Cell Signaling

signal transduction

Process by which one signal is converted to another. Signaling cells produce extracellular signal molecule that binds to receptors on target cells. Target cells converts signals to intracellular signaling molecules that alter cell behavior.

hormones, local mediators, neurotransmitters, membrane-bound signaling

4 extracellular signals

hormones

Secreted and transport via the blood stream to target tissues.

local mediators

diffused locally through extracellular fluid and act on nearby cells

neurotransmitters

neuron activated and sends electrical impulses down axon

membrane-bound signal

direct physical contact between cell-surface-bound signal molecule on signaling cell and receptor on target cell. 

Fast cell signaling

can take seconds to minutes and affects proteins that already exist in the cell

slow cell signaling

Can take hours to days. It must make changes in the gene expression and makes new proteins

intracellular receptors

Small hydrophobic signaling molecules can cross plasma membrane. Binds to nuclear receptors. 

Molecular switches

Intracellular signaling proteins that changes between active and inactive state in receiving a signal.

Switch 1

Proteins controlled by phosphorylation. Kinases adds phosphate group while phosphatase removes phosphate groups.

Switch 2

GTP-binding proteins. Inactive when GDP bound, active when GTP is bound.

Ion-channel

primarily found on nerve cells and muscle cells. Binds neurotransmitters and alters confirmation to open ion channel allows flow of ions - Na+,K+,Ca2+

G-protein

Largest family of receptors. Binds hormones, local mediators, and neurotransmitters. Seven-pass transmembrane proteins. Composed of alpha, and beta proteins.

Cyclic AMP signaling pathway 

Activator of cyclic AMP-dependent protein kinase (PKA)

Inositol phospholipid pathway

Another target of activated G-protien - phospholipase C

Enzyme-coupled receptors

Transmembrane protein - single pass

Receptor Tyrosine Kinases

Signal molecule binding triggers dimer formation. Activation of kinase domains - each tail phosphorylates the other.

Ras

Membrane-bound monomeric GTPase. Inactive Ras will exchange GDP for GTP upon interaction with Ras.

IP3

water-soluble, released into cytosol, binds and opens Ca ion channels in ER membrane

DAG

lipid, recruits and activates protein kinases C (PKC) in conjunction with Ca