SIGNAL TRANSDUCTION

- from rhodopsin to the visual cortex

For a figure of phototransduction in rod cells, see Nature 2004

The process:

• When light reaches 11-cis-retinal inside the Rhodopsin molecule, it is converted to all-trans-retinal.

• A conformational change in Rhodopsin is brought on, activating the enzyme Transducin.

• The activated Transducin releases GDP and binds GTP.

• The α-subunit of Transducin activates the phosphodiesterase.

• Active phosphodiesterase converts cGMP to non-cyclic GMP. Reduced concentration of cGMP in the cell closes Na⁺ channels, and the cell is hyperpolarised.

• When Transducin has spent its GTP and can no longer activate the phosphodiesterase, Rhodopsin regenerates and the system is again ready for a new photon.