Exam 2 Lecture 15 Flashcards
In G protein activation, the 𝛼 subunit acts like what?
It acts like Pac-man to allow GDP to exchange to GTP
What are the 4 major steps in G protein activation?
- Agonist binding
- G protein coupling & nucleotide exchange
- Activated G protein subunits regulate effector proteins
- GTP hydrolysis and inactivation of G𝛼 protein
What is the major role of adenylate cyclase?
Converts ATP to cAMP
What are some examples of ligands and receptors in the Gq pathway?
Ligands: acetylcholine and Ang II
Receptors: muscarinic acetylcholine receptors and Angiotensin II receptors
What is a central enzyme in the Gq pathway?
Phospholipase C
What is the G𝛼q effector?
Phospholipase C𝛽 (PLC𝛽) that triggers an increase in cytosolic Ca2+
What does PLC𝛽 do?
It hydrolyzes PIP2 to DAG and IP3
What is the role of IP3?
It is a second messenger that gates calcium release through Ca2+ channel from the ER
How does calcium binding to cytosolic proteins alter their function?
Example is protein kinase C (PKC) in which cytoplasmic PKC is inactive but Ca2+ binding promotes PKC binding membranes where its activator DAG is located
What is the difference in the free calcium levels inside and outside the cell?
Inside the cell is 10^-7 M and the outside of the cell is 10^-3 M (the ratio is 10^4)
How do small increases in the free calcium level (to 10^-6 M) activate certain cellular functions?
An example of this is the release of Ca2+ from the ER as a result of Gq activation
What are the 3 routes to remove Ca2+ from the cell?
- NCX: sodium calcium exchanger → moves Ca2+ out of the cell (Na+ driven)
- Ca2+ ATPase → pumps Ca2+ out
- SERCA: sarco/endoplasmic reticulum Ca2+ ATPase → pump Ca2+ out of the cell or back to the ER
The 3 routes to remove Ca2+ from the cell are all examples of what type of transport?
Active transport to maintain low levels of free calcium in the cytosol
What does the Ca2+ ATPase and SERCA have in common?
They both utilize ATP to remove Ca2+ from the cell
What is calmodulin?
It is a calcium dependent enzyme that binds Ca2+ at two terminal domains → binding induces conformational changes in calmodulin that expose hydrophobic surfaces
When CaM hydrophobic surfaces are exposed, this conformation is able to do what?
It can bind many cellular signaling proteins such as CaM kinases and CaM kinase activity is altered including its autophosphorylation activity
Receptors like GPCRs and RTKs lead to the activation of what?
Leads to the activation of phospholipases and phospholipid kinases that hydrolyze or phosphorylate various classes of phospholipids (an example is phospholipase C that hydrolyzes PIP2)
Phospholipase C hydrolyzes what bond in PIP2?
The phosphate stays with the polar head group
Phospholipase D hydrolyzes what bond in PIP2?
Leaves the phosphate on the fatty acid chain
Phospholipase A hydrolyzes what bond in PIP2?
Cleaves the fatty acid chain
What is the difference between the various phospholipases?
They all cleave different positions of the phospholipid which means that they all have different substrate specificities
What is the importance of phospholipase C?
It hydrolyzes PIP2 to DAG and IP3
What is PLC𝛽 activated by?
It is activated by interaction with trimeric G proteins (GPCRs)
What is PLC𝛾 activated by?
It is activated by tyrosine phosphorylation (RTKs)
