cell communication

Signal transduction: hormones produced by endocrine cells are

secreted into the bloodstream & carried to the target cell

signal transduction: in paracrine signaling, molecules diffuse through the neighborhood of

the cell that secretes them, acting as local mediators; regulates inflammation & wound healing

signal transduction: neuronal signaling

electrical signals (action potentials) are converted to chemical signals (neurotransmitters) at a synapse

signal transduction: juxtacrine signaling

cells make direct contact through signaling molecules in their plasma membranes

acetylcholine: the neurotransmitter acts on skeletal muscle cells through an

ion channel-linked receptor

acetylcholine: in cardiac muscle cells it acts

through a G protein-linked receptor

activated a subunit of G protein switches on the adenylyl cyclase →

cAMP is synthesized from ATP, cAMP activates cAMP-dependent protein kinase a (PKA

the most frequent target enzyme for G proteins is adenylyl cyclase

activity of adenylyl cyclase alters intracellular concentration of cAMP

G proteins may also activate the membrane-bound enzyme phospholipase C; phospholipase C acts on an

inositol phospholipid, generating 2 messenger molecules which are IP3 & DAG

IP3 binds to (& opens ) CA++ channels in the ER; CA++ rushes out into the

cytoplasm; in muscle cells, it stimulates contraction

nuclear receptors serve as

transcription factors that regulate gene expression

nuclear receptors modulate gene expression through

through protein-DNA and protein-protein interactions

receptor tyrosine kinases

phosphorylate tyrosine residues in target proteins

tumor necrosis factor receptors

control inflammation and apoptosis