Pam M.S., "LOCK-AND-KEY THEORY," in PsychologyDictionary.org, April 7, 2013, https://psychologydictionary.org/lock-and-key-theory/ (accessed November 13, 2020).