Cell Communication 1: Signal Transduction Flashcards
What is signal transduction?
extracellular signaling molecules bind to specific receptors in target cells to initiate a chain of events
Why is signal transduction important?
cell, tissues, and organs need to communicate in the development of the organism and for coordination of metabolism
What responses do external signals induce?
fast response
slow response
What is fast response?
change in activity or function of enzymes or proteins in the cell
What is slow response?
change in amounts of proteins by change in expression of genes
What is endocrine signaling?
long distance signaling
signal-bloodstream-distant target cells
freely diffusible signal
What is paracrine signaling?
acts locally
affects cells nearby and short lived signal
What is synaptic signaling?
acts locally
affects cell nearby
short lived signal
(neurotransmitters)
What is autocrine signaling?
cells resign to signals they themselves relates or release to cells of the same type
cells secrete signal that feeds back and binds to a receptor on its own surface
What is direct cell signaling?
ex) immune cells
Ag-presenting cells to T cells
What do cells do after receiving a signal?
survive
divide
differentiate
die
What are the three parts of a signaling module?
signals
receptors
effectors
What are signals?
(ligands)
Typically secreted by exocytosis
signals stay near or far
what are receptors?
bind specifically to signal molecules with high affinity (signals are produced in low levels)
What are effectors?
targets of receptors inside cells: alter activity of many different proteins and generate 2nd messengers (small diffusible molecules like cAMP and Ca2+)
What are the main categories of ligands?
small lipophilic molecules: steroid hormones
water soluble molecules - hydrophilic- e.g. growth factors
Receptors can bind to ligands with _____ affinity, which means ____
high; great specificity to the ligand (conc of ligand is low in bloodstream)
What are the two types of receptors?
cell surface receptors
intracellular receptors
What are cell surface receptors?
external domain binds ligand, transmembrane domain anchors receptor, cytoplasmic domain initiates signal by change in conformation
What are intracellular receptors?
steroid receptor can have receptor in cytosol- alters gene expression in nucleus
Most signaling molecules are hydrophilic and require ______
cell surface receptors
One major class of surface receptors that mediate transduce a binding event on the cell surface to send signal inside the cell
G protein coupled receptors
What is a G protein coupled receptors?
receptor composed of 3 parts:
extracellular domain
transmembrane domain
cytoplasmic domain
What does the extracellular domain do?
binds to ligand
What does the transmembrane domain do?
anchors receptor
What does the cytoplasmic domain do?
associates with G protein
What are the three protein subunits of G proteins
alpha, beta, gamma
What are the 3 components of G protein coupled receptor pathways?
inactive receptor
receptor G protein
inactive effector
G protein coupled receptors are characterized by _______
seven membrane spanning alpha helices
What type of proteins are G proteins? what do they assist in?
guanine nucleotide binding proteins
assit in transmitting signals to intracellular targets
What is an example of an effector?
downstream adenylyl cyclase that generate cAMP
What are the steps of G-protein relaying signals?
- ligand binds to receptor
- conformational change occurs in receptor
- receptor binds to G protein
- receptors acts as guanidine exchange factor
- confirmation of G alpha protein is changed to kick out GDP for GTP
- G alpha becomes active and binds effector molecule to activate it
- effector molecule can catalyze formation of cAMP
What is the target in the cholera toxin?
G protein
What does cholera do to G protein?
modifies it by keeping the G alpha in the GTP active form indefinitely, pathway is always active causing Cl- and water to pump out of cells in intestines to cause severe diarrhea
G alpha s stimulates ________
adenyly cyclase
G alpha I inhibits _______
adenyly cyclase
cAMP interacts with target proteins to cause a _______ and activates a protein kinase called ______
biological response; PKA
What does a kinase do?
phosphorylates proteins to either activate or inactivate them
________ induces activation of PKA
epinephrine
What does the downstream do?
generate lots of ATP for a response to threat
in liver: glycogen breakdown to glucose, inhibition of glycogen synthesis
cardiac muscles: increase contraction rate
adipose tissue: hydrolysis of triglycerides to generate more glucose
What is desensitization?
ability to turn off or reject the signal
What ways can desensitization occur?
receptor sequestration
receptor destruction
hormone level drop
remove the signaling molecule
What is receptor sequestration?
endoscope- invagination of membrane
What is receptor destruction?
endoscopes and lysosomes
What is hormone level drop?
decreased adenyly cyclase activity to decreased cAMP and decreased PKA activity
What is removing the signal molecule?
phosphodiesterase will remove cAMP
What do G protein receptor kinases do?
phosphorylate the receptor such that another protein called arresting will bind to the 3rd intracellular loop of receptor and prevent G alpha from interacting with third loop of the receptor
What does GRK result in?
G protein G alpha-GDP does not get converted to G alpha-GTP by receptor
