Ch 16 Textbook Material Pt2 (general principles of cell signaling)

What is the role of GEFs (guanine nucleotide exchange factors)?

activate GTPases by promoting exchange of GDP for GTP

What is the role of GAPs (GTPase-activating proteins)?

inactivate GTPases by promoting GTP hydrolysis to GDP

How do GTP-binding proteins act as timing mechanisms?

their intrinsic GTPase activity ensures they automatically turn off after a set period

What do all cell-surface receptor proteins do?

they bind to an extracellular signal molecule and transduce its message into intracellular signaling molecules that alter the cells behavior

What are the three main classes of cell-surface receptors?

• ion-channel-coupled receptors

• G-protein-coupled receptors (GPCRs)

• enzyme-coupled receptors

How do ion-channel-coupled receptors work?

they change the plasma membranes permeability to specific ions, altering the membrane potential and possibly producing an electrical current

How do G-protein-coupled receptors (GPCRs) work?

they activate trimeric GTP-binding proteins (G proteins), when then activate or inhibit enzymes or ion channels

• triggering an intracellular signaling cascade

How do enzyme-coupled receptors work?

they either act as enzymes themselves or associate with intracellular enzymes that activate signaling pathways when the receptor is stimulated

What is another name for ion-channel-coupled receptors?

transmitter-gated ion channels

Where are ion-channel-coupled receptors especially important?

in nerve cells and other electrically excitable cells such as muscle cells

What type of signaling do ion-channel-coupled receptors mediate?

rapid transmission of signals across synapses in the nervous system

What happens when a neurotransmitter binds to an ion-channel-coupled receptor?

the receptor changes conformation and opens an ion channel, allowing specific ions (Na+, K+, or Ca2+) to move across the membrane