The most useful range for proteins is above 230 nm, where there are absorptions from aromatic side chains.

TLS Online TPP Program

#Id: 9313

#Unit 4. Cell Communication and Cell Signaling

Nonselective cation channels open in response to binding of the second messenger cGMP (cGMP-gated channels)

TLS Online TPP Program

#Id: 9314

#Unit 4. Cell Communication and Cell Signaling

3 or 4 cGMP molecules must bind to each channel in order to open it; because of this cooperative allosteric interaction, channel opening is very sensitive to small changes in cGMP levels.

TLS Online TPP Program

#Id: 9315

#Unit 4. Cell Communication and Cell Signaling

In resting rod cells high cGMP concentration generated from GTP catalyzed by guanylyl cyclase.

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