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 AlsoCarbon Dioxide; Water

Chlorophyll

Chlorophyll is a green pigment contained in the foliage of plants, giving them their notable coloration. This pigment is responsible for absorbing sunlight required for the production of sugar molecules, and ultimately of all biochemicals, in the plant.

Chlorophyll is found in the thylakoid sacs of the chloroplast. The chloroplast is a specialized part of the cell that functions as an organelle. Once the appropriate wavelengths of light are absorbed by the chlorophyll into the thylakoid sacs, the important process of photosynthesis is able to begin. In photosynthesis, the chloroplast absorbs light energy, and converts it into the chemical energy of simple sugars.

The chlorophyll molecule is composed of one central porphyrin ring and side chains. A magnesium atom is found at the center of the porphyrin ring—a complex multi-ring structure composed of carbon, hydrogen, nitrogen, and oxygen atoms. The conjugated double bonds of this structure allow the chlorophyll molecule to absorb energy from sunlight.

Vascular plants, which can absorb and conduct moisture and nutrients through specialized systems, have two different types of chlorophyll. The two types of chlorophyll, designated as chlorophyll a and b, differ slightly in chemical makeup and in color. These chlorophyll molecules are associated with specialized proteins that are able to penetrate into or span the membrane of the thylakoid sac.

When a chlorophyll molecule absorbs light energy, it becomes an excited state, which allows the initial chain reaction of photosynthesis to occur. The pigment molecules cluster together in what is called a photosynthetic unit. Several hundred chlorophyll a and chlorophyll b molecules are found in one photosynthetic unit.

A photosynthetic unit absorbs light energy. Red and blue wavelengths of light are absorbed. The chlorophyll cannot absorb green light, so the light is reflected, making the plant appear green. Once the light energy penetrates these pigment molecules, the energy is passed to one chlorophyll molecule, called the reaction center chlorophyll. When this molecule becomes excited, the light reactions of photosynthesis can proceed. With carbon dioxide, water, and the help of specialized enzymes, the light energy absorbed creates chemical energy in a form the cell can use to carry on its processes.

In addition to chlorophyll, there are other pigments known as accessory pigments that are able to absorb light where the chlorophyll is unable to. Carotenoids, like B-carotenoid, are also located in the thylakoid membrane. Carotenoids give carrots and some autumn leaves their color. Several different pigments are found in the chloroplasts of algae, bacteria, and diatoms, coloring them varying shades of red, orange, blue, and violet.

See also Plant pigment.

Chlorophyll

Chlorophyll is a green pigment contained in the foliage of plants, giving them their notable coloration. This pigment is responsible for absorbing sunlight required for the production of sugar molecules, and ultimately of all biochemicals, in the plant .

Chlorophyll is found in the thylakoid sacs of the chloroplast . The chloroplast is a specialized part of the cell that functions as an organelle. Once the appropriate wavelengths of light are absorbed by the chlorophyll into the thylakoid sacs, the important process of photosynthesis is able to begin. In photosynthesis, the chloroplast absorbs light energy , and converts it into the chemical energy of simple sugars.

Vascular plants, which can absorb and conduct moisture and nutrients through specialized systems, have two different types of chlorophyll. The two types of chlorophyll, designated as chlorophyll a and b, differ slightly in chemical makeup and in color . These chlorophyll molecules are associated with specialized proteins that are able to penetrate into or span the membrane of the thylakoid sac.

When a chlorophyll molecule absorbs light energy, it becomes an excited state, which allows the initial chain reaction of photosynthesis to occur. The pigment molecules cluster together in what is called a photosynthetic unit. Several hundred chlorophyll a and chlorophyll b molecules are found in one photosynthetic unit.

A photosynthetic unit absorbs light energy. Red and blue wavelengths of light are absorbed. Green light cannot be absorbed by the chlorophyll and the light is reflected, making the plant appear green. Once the light energy penetrates these pigment molecules, the energy is passed to one chlorophyll molecule, called the reaction center chlorophyll. When this molecule becomes excited, the light reactions of photosynthesis can proceed. With carbon dioxide , water , and the help of specialized enzymes, the light energy absorbed creates chemical energy in a form the cell can use to carry on its processes.

In addition to chlorophyll, there are other pigments known as accessory pigments that are able to absorb light where the chlorophyll is unable to. Carotenoids, like B-carotenoid, are also located in the thylakoid membrane. Carotenoids give carrots and some autumn leaves their color. Several different pigments are found in the chloroplasts of algae , bacteria , and diatoms , coloring them varying shades of red, orange, blue, and violet.

