A series of steps by which the signal on a cell's surface is converted into a specific cellular response 

Convert signals into cellular responses 

Pathway similarities suggest thta ancestral signaling molecules evolved in prokaryotes and were modified later in eukaryotes 

Concentration of signaling molecules allows bacteria to detect population density 

Ex: Fruiting buds in bacteria 

Messenger molecules that travel only short distances 

Often used in animal cells for communication 

Reception 

Transduction

Response 

The molecule that binds to the receptor when a signal is sent

Highly specific to receptor 

A shape change in a receptor is often the initial transduction of the signal 

Most signal receptors are plasma membrane proteins 

A plasma membrane receptor that works with the help of a G Protein

 A family of proteins involved in transmitting chemical signals originating from outside a cell into the inside of the cell

Act as an on/off switch

If GDP is bound to the G protein, the G protein is inactive 

Membrane receptors that attach phosphates to tryosines 

Can trigger multiple signal transduction pathways at once [image]

Ligand-Gated Ion Channel

A receptor that acts as a gate when the receptor changes shape 

When a signal moleule binds as a ligand to the receptor, the gate allows specific ions, such as Na+ and Ca2 through a channel in the receptor [image]

Chemical messengers that can readily cross the membrane and activate the intended receptor 

Ex: Steroid and thyroid hormones of animals