Lec 10

Question 1

Metabotropic receptors

Answer 1

Slower processes that have longer and more diverse metabolic effects

Question 2

Metabotropic receptor mechanism

Answer 2

G-protein coupled receptor (GPCR)

Act as molecular switches

When receptor is bound to GTP, they are ‘on’

When receptor is bound to GDP, they are ‘off’

Question 3

2nd messenger

Answer 3

Intercellular signals

Question 4

1st messenger

Answer 4

The neurotransmitter

Question 5

Why is the G-protein the lazy middle man

Answer 5

It acts on the effector protein which sends the second messenger to open an ion channel

Question 6

How may domains do G-coupled receptors have

Answer 6

7 transmembrane domains (TM1-7)

Question 7

Where does the G-protein generally bind to

Answer 7

T5-T7 region, but sometimes includes T3 and/or T4

Question 8

G protein subunits

Answer 8

Alpha
Beta
Gamma

Question 9

The receptor being off means

Answer 9

GDP is bound to a subunit

Question 10

The receptor being on means

Answer 10

GDP has been exchanged with GTP

G-protein separated into alpha and beta/gamma

Question 11

1st type of metabotropic receptor sequence

Answer 11

G-protein opens an ion channel without a 2nd messenger

Question 12

1st type of metabotropic receptor sequence steps (6)

Answer 12

1) ACh binds to the receptor
2) GDP replaces GTP on the alpha subunit of the G-protein
3)G-protein separates into alpha and beta/gamma subunits
4)Beta/gamma subunit binds to K+ channel
5)K+ flows out of cell causing IPSPs
6)Heart rate decreases

Question 13

2nd type of metabotropic receptor sequence

Answer 13

G-protein coupled receptor uses cyclic AMP as a second messenger

Question 14

2nd type of metabotropic receptor sequence steps (7)

Answer 14

1) Norepinephrine binds to receptor
2)G protein “finds” an activated receptor, binds to it, and is itself activated as GDP is replaced with the GTP subunit
3)G-protein separates and the alpha-subunit activates adenylate cyclase
4) This converts ATP to cyclic AMP which activates a protein kinase A which can phosphorylate: (5, 6 or 7)

5)Membrane ion channel proteins causing them to open or close
6)Cytoplasmic proteins causing their enzymes to be activated or deactivated
7)Nuclear proteins causing gene expression

Question 15

3rd type of metabotropic receptor sequence

Answer 15

G-protein coupled receptor uses cyclic GMP as a 2nd messenger

Question 16

3rd type of metabotropic receptor sequence steps (4)

Answer 16

1)Rhodopsin molecules in the disc membrane absorb light and are activated
2)The activated rhodopsin stimulates a G protein transducin, GTP replaces GDP which releases the alpha subunit, which in turn activates cGMP phosphodiesterase
3)The phosphodiesterase catalyze the breakdown cGMP to 5’-GMP
4)As the cGMP concentration decreases, cGMP concentration decreases, cGMP detaches from the cation channels, which close

Question 17

4th type of metabotropic receptor sequence

Answer 17

G-protein coupled receptor uses a phospholipase C pathway to generate 2nd messengers- IP3, DAG and in turn, Ca2+

Question 18

4th type of metabotropic receptor sequence steps

Answer 18

C