See also Plant pigment.

Chlorophyll

All forms of life on the surface of Earth are powered, directly or indirectly, by absorption of the energy in sunlight by chlorophyll molecules in plant cells. The subsequent processes of photosynthesis convert light energy to electrical and then chemical energy, which the cell uses for growth. The minimal absorption of green light by chlorophyll causes plants to have a green color (see accompanying graph).

Chlorophylls are cyclic tetrapyrroles, that is, molecules made by connecting four 5-membered pyrrole rings into a macrocycle. The initial biosynthetic precursor, 5-aminolevulinic acid (ALA), is made from the abundant amino acid glutamic acid. Condensation of two ALA molecules produces the 5-membered ring compound porphobilinogen. Four of these molecules are joined into a large ring structure, some of the side chains are modified, and the compound is oxidized to generate the fully conjugated double-bond arrangement that allows efficient absorption of light energy. At this stage, Mg²⁺ is inserted into the center of the large ring structure, and the fifth ring is formed.

The long hydrocarbon side chain causes chlorophyll to act as a lipid, allowing it to become embedded in thylakoid membranes. Chlorophyll a can be oxidized to chlorophyll b, which differs only in the presence of an alde-hyde group on ring B. All chlorophyll molecules are bound to protein molecules and incorporated into complexes that allow energy absorbed by the molecules to be trapped in reaction centers of photosynthesis. In eukaryotic photosynthetic organisms, all these reactions occur in the chloroplast .

Other forms of chlorophyll also are found in nature. Some families of algae contain chlorophyll c, which does not have a long lipid tail and differs in several other respects. Chlorophyll d, which was found recently as the major chlorophyll in a photosynthetic prokaryote living inside ascidians in the Pacific Ocean, is similar to chlorophyll b but with the aldehyde on ring A. Bacteriochlorophylls, possibly the evolutionary ancestors of chlorophylls, occur in photosynthetic bacteria. Unlike other chlorophylls, bacteriochlorophylls absorb light in the infrared region, near 800 nanometers (nm).

see also Chloroplasts; Photosynthesis, Light Reactions and; Pigments.

J. Kenneth Hoober

Bibliography

Beale, Samuel I. "Enzymes of Chlorophyll Biosynthesis." Photosynthesis Research 60 (1999): 43-73.

Chlorophyll

Chlorophyll is a green pigment contained in the foliage of plants, giving them their notable coloration. This pigment is responsible for absorbing sunlight required for the production of sugar molecules, and ultimately of all biochemicals, in the plant.

Chlorophyll is found in the thylakoid sacs of the chloroplast . The chloroplast is a specialized part of the cell that functions as an organelle. Once the appropriate wavelengths of light are absorbed by the chlorophyll into the thylakoid sacs, the important process of photosynthesis is able to begin. In photosynthesis, the chloroplast absorbs light energy, and converts it into the chemical energy of simple sugars.

Vascular plants, which can absorb and conduct moisture and nutrients through specialized systems, have two different types of chlorophyll. The two types of chlorophyll, designated as chlorophyll a and b, differ slightly in chemical makeup and in color. These chlorophyll molecules are associated with specialized proteins that are able to penetrate into or span the membrane of the thylakoid sac.

When a chlorophyll molecule absorbs light energy, it becomes an excited state, which allows the initial chain reaction of photosynthesis to occur. The pigment molecules cluster together in what is called a photosynthetic unit. Several hundred chlorophyll a and chlorophyll b molecules are found in one photosynthetic unit.

A photosynthetic unit absorbs light energy. Red and blue wavelengths of light are absorbed. Green light cannot be absorbed by the chlorophyll and the light is reflected, making the plant appear green. Once the light energy penetrates these pigment molecules, the energy is passed to one chlorophyll molecule, called the reaction center chlorophyll. When this molecule becomes excited, the light reactions of photosynthesis can proceed. With carbon dioxide, water, and the help of specialized enzymes , the light energy absorbed creates chemical energy in a form the cell can use to carry on its processes.

In addition to chlorophyll, there are other pigments known as accessory pigments that are able to absorb light where the chlorophyll is unable to. Carotenoids, like B-carotenoid, are also located in the thylakoid membrane. Carotenoids give carrots and some autumn leaves their color. Several different pigments are found in the chloroplasts of algae, bacteria , and diatoms , coloring them varying shades of red, orange, blue, and violet.

See also Autotrophic bacteria; Blue-green algae