biol 1406 chapter 9

cell communication

the process by which cells detect and respond to signals in their environment

two components required for cell signaling

ligand (signaling molecule) and a receptor protein (molecule that binds to the signal)

what happens when a ligand binds to its receptor

forms a receptor-ligand complex that initiates signal transduction which converts the signal into a cellular response

what determines which signals a cell responds to

the number and type of receptors on its surface

four types of cell signaling

direct contact, paracrine signaling, endocrine signaling, and synaptic signaling

direct contact signaling

cells communicate through surface molecules that touch, often during early development

paracrine signaling

short-range communication where cells release local signals affecting nearby cells

endocrine signaling

long-distance signaling where hormones travel through the bloodstream to target cells

synaptic signaling

communication between nerve cells using neurotransmitters across a chemical synapse

two main type of receptors

intracellular receptors and cell-surface (membrane) receptors

three subclasses of membrane receptors

channel-linked receptors, enzymatic receptors, G-protein-coupled receptors (GPCRs)

channel-linked receptors

chemically gated ion channels that open to allow specific ions through a pore when a ligand binds, example is neurons

enzymatic receptors

receptors that act as enzymes, often protein kinase that add phosphate groups (phosphorylation)

G-protein-coupled receptors (GPCRs)

receptors that activate G proteins, which then regulate enzymes or ion channels and can generate second messengers like cAMP, examples are peptide hormones and rod cells in the eyes

what types of signals bind to intracellular receptors

small or lipid-soluble molecules that can cross the cell membrane (steroid hormones)

steroid hormone receptor location before and after binding

before: cytoplasm
after: nucleus

primary function of steroid hormone receptors

regulators of gene expression

three domains of a steroid receptor

hormone-binding domain, DNA-binding domain, and coactivator-interaction domain (controls transcription level)

function of receptor kinases

regulate cell processes like cell cycle, migration, metabolism, and proliferation

how are receptor kinases activated

autophosphorylation (the receptor phosphorylates itself when a ligand binds)

what happens after receptor kinases activation

triggers a cascade of phosphorylation events, leading to a cellular response

function of GPCRs

transmit signals from outside the cell to inside by activating G proteins

what are G proteins made of

three subunits (alpha, beta, and gamma) that bind either to GDP or GTP

when are G proteins active or inactive

active when bound to GTP, inactive when bound to GDP

what happens when a ligand binds to a GPCR

GPCR activates a G protein → stimulates an effector (enzyme or ion channel) → produces second messengers (like cAMP) to amplify the signal

processes that involve GPCRs

hormone responses, neurotransmission, immune responses, and sensory perception