Retinal, one of several vitamin A compounds serves a vital role in human vision (Tver and Russell, 458). Discovered in 1913, Vitamin A was the first vitamin to be discovered. The Vitamin A group includes the carotenoids, retinol and retinal. Each of these forms plays a significant role in animal vision, and vision is what led to vitamin A’s discovery. During the early 1900s, many researchers were conducting studies on the eyes of animals. They found that if the animals were consuming diets deficient in what are recognized today as vitamin A-rich sources, the animals’ eyes became inflamed and eventually infected. In 1932, scientists discovered beta carotene and found out that the body is able to convert it into vitamin A, and furthermore, it could be used to prevent eye disorders (Somer 18). However, this was merely the discovery of Vitamin A. It wasn’t until 1967, when George Wald, a professor at Harvard University, and his colleagues began to seek an understanding of vision and vitamin A’s role in the vision process that retinal was discovered. Wald’s group studied the protein rhodopsin which is present in the rods. They broke the proteins down into molecular parts and discovered a protein called opsin and an organic chromophore known as retinal (Szaflarski). The structure of retinal is pictured below. Retinal is an aldehyde, as the –al suffix suggests. By definition, an aldehyde must contain a carbon which is double-bonded to an oxygen atom, but that same carbon must also be bonded to at least one hydrogen atom. In order for this to occur, the afore-mentioned carbon must be on the end of a carbon chain. Otherwise, it would not be able to bond to a hydrogen atom. As one can see in the drawing on the following page, the carbon on the right fits the description. Thus it is an aldehyde. Additionally, there is a chain of carbons containing some double bonds. Those double bonds are indicative of the alkene functional group (Stoker 444).
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Flowers, Frances, "Retinal: The Biological Role and Significance" (2011). Academic Symposium of Undergraduate Scholarship. Paper 9.