What's Reflected, What's Absorbed

I've been on a serious pigment kick lately (reinforced by my little art excursion last night and my review of all of the fall leaf literature), and rhodopsin came to mind, a light absorbing pigment found in animal eyes, archaea and bacteria (often referred to as bacteriorhodopsin in the case of the archaea).

While chlorophyll is capable of absorbing red and blue light from the sun for much of the year (all year for evergreens), bacteriorhodopsin can absorb wavelengths that much of the plant world reflects, from 490 - 550 nm, or the color green (see chart below).

Bacteriorhodopsin is particularly widespread in the oceans. The depth of the photosynthesizing organism determines the wavelength of light most strongly absorbed; in shallow, churning waters, bacteria will absorb green wavelengths more readily, while blue wavelengths are favored in deeper waters.

When light strikes bacteriorhodopsin, it causes a change in the shape (conformation) of the protein complex, which in turn powers a biological cornerstone: the proton pump. Protons are moved between membranes, creating a gradient of pH and an energy potential. The energy created is in turn used to pluck phosphorus from a cell's cytoplasm to complete the most well-known energy transporting molecules, adenosine triphosphate, or ATP. ATP then can be transported from there for use as energy in any other system.

Photosynthesis runs on different organic systems in the archea, leading biologists to believe that photosynthetic machinery must have evolved twice: once in the archaea, and once in bacteria (cyano; the discrepancies lie in the ETC and in the fixation of CO₂ into glucose).