In Drosophila, an example of position effect variegation in the fly eye. 

TLS Online TPP Program

#Id: 9316

#Unit 4. Cell Communication and Cell Signaling

Light absorption by rhodopsin→activation of a cGMP PDE → hydrolyzes cGMP to 5′-GMP→ cGMP levels  drop →channel close →membrane hyperpolarization→reduction in NT release→transmitted to brain

TLS Online TPP Program

#Id: 9317

#Unit 4. Cell Communication and Cell Signaling

TLS Online TPP Program

#Id: 9318

#Unit 4. Cell Communication and Cell Signaling

Rapid termination mechanisms of the Rhodopsin Signalling:

1.GAP that inactivates Gαt·GTP

2.Ca2+ -sensing proteins that activate Guanylate Cyclase

3.Rhodopsin Phosphorylation and Binding of Arrestin

TLS Online TPP Program

#Id: 9319

#Unit 4. Cell Communication and Cell Signaling

Gαt contains an intrinsic GTPase activity by GAP complex, RGS9-Gβ5 triggers the rapid inactivation of the PDE

TLS Online TPP Program

#Id: 9320

#Unit 4. Cell Communication and Cell Signaling

Light-triggered closing of the cGMP-gated cation

channels causes a drop in the cytosolic Ca2+ concentration inside the rod cell.

TLS Online TPP Program

#Id: 9321

#Unit 4. Cell Communication and Cell Signaling

Low intracellular Ca2+ concentration is sensed by a class of Ca2+ -binding proteins known as guanylate cyclase–activating proteins.