G-Proteins in Sensory Perception

Question 1

What are the membrane discs within the outer segments of rod cells and highly enriched in light-sensing proteins known as?

Answer 1

Rhodopsins

Question 2

What are Rhodopsins?

Answer 2

Light sensing G-Protein Coupled Receptors (GCPRs) that are activated by photons

Question 3

What are Rhodopsins made up of?

Answer 3

Chromophore called retinal covalently linked to a protein called opsin

Question 4

TRUE OR FALSE:
Rhodopsins have distinct light absorbance spectra

Answer 4

True

Question 5

What is the name of the G-Protein that Rhodopsins 7-TMR is coupled to?

Answer 5

Transducin

Question 6

How is Transducin activated?

Answer 6

GDP-GTP exchange

Question 7

What is the function of Transducin?

Answer 7

Stimulates phosphodiesterase which cleaves cGMP to GMP

Question 8

What is the function of cGMP?

Answer 8

Stimulates the opening of Na+ channels (depolarisation)

Question 9

What is the mechanism of action of Visual Phototransduction Pathway?

Answer 9

1. Photon activates Rhodopsin (conformational change)
2. Transducin activated (GDP to GTP)
3. GTP activated alpha-subunit activates phosphodiesterase
4. Activated phosphodiesterase cleaves cGMP to GMP (closes Na+ channels)
5. Reduced cGMP causes Guanylyl Cyclase to synthesise more cGMP (Na+ channels open)

Question 10

What does activation of the Olfactory G-Protein α-subunit (Gαolf) stimulate?

Answer 10

Activity of adenylyl cyclase isoenzyme to generate cAMP

Question 11

What is the function of cAMP in Olfactory Receptor Signal Transduction?

Answer 11

Opens ion channels to allow influx of Na+ into olfactory neuron (action potential)