Day 1 Cell Communication

signal molecule/ligand

molecule that binds to a receptor, triggering a response; can be lipid soluble or water soluble

lipid soluble signal molecules

small or hydrophobic ligands (ex. steroid and thyroid hormones) that can cross the plasma membrane directly and bind intracellular receptors

water soluble signal molecules

ligands (ex. peptide hormones, epinephrine) that can’t cross the membrane and instead bind receptors on the cell surface

receptors

intracellular and membrane

intracellular receptors

sit in the cytoplasm/nucleus and bind lipid-soluble signals; membrane receptors (GPCRs, RTKs, ion channels) sit in the plasma membrane and bind water-soluble signals

second messengers (cAMP)

small, nonprotein, water soluble molecules or ions (cyclic AMP, Ca2+) that rapidly diffuse through the cell, spreading and amplifying a signal

adenylyl cyclase

enzyme in the plasma membrane that converts ATP into cyclic AMP (cAMP) in response to an activated G protein

reception

first stage of cell signaling: detection of a signal molecule by a receptor, from outside or inside the cell

signal transduction

second stage of cell signaling: converting a received signal into a form that causes a specific cellular response, usually through a series of relay molecules that change shape.

phosphorylation cascade

chain of protein kinases that activate each other in sequence by transferring phosphate groups, amplifying and relaying a signal.

kinases and phosphatases

Kinases transfer a phosphate group from ATP to a protein (generally activating it); phosphatases remove a phosphate group from a protein (generally inactivating it), releasing inorganic phosphate.

gene expression

common endpoint of signal transduction pathways, where an activated transcription factor turns specific genes on or off.

signal amplification

The exponential increase in the number of activated molecules at each step of a signaling pathway, so that a single signal molecule can produce a massive cellular response