Cell Signaling

What is communication between cells mediated by

Extracellular signal molecules

Reception of signals depends on what

receptor proteins on cell surface or within cell or no cell nuclear membrane

what is activated when signal binds

receptor, then signal pathway

what happens after signal pathway is activated

intracellular signaling proteins process signals, then effector proteins target changes in cell behavior

effector proteins

gene regulatory proteins, enzymes, ion channel proteins, parts of a metabolic pathway, or cytoskeletal proteins

what are the extracellular signals

can be many things

proteins

amino acids

steroids

are extracellular signals membrane bound

can be or are released into extracellular space by exocytosis or diffusion into extracellular space

what do extracellular signals bind

specific reeptors on cell surface (transmembrane proteins) or other places in a cell

contact dependent signaling

signal remains attached to cell surface receptor of the signaling cell and influences only those cells it contacts

when is contact dependent signaling important

during development and immune response

paracrine signaling

signals (local mediators) are released but affect only targets in the vicinity

autocrine signals

cells produce signals that they respond to themselves

example of autocrine cells

cancer cells

synaptic long-range signalers

nervous system neurons with long axons that release chemical neurotransmitters onto post-synaptic sites

post-synaptic sites

synapse in the locale of release

endocrine long-range signaler

hor,onal system cells synthesize and release chemical hormones into bloodstream to affect distant targets

four types of signaling

contact-dependent

paracrine

synaptic

endocrine

signal integration

cells must integrate and respond to multiple signals to provide the appropiate reaction at the appropiate time

what happens if there is no receptor

no signal, cell death

what is different cellular response

different cell types respond to the same signal differently

what is the cell response to a signal dependent on

internal signals, effectors, and genes

ion-channel-couples cell-surface receptors

rapid signals mediated by neurotransmitters that open or close ion channels based on excitation or inhibition of the post0synaptic target; ion channel is coupled to a transmembrane protein

GPCR

signal activates receptor and GTP-binding protein, activates target

what can the targets of GPCR be

enzymes, other proteins, ion channels

how do the G-protein subunits attach to the cytosolic lipid bilayer

with an anchor

enzyme-coupled receptors

can act as enzymes themselved once activated or associate and activate with enzymes intracellularly

what happens once a cell membrane receptor has bound an extracellular signal

a second messenger is sent within the cell

examples of second messenger signals

cAMP, calcium, diacylglycerol

what do second messengers do

pass along signal to effectors

what are effectors

molecular switches with on and off properties

what are intracellular responses examples

GTP binding, phosphorylation via kinases, removal of phosphate by phosphatases, altered protein conformation

what must intracellular responses be

reversible or an over-action will occur

signaling by phosphorylation pathway will

be turned on with phosphate

turned off without phosphate

signaling by GTP binding will be

turned on with GTP

turned off without GTP

fast response toe extracellular signal

if changes occur to proteins already present within the cell; altered protein function

slow response to extracellular signal

if changes to gene expression or new protein synthesis are required; altered protein synthesis

largest family of cell-surface receptors

GPCR

what is the similar structure of GPCR

polypeptide with several transmembrane domains and use of G proteins to signal cell interior

G proteins

trimeric GTP-binding proteins attached to cytoplasmic face of cell membrane

what does the G-protein do

couples the receptor to either enzymes of ion channels

what happens when signal binds to GPCR

receptor activates the G protein

G protein structure

3 subunits (alpha, beta and gamma)

what does the subunit alpha of a G protein do

a GTPase binds GDP and keeps G protein inactive but then releases GDP and binds GTP which activates G protein

what does the G protein bind when activated

targets that include enzymes or ion channels

are G proteins stiulatory or inhibitory

depends based on the activation or inhibition of adenylyl

what does adenylyl cyclase do

increases or decreases cAMP

what kind of molecules move directly across the cell membrane

hydrophobic signal molecules, steroid, fat soluble, thyroid

what is the superfamily

signals that bind to intracellular receptor proteins which then control transcription

two ways to respond to hormones

primary and secondary

primary response to steroid hormone

directly activate primary-response genes

secondary response to steorid hormone

primary response protein turns on secondary response genes

diseases if the signal is lost

diabetes type I

loss of immune protection

diseases if cell signal does not reach target

multiple sclerosis

disease if target cell does not respond

diabetes type 2

disease if too much signal

stroke with release of glutamate in brain