**G alpha subunit**
**Definition**
The G alpha subunit is a component of heterotrimeric G proteins involved in intracellular signal transduction. It binds and hydrolyzes GTP to regulate various cellular responses.
**Article**
## Overview
The G alpha (Gα) subunit is one of three subunits (alpha, beta, and gamma) that compose heterotrimeric G proteins. These proteins act as molecular switches in transmitting signals from G protein-coupled receptors (GPCRs) on the cell surface to intracellular effectors.
## Structure and Function
The G alpha subunit binds guanine nucleotides—GDP in its inactive state and GTP when active. Upon activation by a GPCR, GDP is exchanged for GTP, causing the G alpha subunit to dissociate from the beta and gamma subunits. The activated G alpha subunit then interacts with downstream effectors such as adenylate cyclase or phospholipase C to modulate cellular activities.
## Classification
G alpha subunits are classified into several families based on their sequence and function, including Gαs, Gαi/o, Gαq/11, and Gα12/13. Each family regulates distinct signaling pathways and physiological processes.
## Role in Cellular Signaling
By controlling the activity of enzymes and ion channels, G alpha subunits play critical roles in processes such as hormone response, sensory perception, and neurotransmission. Their ability to hydrolyze GTP to GDP ensures timely termination of the signal.
**Meta Description**
The G alpha subunit is a key part of heterotrimeric G proteins that transduce signals from cell surface receptors to intracellular targets by binding and hydrolyzing GTP.