3.3 Receptors

Question 1

why is there a membrane potential where the cytosol is more negatively charged

Answer 1

1) cytosol contains abundance of negatively charge proteins whereas the extracellular fluid contains relatively few
2) NaK ATPase takes away 3 Na+ but only brings in 2 K+

Question 2

describe binding assay on a filter steps

Answer 2

1) isolate cell/membrane
2) add radioactive ligand to the membranes
3) pass through a filter
4) wash off unbound ligand
5) measure bound reactivity

Question 3

draw ligand binding assay curve

Answer 3

slide 8

Question 4

how do you determine the nonspecific binding curve in ligand binding assay

Answer 4

1) flood receptors with non-radioactive ligands to saturate
2) wash off with buffer
3) then add radioactive ligands (will only be non-specific binding)
4) measure radioactivity

Question 5

what is Kd

Answer 5

Koff/Kon

- lower Kd = higher affinity of ligand to receptor

Question 6

what are the two mathematical things that make Kd low

Answer 6

1) High Kon

2) Low Koff

Question 7

GPCR

Answer 7

cell-surface receptor (G-Protein Coupled Receptor)

Question 8

B2-adrenergic receptor

Answer 8

cell-surface receptor protein with 7 TM domain that binds to adrenaline on extracellular

Question 9

how does B2-adrenergic receptor shift when bound to adrenaline

Answer 9

TM5 shifts 2A in

TM6 shifts 14A out

Question 10

effect of ligand on GPCR conformations

Answer 10

B2AR ubound, eqm more towards closed

• binding of agonist moves equilibrium towards open
• G-protein can bind on cytosolic side

Question 11

described G-coupled receptor action action of adenylyl cyclase

Answer 11

1) Gs bound with GDP, can’t activate adenylyl cyclase
2) contact of Gs with hormone receptor displaces GDP with GTP
3) GS dissociates into a and Bg and activates adenylyl cyclase
4) internal GTPase hydrolyzes GTP and turns itself off
5) a subunit associates with the Bg subunit

Question 12

what is adenylate cyclase for

Answer 12

catalyzes formation of cAMP which:
1) activates PKA for phosphorylation of cellular proteins such as kinases which can activate other proteins for process such as glycogen breakdown

Question 13

what is the effect of cholera on Gs of the GPCR action of the B-adrenergic receptor

Answer 13

blocks GTPase activity that normally inactivates the Gs

Question 14

what causes enzymes are attributed to desensitization to epinephrine of B2-adrenergic receptor

Answer 14

1) BARK - B2-adrenergic protein kinase (phosphorylates Ser of receptor)
2) B-arrestin - binds to carboxylated terminal of the receptor

Question 15

muscarinic receptor

Answer 15

• reduces frequency of muscle contraction
• muscarinic-acetylcholine receptor coupled to Gai protein
• GDP displaced by ATP
• leads to efflux of K+ ions from cytosol which hyperpolarizes membrane

Question 16

IP3 pathway steps - Ca2+ (4)

Answer 16

1) phospholipase cleaves PIP2 to generate IP3 and diacylglycerol
2) IP3 activates Ca2+ release channels (receptor mediated channel)
3) Ca2+ stored in the ER released into cytosol
4) Ca2+ activates a protein Kinase for something

Question 17

IP3 pathway steps NO (4)

Answer 17

NO synthesized inside cell in response to acetylcholine

• diffuses across tissue
• activates NO receptor with cGMP activity
• increase cGMP which activates protein kinase G
• vasodilation and more blood flow to heart