CH 5 - Signal Transduction Flashcards
(22 cards)
receptor
proteins or glycoproteins located either in the cells plasma membrane or inside the cell, either in the cytosol or nucleus
Signal transduction steps
- messenger binds to receptor and changes the conformation of the receptor and activates it
- signal activates the receptor and the stimulus is transformed into a response
Antagonist
blocks the action of a chemical messenger
Agonists
mimic the messenger’s action
What does the percent saturation of a binding site depend on?
The concentration of unbound ligand in solution and affinity of the binding site for the ligand
What is a characteristic that all first messengers share?
They are extracellular
What is a characteristic that all second messengers share?
They are intracellular and respond when a first messenger binds to a receptor on the membrane
What’s more important: Ligand or receptor?
The receptor is more important
What are the two things an effector protein will do?
Forms CAMP and degrades GTP to GDP
transmembrane protein
- water soluble
- first messengers bind to plasma membrane receptors
- second messengers diffuse throughout the cell
- protein kinase phosphorylates other proteins by transferring a phosphate group from ATP
intracellular receptors
- lipid soluble
- in cytosol or cell nucleus
- transduce signals through interactions with genes
- messenger diffuses out of capillaries from plasma to the interstitial fluid
- messenger diffuses across the lipid bilayers of the plasma membrane to enter the nucleus
- activated receptor complex acts as a transcription factor
- hormone receptor complex binds of DNA at the regulatory region and increases the rate of transcription into mRNA
lipid soluble messengers
- diffuse through plasma membrane
- have intracellular responses
- signal receptor complex binds directly to recognized sequences in the DNA and alter gene transcription
- slower response activation but sustained response
water soluble messengers
- activate intracellular signaling cascades that affect cell function
- can activate downstream mediators, which affect DNA transcription
- faster response activation but less sustained response
receptors that are ligand gated channels
- ligand binds to receptor (water soluble membrane receptor)
- receptor can change conformation and change affinity for ligand
- net diffusion of ions across plasma membrane
- cell response
receptors that function as enzymes
- The binding of a specific messenger to the receptor changes the conformation of the receptor so that its enzymatic portion, located on the cytoplasmic side of the plasma membrane is activated
- The receptor phosphorylates some of its own tyrosine residues
- phosphotyrosines on the cytoplasmic portion of the receptor serve as docking sites for cytoplasmic proteins
- bound docking sites then bind and activate other proteins, which activate on or more signaling pathways within the cell
tyrosine kinase
enzyme inside the receptor
receptors that interact with cytoplasmic janus kinases
- janus kinase is a class of enzymes associated with a receptor
- synthesis of new proteins that mediate the cells response to the first messenger
G protein coupled receptors
- ligand binds to receptor as first messenger
- GDP gets converted into GTP and GTP breaks off with the alpha subunit because there is a change in affinity for EP
- EP forms CAMP and degrades GTP to GDP
alpha subunit with GDP
high affinity for receptor
alpha subunit with GTP
high affinity for effector protein
cyclic AMP
second messenger inside the cell, made by alpha subunit
formation and breakdown of CAMP
- ATP –> CAMP by the action of the plasma membrane enzyme adenylyl cyclase
- CAMP is inactivated by systolic enzyme CAMP phosphodiesterase
- CAMP phosphodiesterase converts CAMP –> AMP
