Cell and Molec Exam 4

signal transduction

the process of converting an extracellular signal into an intracellular signal to elicit a specific cellular response

long-range signals

endocrine

synaptic/neuronal

short-range signals

paracrine

contact-dependent

endocrine signaling

hormones are carried in the blood to distant target cells. public style of communication. broadcasts a signal (hormones) throughout the whole body through secretion into the bloodstream.

synaptic/neuronal signaling

transmitted along axons to remote target cells. in the case of neurons, however, the message is not broadcast widely, but is delivered quickly and specifically. when action potentials reach the axon terminal, electrical signals get converted into chemical signals in the form of neurotransmitters. the neurotransmitter then diffuses across the synaptic gap to reach the membrane of the target cell.

paracrine signaling

signals released by cells into extracellular fluid and act locally. signal molecules diffuse locally through the extracellular fluid. cells must be in the same vicinity. acts as a local mediator. signal molecules that regulate the inflammatory response work in this manner,

autocrine signaling

a type of paracrine signaling where the local mediators are produced by the cells themselves to promote their own survival or proliferation. cancer cells use this signaling to amplify their own activity

contact-dependent signaling

direct communication through cell to cell contact. cells make direct physical contact through signal molecules lodged in the plasma membrane of the signaling cell and receptor proteins embedded in the plasma membrane of the target cell. in embryonic development, contact-dependent signaling allows adjacent cells to become more specialized to form different cell types

are most extracellular signals large or small

large, so they require a membrane-bound receptor to pass the signal across the membrane and into the cell

effector proteins

initiate the targeted effect of the signal. acts on specific proteins or molecules to promote whatever the intended effect was

molecular switches

allow signals to switch between inactive and active states. easy and reversible ways to control signal transduction. once activated, these proteins can turn on other proteins in the signaling pathway. they persist in the active state until another switch turns them off

proteins that act as molecular switches

kinases

GTP-binding proteins

kinases

phosphorylate proteins. in the signal transduction pathway, phosphorylation of one protein can activate phosphorylation of the next, and so forth. kinases can target specific proteins. there are serine/threonine kinases and tyrosine kinases. these can add phosphate groups from either serine, threonine, or tyrosine residues, respectively.

GTP-binding proteins

their activation depends on whether or not GTP or GDP is bound

three classes of cell-surface receptors

ion channel coupled receptors

G-Protein-Coupled Receptors (GPCRs)

Enzyme-coupled receptors

ion channel coupled receptors

allows the flow of ions across a plasma membrane. results in changes in the membrane potential and produces an electrical current

G-protein-coupled receptors (GPCRs)

activates membrane-bound, trimeric GTP-binding proteins (G proteins), which then activate either an enzyme or an ion channel in the plasma membrane. each is composed off a single polypeptide chain that is a seven-pass transmembrane receptor protein. when bound to a signal molecule, the receptor protein undergoes a conformational change that enables it to activate a G protein on the underside of the plasma membrane. it has threre subunits, alpha, Beta, and gamma. in the unstimulated state, the alpha subunit has GDP bound, and the G protein is idle. when an extracellular ligand binds to the receptor, the receptor activates the G protein by causing the alpha subunit to release GDP, and exchange it for GTP. the alpha subunit has intrinsic GTPase activity, and ultimately, will hydrolyze the GTP back to GDP returning the G protein back to its inactive state. through prolonged stimulation, the receptor is worn out, so activation cannot continue.