PPT 2

Question 1

What are the 3 factors in receptor concept

Answer 1

1. Receptors determine relations between dose/concentration of drug and pharmacologic effects (receptor affinity (Kd) determines dose)
2. Receptors are responsible for selectivity of drug action
3. Receptors mediate actions of agonists and antagonists

Question 2

What are orphan receptors?

Answer 2

Receptors that have been identified but we don’t know what binds to it (no known endogenous ligand)

Question 3

What are the 3 components of cell signaling?

Answer 3

1. Signal
2. Receptor
3. Effector

If secondary messaging - also has signal transduction proteins and secondary messengers

Question 4

What are the 2 consequences of hormones regulating gene expression?

Answer 4

Lag period - time it takes to make new proteins
Persistence (effects can continue for hours-days)

Question 5

Where can receptor proteins be located?

Answer 5

In the cell or cell membrane

Question 6

Define coupling

Answer 6

the overall transduction process that links drug occupancy of receptors and pharmacologic response

Question 7

How is the efficiency of coupling determined?

Answer 7

Conformational change, downstream cellular response, and dose response (number of receptors bound - linear, or strength of signal transduction cascade - multiplied response)

Question 8

Describe the phosphorylation cascade

Answer 8

Ligand binding → Receptor activation (change of conformation) → First protein (kinase) activation → Subsequent protein (kinase) activation (amplification) → Effector protein activation → Cellular response

Question 9

What are the 5 mechanisms of transmembrane signaling?

Answer 9

1. Lipid soluble - intracellular
2. Enzymatic activity allosteric
3. Catalytic
4. Ion channels
5. GPCRs

Question 10

What binds to the alpha portion of the G protein ?

Answer 10

Guanine nucleotide (GTP) - active or GDP (inactive)

Question 11

What makes G-proteins trimeric?

Answer 11

3 different amino acid strands that function together to form G-protein
Alpha - binds to GDP (inactive) or GTP (active)
Beta and gamma - help binding to receptor itself

Question 12

What receptors are intracellular?

Answer 12

Lipid soluble - uncharged
Gasses - easily diffuses through membrane

Question 13

What is the motif of every GPCR?

Answer 13

Have 7 trans-membrane alpha helices

Question 14

What are the steps to the GPCR cascade?

Answer 14

1. Drug binds to receptor - activates alpha subunit of G protein (conformation change)
2. G protein releases GDP and binds GTP
3. G protein activates effector protein
4. Secondary messenger cascade or ion conductance

Question 15

What makes a GPCR response fast vs slow?

Answer 15

Fast - rapid desensitization, metabotropic ion channels
Slow - secondary messenger (transcription factor activation)

Question 16

What is the most important part of the G protein?

Answer 16

Alpha subunit - activates effector

Question 17

Differentiate between desensitization and resensitization

Answer 17

• When first give agonist, response jumps up, peaks, then declines (muted response with same amount of agonist) - desensitization
• Stop giving agonist, then wait, then give agonist again → see same response - resensitization

Question 18

Describe the steps to the desensitization process

Answer 18

1. Drug binds to receptor → promotes receptor interaction with G proteins in cytoplasm (closed → open conformation)
2. Agonist-activated receptors phosphorylated by G protein-coupled receptor kinase (GPK), preventing receptor interaction with G protein → attracts beta-arestin (B-Arr)
3. B-Arr receptor complex binds to coated pits, promoting receptor internalization
4. 2 possibilities:
   Possibility 1 - resensitization (Drug falls off receptor→ phosphatase dephosphorylates receptor and receptor recyles back to cell membrane)
   Possibility 2 → degradation (Can’t get drug off of receptor → lysosome merges with drug/receptor complex → enzymes from lysosome degrade receptor)

Question 19

Why would a receptor be degraded instead of resensitized (recycled)?

Answer 19

Repeated or prolonged exposure of cells to agonist favors degradation → promoting receptor down-regulation rather than resensitization

Question 20

How does beta-arestin work?

Answer 20

Beta-arestin is a protein that binds to -OH groups when receptor in open conformation for long time (prolonged binding - i.e. covalent bonds) and binds to coated pits, preventing G protein from rebinding

Question 21

How does the coated pit engulf the receptor complex?

Answer 21

Clathrin coated pit (endocytosis) drags whole receptor with bound drug and beta-arestin into cell

Question 22

Differentiate between kinase and phosphatase

Answer 22

Kinase attaches phosphate group to protein
Phosphatase strips away phosphate group from protein

Question 23

How do RTKs work?

Answer 23

Receptor tyrosine kinases:
1. Ligands bind to receptors, cause conformation change, and dimerization of 2 receptors
2. RTK activated by dimers and phosphorylates tyrosines on receptor dimer from ATP
3. Docking sites for downstream signaling molecules activated

Question 24

How many ATP are necessary for RTK phosphorylation?

Answer 24

6 - or as many as OH groups

Question 25

What are the 2 signal types for ion channels?

Answer 25

Ligand and voltage gated

Question 26

How are voltage-gated ion channels activated?

Answer 26

Change in voltage activates channel; no drug binding, activated by change in voltage

Question 27

Where are voltage-gated ion channels found?

Answer 27

-Found in excitable cells (neurons, muscle, endocrine cells)

Question 28

When are voltage-gated ion channels open vs closed?

Answer 28

Closed at resting membrane potential Open at threshold

Question 29

Describe the different conformations of the voltage-gated ion channels? Which gates are open when?

Answer 29

Closed - gate 1 closed, 2 open Activated - both gates open Inactivated - gate 2 closes, gate 1 open Deactivated - both closed

Question 30

Differentiate ionotropic from metabotropic ligand-gated ion channels

Answer 30

Ionotropic - Ligand binding site and channel on same protein Metabotropic - Ligand activates GPCR, second messenger activity opens channel

Question 31

What is the most common second messenger?

Answer 31

cAMP (cyclic adenosine monophosphate)

Question 32

Dose response is related to

Answer 32

Amount of receptors bound and or the strength of signal transduction cascade

Question 33

2/3 of all non-antibiotic drugs are activated by

Answer 33

GPCRs

Question 34

Sodium channels are considered to be

Answer 34

fast

Question 35

Calcium ion channels are considered to be

Answer 35

slow

Question 36

The example in lecture of a metabotropic ligand gated ion channel is in the ____________ system

Answer 36

olfactory

Question 37

Receptors inside the cell can only be easily activated by ________

Answer 37

something that is lipid soluble and can freely diffuse through the cell membrane (ex Gasses and steroid hormones)