Continuing in the vein of biochemistry applications, there are very interesting “Impact on Biochemistry” sections in the Atkin’s Physical Chemistry textbook. For this post I chose the section on ‘Vision’ as it serves to edify oneself on the biochemical basis of arguably the most cherished of our perceptory functions, that which is scientifically known as opthalmoception.
Responsible for vision, the eye is a photochemical organ that transduces light energy into electrical energy that travels along neurons. The presence of a type of protein known as rhodopsin is central to this process.Photons enter the eye through the cornea,pass through the ocular fluid before falling on the retina. Approximately 57% of photons that enter the eye reach the retina whereupon the chromosphore of a rhodopsin molecule facilitates an excited transition state. The free 11-cis- retinal molecule(rhopdopsin consists of this molecule and opsin) abosorbs in the ultraviolet,but attachment to opsin shifts the absorption into the visible region. The premise of further complex interactions is that photoisomerization of the 11-cis-molecule occurs and an intermediate known as metarhodopsin II is formed. A biochemical cascade follows in which activation of a protein known as transducin results in the hydrolysis of cGMP to GMP. The net effect is closure of ion channels and a creation of an electric potential. The pulse of the electric potential travels through the optic nerve, into the optic cortex , where it is interpreted as a signal and incorporated into a web of events that we perceive as vision.
Reference: Atkins,Peter and Julio de Paula. 2010. Atkins’ Physical Chemistry. United States: W.H. Freeman and Company.