Chlorophyll | Research & Encyclopedia Articles

Chlorophyll

Overview

Chlorophyll (KLOR-uh-fill) is the pigment that gives plants, algae, and cyanobacteria their green color. The name comes from a combination of two Greek words, chloros, meaning "green" and phyllon, meaning "leaf." Chlorophyll is the substance that enables plants to create their own food through photosynthesis.

At least five forms of chlorophyll exist. They are:

• chlorophyll a (also known as α-chlorophyll), with a formula of C₅₅H₇₂O₅N₄Mg
• chlorophyll b (also known as β-chlorophyll), with a formula of C₅₅H₇₀O₆N₄Mg
• Chlorophyll c1, with a formula of C₃₅H₃₀O₅N₄Mg
• Chlorophyll c2, with a formula of C₃₅H₂₈O₅N₄Mg
• Chlorophyll d, with a formula of C₅₄H₇₀O₆N₄Mg

Key Facts

Formula:

Varies; see Overview.

Elements:

Carbon, hydrogen, oxygen, nitrogen, magnesium

Compound Type:

Organic

State:

Solid

Molecular Weight:

608.96-907.47 g/mol

Melting Point:

Chlorophyll a: 152.3°C (306.1°F); Chlorophyll b: 125 C (257°F)

Boiling Point:

Not applicable

Solubility:

Chlorophyll a and b are insoluble in water, soluble in alcohol, ether, and oils

Chlorophyll a occurs in all types of plants and in algae. Chlorophyll b is found primarily in land plants. Chlorophyll c1 and chlorophyll c2 are present in various types of algae. Chlorophyll d is found in red algae.

All forms of chlorophyll have a similar chemical structure. They have a complex system of rings made of carbon and nitrogen known as a chlorin ring. The five forms of chlorophyll differ in the chemical groups attached to the chlorin ring. These differences result in slightly different colors of the five chlorophylls.

French chemists Pierre-Joseph Pelletier (1788–1842) and Joseph-Bienaimé Caventou (1795–1877) first isolated chlorophyll in 1817. In 1865, German botanist Julius von Sachs (1832–1897) demonstrated that chlorophyll is responsible for photosynthetic reactions that take place within the cells of leaves. In the early 1900s, Russian chemist Mikhail Tsvett (1872–1920) developed a technique known as chromatography to separate different forms of chlorophyll from each other. In 1929, the German chemist Hans Fischer (1881–1945) determined the complete molecular structure, making possible the first synthesis of the molecule in 1960 by the American chemist Robert Burns Woodward (1917–1979).

Interesting Facts

• The chemical structure of chlorophyll is very similar to that of hemoglobin, the molecule that transports oxygen in the red blood cells of mammals. The major difference between the two is that hemoglobin contains an atom or iron at the center of a large ring compound, while chlorophyll has an atom of magnesium in the same location.
• Leaves contain compounds called carotenoids that are red, orange, and yellow in color. These colors are masked by the green color of chlorophyll. In fall, plants stop producing chlorophyll, and the red, orange, and yellow of carotenoids become visible. Carotenoids do not perform photosynthesis, although they do transmit light energy to chlorophyll, where photosynthesis takes place.

How It Is Made

Plants make chlorophyll in their leaves using materials they have absorbed through their roots and leaves. The synthesis of chlorophyll requires several steps involving complex organic compounds. First, the plant converts a common amino acid, glutamic acid (COOH(CH₂)₂CH(NH₂)COOH) into an alternative form known as 5-aminolevulinic acid (ALA). Two molecules of ALA are then joined to form a ring compound called porphobilinogen. Next, four molecules of porphobilinogen are joined to form an even larger ring structure with side chains. Oxidation of the larger ring structure introduces double bonds in the molecule, giving it the ability to absorb line energy. Finally, a magnesium atom is introduced into the center of the ring and side chains are added to the ring to give it its final chlorophyll configuration.

Common Uses and Potential Hazards

Plants store chlorophyll in their chloroplasts, organelles (small structures) that carry out the steps involved in photosynthesis. Each chloroplast contains many clusters of several hundred chlorophyll molecules called photosynthetic units. When a photosynthetic unit absorbs light energy, chlorophyll molecules move to a higher energy state, initiating the process of photosynthesis. The overall equation for the process of photosynthesis is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

Words to Know

CHLORIN RING

A ring of carbon and nitrogen atoms bonded to each other.

CHROMATOGRAPHY

Process by which a mixture of substances passes through a column consisting of some material that causes the individual components in the mixture to separate from each other.

PHOTOSYNTHESIS

The process by which green plants and some other organisms using the energy in sunlight to convert carbon dioxide and water into carbohydrates and oxygen.

SYNTHESIS

A chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants.

That simple equation does not begin to suggest the complex nature of what happens during photosynthesis. Botanists divide that process into two major series of reactions: the light reactions and the dark reactions. In the light reactions, plants use the energy obtained from sunlight to make two compounds, adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). ATP and NADPH are not themselves components of carbohydrates, the final products of photosynthesis. Instead, they store energy that is used to make possible a series of thirteen different chemical reactions that occur during the dark stage of photosynthesis that result in the conversion of carbon dioxide and water to the simple carbohydrate glucose (C₆H₁₂O₆).

For Further Information

Attenborough, David. The Private Life of Plants. Princeton, NJ: Princeton University Press, 1995.

Buchanan, B. B., W. Gruissem, and R. L. Jones. Biochemistry and Molecular Biology of Plants. Rockville, MD: American Society of Plant Physiologists, 2000.

"Chlorophyll and Chlorophyllin." The Linus Pauling Institute Micronutrient Information Center. http://lpi.oregonstate.edu/infocenter/phytochemicals/chlorophylls/ (accessed on October 3, 2005).

May, Paul. "Chlorophyll." School of Chemistry, University of Bristol. http://www.chm.bris.ac.uk/motm/chlorophyll/chlorophyll_h.htm (accessed on October 3, 2005).

Steer, James. "Structure and Reactions of Chlorophyll." http://www.ch.ic.ac.uk/local/projects/steer/chloro.htm (accessed on October 3, 2005).

See Also

Carbon Dioxide; Water

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