exam 2 cellular communication Flashcards
how do cells communicate with each other
receptors, which bind to signal molecule ligands
what is the outcome of signaling
rapid changes in protein function snd/or slower changes in gene expression
how do hydrophobic ligands cross membranes
easily to activate intracellular receptors
how do hydrophilic ligands cross membranes
they bind to cell-surface transmembrane receptors
what does signal transduction from cell-surface receptors require
the activation or generation of second messengers, which transmit the signals from the cell surface to the effectors
what are the three basic modes of signaling
- ion channels
- enzyme-coupled receptors
- G-protein-coupled receptors
what are the three steps of signaling
reception, transduction, response
what signaling can secreted molecules do
paracrine, endocrine, and synaptic siganling
what is paracrine signaling
act as local mediators, affecting only cells in the immediate environment of the signaling cell
what is endocrine signaling
travel long distances through the bloodstream to act on distant targets
what is synaptic signaling
travel via axons
what is autocrine signaling
a cell secretes signal molecules that can bind back to its own receptors
when is autocrine signaling useful
in positive or negative feedback loops - allow cells to amplify the signal or make one that is self-limited
what is contact-dependent siganling
signal molecules remain bound to the surface of the signaling cell and influence only cells that contact it
what can signaling molecules do/alter
slowly or rapidly alter the function of a target cell or flip the protein on or off or change the amount of protein to alter protein function
can signals work together
yes and cells can be programmed to respond to one combination of signals by growth/division, and these can promote survival
what happens when cells are deprived of their signals
they activate apoptosis
how do cellular responses vary
according to the receptor proteins the cell has and the intracellular signaling machinery the cell uses to interpret them
what are morphogens
molecules that diffuse out from signaling centers in developing tissues, creating a morphogen concentration gradient
how do cells adopt different fates from each other
depending on their position in the gradient. in this way layers of cells develop, each with a different function based on their concentration
how can concentration amount be useful
can determine where molecules are in the cell based on it
what are the types of signals
mechanical, light, heat, chemical
what forms do chemical stimuli come in
amino acids, small peptides, proteins, nucleotides, steroids, fatty acid derivatives, dissolved gasses
what does exocytosis do
signal molecules are secreted from the signaling cell into the extracellular space
how are some cells exposed to extracellular space
- exposed to the extracellular space while remaining tightly bound to the signaling cell’s surface
- released by diffusion through the plasma membrane
what happens with lipid soluble signaling molecules
they can simply diffuse across the plasma membrane
what signal molecules are lipid soluble
steroid hormones and gaseous signaling molecules
what happens with steroid hormones
they travel to their target cells via carrier proteins and bind to intracellular receptors, which can either be cytosolic or nuclear
what family are receptors for steroid hormones a part of
the nuclear receptor subfamily
prior to ligand binding, what do receptors bind to
an inhibitory protein and are inactive
what does ligand binding cause
a conformational change in the receptor, which causes an inhibitory protein to dissociate
what does a conformational change expose
exposes a site which binds to the promoter region upstream of a specific targeted gene
what occurs with transcription of a targeted gene
it’s then increased, producing specific proteins leading to changes in cell behavior
what happens to hydrophilic/lipid insoluble signals
they cannot cross cell membranes and they must bind to sites on cell surface receptors
what are ligand-gated ion channels
binding of ligands to the channel causes it to open and allows specific ions to flow through
what are enzyme coupled receptors
activate an enzyme when activated by a signal molecule binding to a receptor
what are G-protein-coupled receptors
activation of receptor causes a change in GTP vs GDP binding of a switch protein, which turns downstream enzymes on or off
what are ion-channel-coupled receptors involved in
synaptic signaling - opened/closed by neurotransmitters
what do ion-channel-coupled receptors do
alter ion permeability to cause membrane potential changes
what family are G-protein-coupled receptors from
large family of multi-pass transmembrane proteins
what do G-protein-coupled receptors indirectly regulate
the activity of a nearby target protein in the membrane
what do G-protein-coupled receptors contain
a GTP binding protein complex that acts as the middle man between an activated receptor and its target
what do enzyme-coupled receptors function as
protein kinases
what do enzyme-coupled receptors indirectly regulate
the activity of a nearby target protein that is in kinase cascade
what does the kinase cascade allow for
rapid amplification of signals
what carriers a first messenger signal across the plasma membrane
cell-surface receptors
what do second messengers do
they are a combination of activated enzymes and small intracellular molecules that amplify the signal and spread it through the cell
what regulates a cell’s responses
activated effector proteins
what are molecular switches activated by
- kinases/phophatases: phosphorylation/dephosphorylation
- GTPases/GTP-binding proteins
what forms protein complexes called signaling complexes
enzymes activated by a receptor protein
what do signaling complexes regulate
speed, efficiency, specificity of a cellular response
how can signaling complexes be organized
organized around a scaffold protein, assembled following receptor activation or on phosphorylated lipids
what do enzyme-coupled receptors interact with
receptor tyrosine kinases, which dimerize and phosphorylate themselves upon ligand binding
what do receptor tyrosine kinases allow for
recruitment of other ligands to bind and increases substrate range of kinase to phosphorylate other targets
what activates the GTPase signaling protein, Ras
tyrosine kinase, which covalently attaches to lipid anchor (inner leaflet of plasma membrane)
what does Ras initiate
a cascade of phosphorylation events mediated by a group of MAP kinases
when bound to a ligand, what does a G-protein-coupled receptor do
releases GDP and binds to GTP
when not bound to a ligand, what does a G-protein-coupled receptor do
it’s bound to GDP
what is cAMP
a common second messenger
