Unit 6 bio part 2
How is a GPCRs activated (2)
1. signal molecule binds and activates receptor
2. GDP disassociates and GTP activates subunit and effector
How is the subunit turned off
hydrolysis of GTP by the subunit inactivates the subunit and causes it to disassociate from the target protein
How long does a G protein signal last
As long as (a) and (by) subunits are free
what are the consequences of disruptions in Ga function (4)
1. cholera - bacterium produces toxin that enters intestinal cells and alters Ga subunit
2. cell is continuously active, prolonged secretion into the gut
3. cough, bacterium colonizes lung, produces pertussin toxin that enters cells and alters Ga subunit
4. prolonged, inappropriate signal that generates coughing
How are ion channels activated (2)
1. signal molecule binds to receptor and activates (a) subunit and (by) complex, ion channel opens
2. GTP -> GDP, inactive G protein causing closed ion channel
what do 2nd messengers do in the activation of G proteins
1. second messenger molecules diffuse to act on intracellular signalling proteins
adrenal cyclase function (2)
1. adrenal cyclase are activated by second messenger molecules
2. cyclic shape turns it on, breaking cyclic shape turns it off
how is adenyl cyclase activated
1. epinephrine acts via a GPCr that activates adenyl cyclase
Can cyclic AMP drive gene transcription
yes it activates PKA that travels down a nuclear pore and activates transcription regulator
Phospholipase C function
It is activated by GPCRs and helps activate PKC with inosital 1,4,5-triphosphate entering ER lumen opening Ca2+ ion channel and Ca2+ acts as a second messenger to activate PKC
What is CA2+ (4)
1. It is a intracellular signal
2. concentrations in the cytoskeleta=on are very low compared to outside the cell
3. cytosolic Ca2+ can be rapidy increased
4. Binding of Ca2+ activates many different proteins
What are enzyme linked receptors
receptors are enzymes themselves or associated with enzymes
How is the receptor tyrosine kinase activated (2)
1. signal molecule in form of a dimer binds to RTK and stimulates the kinase activity
2. active RTK's cause the activation of downstream intracellular signaling pathways
What are RTKs (2)
1. the largest class of enzyme coupled receptors
2. signal proteins recruited to cytosolic tails of RTK activated other downstream signals
Do all RTK's activate the monomeric GTP-binding proteins RTK or Ras
Ras
what is Ras (GTP-binding protein) (4)
1. small monomeric G-protein bound to inner membrane by lipid tail
2. acts as a molecular switch
3. active when bound to GTP, turns off by hydrolyzing it to GDP
4. Sets off relay of signals
What do mutations in Ras lead to
permanently activated proteins
what does uncontrolled growth/division cause
cancer
what is the most commonly mutated gene in human cancer cells
Ras
what is cancer
a failure of cell commmunication