Protein kinase C

Cyclic AMP

Cyclic GMP

Calcium

Diacylglycerol

The GPCR undergoes a conformational change, making a binding site available for a G-protein within the cytosol

The GPCR remains unchanged, as no covalent modifications have been made

The GPCR is released from the membrane and enters the intracellular space to trigger downstream signaling cascades

The GPCR become inactivated

The GPCR opens to permit an influx of sodium ions (Na+)

Second messengers give cells direct access to extracellular material by permeabilizing the membrane

Second messengers permit amplification of the signal

Second messengers permit fine-tuned modulation of the signal through various intracellular enzymes

Second messengers eliminate the need for molecules to cross the semi-permeable membrane

Second messengers can activate more than one pathway

Epinephrine (adrenaline)

cAMP

Ca2+

IP3

All of these are second messengers.

Secondary messengers are capable of crossing the phospholipid bilayer cell membrane, whereas primary messengers often are not.

Secondary messengers help primary messengers cross the phospholipid bilayer by making them hydrophilic or hydrophobic.

Secondary messengers can take up extra space in a cell, thus limiting the ability of other chemical reactions to interfere with cell processes.

Secondary messengers are able to bind to membranes, anchoring themselves in one place, whereas primary messengers float freely throughout the cell body and are unreliable.

None of these describe the unique role of secondary messengers.