Signal Transduction 2: G Protein-coupled Receptor Signal Transduction

Question 1

What are the three main types of transmembrane receptors?

Answer 1

1. G-protein coupled receptors (GPCRS)
2. Receptor tyrosine kinase (RTKs)
3. Ligand-gated ion channel receptors

Question 2

What are G protein coupled receptors?

Answer 2

Receptors that work with the help of a G protein (and second messengers)

Question 3

What is receptor tyrosine kinase?

Answer 3

Receptors that attach phosphates to tyrosines to signal (phosphorylation cascades etc)

Question 4

What are ligand-gated ion channel receptors?

Answer 4

A signal molecule binds as slogans to the receptor, opening the receptor gate, allowing specific ions (eg Na or Ca) to pass through a channel in the receptor in the cell

Ligand signals

Question 5

What are intracellular receptors?

Answer 5

Found in the cytoplasm or nucleus of target cells and are for small or hydrophobic chemical messengers that can readily cross the membrane to activate them (e.g steroid and thyroid hormones of animals- there are fewer of these receptors)

Question 6

What sort of receptor could epinephrine bind to on a GPCR?

Answer 6

B-adrenergic receptor

Question 7

Whet sort of things can bind to a g-protein?

Answer 7

A lot; light, Ca, small microbes: amino acids, fatty acids, nucleotides, amines, prostaglandins, peptide, proteins (TSH, LH, FSH, chemokines)

Question 8

When are GPCRS active?

Answer 8

At the cell surface where their hormone can access them

Question 9

What are the key structural features of a G-protein?

Answer 9

7 transmembrane regions (serpentine)
Extra cellular N-terminus
Intracellular C-terminus

Question 10

What does transmitting messages across a cell membrane involve for the GPCR receptor?

Answer 10

A conformational change (as the receptor is a gate-keeper of cellular activity, control hormone activity at the cell surface)

Question 11

Describe the heterotrimeric G protein?

Answer 11

Has an a-subunit and a B-y dimer

Question 12

What do G proteins bind to?

Answer 12

Guanine nucleotides

Question 13

What is a G protein?

Answer 13

A guanine nucleotide binding protein

Question 14

What is GDP?

Answer 14

Guanosine diphosphate

Question 15

What is GTP?

Answer 15

Guanasine triphosphate

Question 16

What binds to the effector in the G protein cycle?

Answer 16

Alpha GTP which binds to adenylate cyclase to produce cAMP from ATP (aGTP converted to aGDP)

Question 17

What is cyclic adenosine Monophosphate?

Answer 17

A first second messenger which is a common mediator for many hormones

Question 18

What makes cyclic adenosine Monophosphate?

Answer 18

Enzyme adenylate cyclase

Question 19

What does cyclic AMP do?

Answer 19

Converts inactive protein kinase a to active protein kinase A

Question 20

What does active protein kinase a do?

Answer 20

Converts inactive phosphorylase kinase to active phosphorylase kinase

Question 21

What does active phosphorylase kinase do?

Answer 21

Converts inactive glycogen phosphorylase to active glycogen phosphorylase

Question 22

What are the three different classes of G protein?

Answer 22

Gs (stimulatory G protein that activates adenylate cyclase)
Gi (inhibitory G protein, inactivates adenylate cyclase)
Gq (activates a different effector, phospholipase C)

Question 23

What do Gs favour?

Answer 23

Catalytically active form of adenylate cyclase (increases cAMP)

Question 24

What do Gis favour?

Answer 24

More catalytically inactive form of adenylate cyclase (decreases cAMP)

Question 25

What do Gs and Gi allow for?

Answer 25

Opposing biological effects

Question 26

What do Gi and Gs regulate?

Answer 26

PKA activity, via controlling cAMP levels

Question 27

What receptor does Gi act on?

Answer 27

Inhibitory GPCR

Question 28

Main steps in signal transduction pathways?

Answer 28

G protein
cAMP
protein kinase A
Phosphorylation events