Chlorophyll Function and Structure
Chlorophyll comes from the Greek words meaning "green leaf." Most plant cells contain yellow, orange, and red pigments, but these are obscured by the green pigment known as chlorophyll. It is in autumn, when woody plants stop producing chlorophyll, that the other colors become visible.
Chlorophyll was first isolated by French chemists in 1817. Pierre-Joseph Pelletier and his research partner Joseph-Bienaimé Caventou (1795-1877) extracted chlorophyll from green plants, but were unable to find any immediate use for it. Pelletier and Caventou were more interested in substances that could be used as medicines and later discovered such drugs as brucine, quinine, and strychnine.
About fifty years later, scientists learned of chlorophyll's role in plant life. Although Dutch scientist Jan Ingen Housz had described the process of photosynthesis in the late 1700s, no one knew exactly how green plants converted sunlight to food. In 1865 German botanist Julius von Sachs (1832-1897) discovered that chlorophyll catalyzes, or promotes, photosynthetic reactions in the presence of light. Sachs showed that chlorophyll is confined to certain specialized structures inside the cell, which he termed chloroplasts, and all the essential processes of photosynthesis are carried out within these structures. When a leaf is exposed to light, it is in the chloroplasts that the grains of starch, or carbohydrates, first appear.
Just after the turn of the century, Russian scientist Mikhail Tsvett (1872-1920) developed the laboratory technique of chromatography, which separates individual chemicals by color so that they can be identified. Tsvett used chromatography to isolate different types of chlorophyll, but few other scientists knew about the technique. It was popularized a few years later by Richard Willstätter, who found that only two major types of chlorophyll exist in land plants: the blue-green , or "a" type, and the yellow-green, or "b" type. Scientists now know that there are three more forms of chlorophyll, the "c," "d," and "e" types.
Willstätter also discovered that chlorophyll's structure is very similar to that of hemoglobin, the red pigment in blood. Continuing Willstätter's work, German chemist Hans Fischer examined the subtle differences between chlorophyll and hemoglobin molecules in the 1930s and worked out chlorophyll's complete structure. His discovery that chlorophyll contains magnesium was the first indication of the chemical's importance as a plant nutrient (the main difference between chlorophyll and hemoglobin is the fact that chlorophyll carries magnesium while hemoglobin carries iron). During the 1950s American biochemist Melvin Calvin confirmed that a light reaction involving chlorophyll instantly captures the sunlight and converts it into chemical energy. Robert Burns Woodward, an American chemist, synthesized the complex chlorophyll molecule in 1960.
This is the complete article, containing 427 words
(approx. 1 page at 300 words per page).
