Chapter 5: Signal Transduction Flashcards
Transduction
How cells communicate with each other
Receptors
Specific target-cell proteins that bind chemical messengers
Properties of most chemical messengers (2)
-water soluble
-bind at plasma membrane
Properties of steroids (2)
-lipid soluble
-bind to an intracellular receptor
Transmembrane protein
goes all the way through a membrane
Water soluble signal transduction
Induces a shape change on a portion of the protein
Water insoluble lipid transduction
Directly changes transcriptional profile of DNA
Antagonist
Anything that blocks a ligand from binding
Agonist
Binds to a receptor and enhances/mimics the receptor
Down-regulation
Decreases number of receptors if ligand is present
Up-regulation
Increase in number of receptors if ligand is lower in concentration
Specificity
Each cell responds to its own set of chemical messengers
Competition
Ability of different molecules to compete with a ligand for binding to its receptor
Speed of lipid soluble messengers
Slower but sustained
Speed of water soluble messenegers
Faster but less sustained
First messenger
Extracellular chemical messenger that binds to specific plasma membrane receptors
Examples of first messengers
Hormones, neurotransmitters
Second messengers
A substance generated in response to the first messenger
Examples of second messenegers
cyclic AMP, Ca2+
Where are second messengers generated?
Cytoplasm
Ligand-gated ion channels
Conformational change of receptor to open the channel
What opens a ligand-gated ion channel?
First messenger
Receptor tyrosine kinases
Have intrinsic enzyme activity that specifically phosphorylate tyrosine residues
What’s one thing all receptor kinases have in common?
All involve activation of cytoplasmic proteins by phosphorylation
What can the first messenger bound receptor turns on an enzyme to create guanylyl cyclase, what is the secondary product formed?
cyclicGMP
cGMP-dependent protein kinase
-Activated by cGMP
-phosphorylates other proteins
Where is the cGMP pathway found?
In the retina of the eye
Kinase
Receptor itself is an enzyme
Janus kinases (JAKs)
Receptor is just a receptor
What happens when the first messenger binds to the janus kinase?
Induces a conformational change
Where are JAK proteins used?
Immune reactions
What is an important molecule in protein binding to change conformation?
G protein
G protein is composed of three subunits. What are they and what are their functions?
alpha: binds to GDP
beta and gamma: anchor alpha subunit to membrane
Where is the G protein located?
Inside the membrane
What is Gs’ effector protein?
Adenylyl cyclase
What does adenylyl cyclase produce?
Cyclic AMP
What is the most important secondary messenger?
Cyclic AMP
What enzyme catalyzes the breakdown of cAMP into AMP?
cAMP phosphodiesterase
Increased cAMP in the cell means _______
Increased function
Inside the cell, what does cAMP bind to to create a cascade of cellular events?
cAMP-dependent protein kinase
True or false: all G proteins stimulate cAMP.
False; some are Gi, “inhibitory”
What is the main function of a G protein?
Controls ions channels
Direct regulation
G protein interacts with channel without second messengers
Indirect regulation
Second-messenger pathways used
What activated Gq?
Receptor bound to first messenger
Activated Gq activates plasma membrane effector enzyme _______
Phospholipase C (PLC)
Phospholipase C catalyzes the breakdown of what plasma membrane phospholipid?
PIP2
What is PIP2 broken down into by phospholipase C, and what is their function?
DAG and IP3, second messengers
DAG
activates another kinase by phosphorylating other proteins
IP3
binds to Ca2+ receptors on ER, increasing Ca2+ concentration in cytosol to help activate protein kinase C
What does the presence of Ca2+ create in the cell?
An electrochemical gradient
Where does the electrochemical gradient favour the higher concentration of Ca2+?
Into the cytosol
What is the second messenger associated with Ca2+?
IP3
IP3 regulates the release of Ca2+ from where?
ER
What protein undergoes a conformation change when activated, and can activate or inhibit other enzymes, when bound to Ca2+?
Calmodulin
What type are the Ca2+ channels in the plasma membrane?
Voltage-gated ion channels
When the first messenger subsides, what happens to the second messenger?
Intracellular concentration (of second messenger) decreases
