There are four known forces that are involved in evolution:

1)mutation,

2) genetic drift

3) gene flow or migration

4) selection.

TLS Online TPP Program

#Id: 9314

#XL - T Zoology

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

#XL - T Zoology

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

TLS Online TPP Program

#Id: 9316

#XL - T Zoology

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

#XL - T Zoology

TLS Online TPP Program

#Id: 9318

#XL - T Zoology

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

#XL - T Zoology

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