CELL SIGNALING Flashcards
why do cells communicate?
allows coordination of tasks and ensures one cell isn’t doing all of the work needed for proper functions
where do cellular signals come from?
signals can come from the environment, from other cells, from mechanical stimulus, or direct cell contact
what are signaling networks and what role do they play?
they receive, transmit, and process information, allowing for the initiation of cellular responses
what is cell-cell signaling?
a cell has the signal and another cell has a receptor - they must come in contact for signaling
what is endocrine signaling?
signal is released into bloodstream and can be transmitted to a distant cell/target
what is paracrine signaling?
one cell will release a signal into the environment and a nearby cell is affected
what is autocrine signaling?
cell releasing the signal is also the cell receiving it
what are cell-impermeant molecules?
molecules that don’t easily pass through the cell membrane and must interact with receptors
what are cell-permeant molecules?
small molecules that can readily cross the cell membrane
what are cell-associated molecules?
molecules attached to membrane surface and directly interact with receptors on neighboring cells
what role do neurotransmitters play?
endocrine or paracrine signaling; neurohormones act via bloodstream on target cells and bypass nontargets, neurotransmitters directly act on targets
what role do peptide hormones play?
mainly endocrine signaling; cell-impermeant so they activate surface receptors - one growth factor to note is PDGF, it acts in blood clotting
what role does nitric oxide play?
paracrine signaling molecule; can diffuse through membranes and activate guanylyl cyclase to produce cGMP - PDE5 is enzyme responsible for this conversion
what role do nuclear receptor superfamilies play?
endocrine signaling molecules; will bind to receptor that’s held by chaperone and act as transcription factors
what role do eicosanoids play?
lipid-based signaling molecules; arachidonic acid as precursor; prostaglandins; different cells can respond differently to same ligand
how do membrane diffusable signaling molecules transduce a signal to the nucleus?
via signaling pathways; can be endocrine or paracrine paths
how do GPCRs transduce a signal from the outside to the inside of the cell?
7-pass-transmembrane receptor; extracellular domain binds to ligand and intracellular domain has guanine nucelotide exchange factors (GEFs); binding will cause conformational change and G-protein activity
how is the G-protein converted from an inactive to active state?
if alpha subunit binds to GDP, it will associate with beta and gamma subunits, creating the inactive form
if it binds to GTP, then it will dissociate from the other 2 subunits and be in an active form
GTP hydrolysis will create GDP - turning off protein
what are GEFs and GAPs?
GEFs - guanine nucleotide exchange factors; turn on signaling by catalyzing exchange of GDP for GTP
GAPs - GTPase activating proteins; terminate signaling by inducing GTP hydrolysis
what is cAMP and how is it made?
cyclic adenosine monophosphate; secondary signaling molecule; synthesized from ATP by adenylyl cyclase
what is signal amplification?
increase in intensity of a signal through networks of intracellular reactions
how is it possible for the same signal to have different effects on different cells?
different cell types have different receptors + intracellular pathways, so responses can vary based on what receptor is triggered
what is the function of protein kinases and phosphates?
act as molecular switches by adding/removing phosphates, which activates and regulates protein activity
kinases turn on a protein by adding a phosphate
phosphatases turn off protein by removing
how do receptor tyrosine kinases (RTKs) transduce a signal from outside to inside a cell?
they bind to a specific extracellular ligand which will trigger dimerization of the receptor; tyrosine kinase will become active via cross phosphorylation and through a series of reactions it will send a signal to the nucleus
what are non-receptor tyrosine kinases?
NRTKs are intracellular and modulate intracellular signaling; receptor are cross phosphorylated and phosphorylated
what are SH2 domains and what role do they play?
protein module found in tyrosine kinase signaling pathways; they bind tyrosine-phosphorylated sequences in specific targets
what is crosstalk?
occurs when a signal is shared between multiple pathways; components of one pathway may impact another
what is Ras and how can it be activated/inactivated?
a small GTP binding protein that’s part of a growth factor signal transduction pathway; GEFs inactivate/activate it - GDP bound will be inactive and GTP will be active
how are scaffold proteins useful?
they act as hubs for multiple proteins to organize efficient functional units in cascades
how do PI3 kinase and OLC interact with PIP2?
PI3K will create PIP3 from PIP2 - activates Akt pathway
OLC will create IP3 and DAG from PIP2 - to trigger Ca release and activate PKC
what is ubiquitin?
protein that is attached to molecules that need to be degraded
how does ubiquitination of IkB in response to cell signaling influence the activity of the transcription factor NF-kB?
ubiquitination of IkB will cause it to degrade, which will signal for the activation of NF-kB, allowing it to translocate to the nucleus and initiate transcription
what type of regulation does the NF-kB pathway have?
negative feedback loop; NF-kB is inhibited by IkB but also induces transcription of IkB, so regulates itself
how does proteolysis differ between NF-kB pathway and Notch signaling?
in NF-kB proteolysis occurs to the inhibitory protein but in Notch it happens directly to the receptor
