, second messengers
are low-weight diffusible molecules
that are used in signal transduction
to relay a signal within a cell
. They are synthesized or released by specific enzymatic
reactions, usually as a result of an external signal that was received by a
and pre-processed by other membrane-associated proteins
. There are two basic types of second messenger molecules:
These intracellular messengers have some properties in common:
- They can be synthesized/released and broken down again in specific reactions by enzymes.
- Some (like Ca2+) can be stored in special organelles and quickly released when needed.
- Their production/release and destruction can be localized, enabling the cell to limit space and time of signal activity.