Second messenger

Second messenger system

The second messenger system is a method of cellular signal transduction. This process involves the transmission of a signal from the cell's exterior to its interior, causing a physiological response. The signal, or first messenger, binds to a receptor on the cell membrane, triggering the production of an intracellular molecule, or second messenger. The second messenger then initiates a series of intracellular events.

Overview

The second messenger model was proposed by Earl W. Sutherland Jr. in 1956. He discovered that adrenaline, a hormone, did not directly stimulate the conversion of glycogen to glucose. Instead, it initiated a complex series of reactions inside the cell. This discovery earned him the Nobel Prize in Physiology or Medicine in 1971.

Types of second messengers

There are several types of second messengers, including cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP), inositol trisphosphate (IP3), diacylglycerol (DAG), and calcium ions (Ca2+).

cAMP

cAMP is a derivative of adenosine triphosphate (ATP). It is synthesized by the enzyme adenylyl cyclase when the hormone epinephrine binds to a G protein-coupled receptor on the cell membrane.

cGMP

cGMP is a derivative of guanosine triphosphate (GTP). It is synthesized by the enzyme guanylyl cyclase when the hormone atrial natriuretic peptide binds to a receptor on the cell membrane.

IP3 and DAG

IP3 and DAG are derived from phosphatidylinositol 4,5-bisphosphate (PIP2). They are synthesized by the enzyme phospholipase C when the hormone vasopressin binds to a G protein-coupled receptor on the cell membrane.

Ca2+

Ca2+ is a universal second messenger. It is released from intracellular stores in response to a variety of signals, including IP3.

Function

Second messengers relay the signal from the cell membrane to the interior of the cell, where they initiate a series of intracellular events. These events may include changes in gene expression, cell growth, and cell death.

See also

• Signal transduction
• G protein-coupled receptor
• Adenylyl cyclase
• Guanylyl cyclase
• Phospholipase C

Second messenger Resources
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