2 - GATED ION CHANNELS AND TRIMETRIC G PROTEINS

What are gated ion channels as transduction systems?

Membrane proteins that open or close in response to specific stimuli (ligands, voltage, signals, or mechanical stress), allowing selective ion flow that alters membrane potential and triggers cellular responses.

Structure of Nicotinic acetylcholine receptors

Heteropentamer composed of two alpha subunits and one each of beta, gamma, and delta, each containing four transmembrane helices

Function of Nicotinic acetylcholine receptors (Ligand-gated channel)

ACh binds cooperatively to the alpha subunits, causing a conformational change that opens the channel and allows Na+ and Ca2+ to flow into the cell

Signal-gated channels

Open in response to intracellular signals such as cAMP. Linking second messenger pathways to ion flow and cellular responses.

Voltage-gated channels

Open in response to changes in membrane potential. Crucial for action potentials and signal conduction in neurons and muscles.

Mechanosensitive channels

Respond to mechanical deformation of the membrane. Playing roles in touch, hearing, and osmoregulation by translating physical forces into electrical or chemical signals.

Trimetric G proteins structure

Alpha, beta, and gamma subunits. The alpha subunit binds to GDP/GTP and possesses GTPase activity. Beta and gamma stay together where alpha can separate when active.

Trimetric G proteins interaction with membrane and receptors

The beta-gamma complex anchors the protein to the membrane and assists in receptor interaction

Trimetric G proteins receptor

Spans the membrane 7 times and binds a signal. Changes the receptor’s shape and activates the G protein by swapping GDP for GTP on the alpha subunit

Trimetric G proteins subunit as an enzyme

When it has GTP, it can turn on other proteins like enzymes. It slowly breaks GTP into GDP to shut itself off again.

Trimetric G proteins Guanosine nucleotide exchange factors (GEFs)

Help remove GDP and add GTP on the alpha subunit, turning the G protein on faster

Trimetric G proteins GTPase Activator Proteins (GAPs)

Accelerate the hydrolysis of GTP to GDP on the alpha subunit, turning the G protein off sooner

Trimetric G proteins Alpha subunit enzyme

Intrinsic GTPase activity to hydrolyze GTP, inactivating itself