Chlorophyll: Structure, Types, and Functions

Chlorophyll is a green organic pigment present in the thylakoid membrane of chloroplast. The presence of chlorophyll and chloroplasts are distinctive features of plant cells, algae and cyanobacteria (blue-green algae).

• Green plants synthesize their own food in the presence of sunlight and chlorophyll by the process of photosynthesis.
• However, chlorophyll plays a major role during photosynthesis by converting light energy into chemical energy.
• The plants involved in the process of photosynthesis are called autotrophs. 

Apart from chlorophyll, anthocyanins, carotenoids and xanthophylls are also present in green plants which play an important role in the photosynthesis process. In this article, we will discuss the complex structure, formula, types and functions of chlorophyll in more detail.

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What is Chlorophyll?

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The word "chlorophyll" is derived from two Greek words: chloros, meaning "light green," and phylon, meaning "leaves." Thus, chlorophyll can be defined as:

It is essential for photosynthesis, which is the process of converting light energy into a chemical form so that living organisms can use it. Chlorophyll absorbs energy from sunlight, which is then utilized to convert carbon dioxide into carbohydrates and gives oxygen as the byproduct.

• These pigments are found in all green sections of plants and are organized in the chloroplasts of each cell.
• The chlorophyll structure is similar to that of hemoglobin present in the red blood cells of mammals and other animals.
• They absorb light from the sun, specifically red and blue light, and transform it into chemical energy.

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Structure of Chlorophyll

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The chlorophyll molecule consists of a magnesium atom placed at the center, encircled by a nitrogen-containing structure known as a porphyrin ring. Since, it is an organic compound, it is represented by a formula. The chlorophyll formula is written as C₅₅H₇₂O₅N₄Mg. The complex structure of chlorophyll is made up of three constituent elements: 

• Magnesium Atom: The magnesium atom is present in the center of the chlorophyll structure. It plays a major role in the absorption of sunlight during the process of photosynthesis.
• Porphyrin Ring: A ring structure composed of nitrogen and four pyrrole rings together form a porphyrin ring. It is involved in the process of energy conversion.
• Phytol Chain: The last component of chlorophyll that is attached to the porphyrin ring is called the phytol chain. It contains long carbon chains that play a major role during chlorophyll degradation or leaf senescence.

Chlorophyll Structure

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Location of Chlorophyll

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Chlorophyll has a fixed location in green plants and algae and it is a small pancake-like structure present in the chloroplast called the thylakoid membrane. Grana are a structure found in chloroplasts made up of stacks of flattened discs known as thylakoids. These thylakoids contain the photosystem, which contains photosynthetic pigments. It is also present in the stroma of chloroplast.

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Role of Chlorophyll

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The main function of chlorophyll is in photosynthesis, in which plants receive light energy and transform it into chemical energy.

• Carbohydrates are synthesized using sunlight, carbon dioxide, and water.
• Almost all green plants and certain organisms, such as cyanobacteria and algae, have chlorophyll.
• In the photosynthesis process, chlorophyll absorbs sunlight of various wavelengths.
• It synthesizes carbohydrates with the help of carbon dioxide and water.
• In chlorophyll, a magnesium ion is abundant, forming a large ring-like structure called chlorine.
• A unique characteristic of chlorine rings is that they are heterocyclic compounds formed from pyrrole.

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Types of Chlorophyll

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There are two types of chlorophyll in green plants: chlorophyll a and chlorophyll b. Each kind of chlorophyll absorbs light at slightly different wavelengths. Chlorophyll c is present in some marine algae. Chlorophyll d is found in certain cyanobacteria species. Chlorophyll e is very uncommon, appearing exclusively in certain golden algae. The different types of chlorophyll are:

Chlorophyll A

Chlorophyll A is mainly found in higher plants and green algae. It is the primary light-harvesting pigment found in all photosynthetic organisms. 

• This pigment absorbs the majority of the wavelength contained in the blue-violet and orange-red sections of the light and reflects the yellow-green light, giving such parts a green color.
• The molecular formula of Chlorophyll A is C₅₅H₇₂O₅N₄Mg.

Structure of Chlorophyll A

Chlorophyll B

Chlorophyll B is also found in higher plants and green algae. It acts as a light-harvesting pigment, transmitting light excitation to chlorophyll A.

• In oxygenic photosynthetic organisms, chlorophyll b is the second most prevalent chlorophyll.
• This pigment absorbs the majority of the wavelength contained in the blue section of the light.
• The concentration of chlorophyll b may grow as organisms adapt, and as chlorophyll b concentration increases, so does the spectrum of wavelengths absorbed by the organisms.
• The molecular formula of Chlorophyll B is C₅₅H₇₀O₆N₄Mg.

Structure of Chlorophyll B

Chlorophyll C

Chlorophyll C is found in brown algae, diatoms, and dinoflagellates. It is a secondary pigment present in certain marine algae and is less abundant than chlorophyll a and b.

• It absorbs light in the 447-520 nm wavelength range and thus creates a blue-green hue.
• Chlorophyll pigments in chlorophyll c are further classified as chlorophyll c₁, chlorophyll c₂, and chlorophyll c₃.
• The molecular formula of Chlorophyll C is C₃₅H₂₈O₅N₄Mg.

Structure of Chlorophyll C

Chlorophyll D

Chlorophyll D is found in cyanobacteria and red algae. Chlorophyll D is one of the rare kinds of chlorophyll.

• It is primarily found in marine algae and photosynthetic organisms living in deep water where light does not penetrate very well.
• It absorbs far-red wavelengths beyond the optical spectrum as well as some blue-green wavelengths.
• The molecular formula of Chlorophyll D is C₅₄H₇₀O₆N₄Mg.

Chlorophyll E

Chlorophyll E is found in some golden algae such as Vaucheria hamata, and Tribonema bombycid.

• Chlorophyll E is one of the rare kinds of chlorophyll and serves as an accessory pigment in a variety of photosynthetic species.
• It was discovered recently, hence the structure and the molecular formula are not defined yet.

Chlorophyll F

Chlorophyll F is found in cyanobacteria. Chlorophyll F is found in aquatic creatures and allows for the absorption of infrared light present in the red region. 

• The precise role of chlorophyll f in photosynthesis is unknown, although evidence of it serving as an accessory pigment has been discovered.
• The molecular formula of Chlorophyll F is C₅₅H₇₀O₆N₄Mg.

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Functions of Chlorophyll

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The following are some important functions of Chlorophyll:

Biosynthesis of the Sugar

Plants use Chlorophyll A and B to absorb the energy from the sun. Chlorophyll is present in the thylakoid membranes of chloroplasts. The process of photosynthesis takes place in chloroplasts.

• Thylakoids are tiny membrane sacs that are piled on top of one another.
• There are many other proteins embedded in these membranes, which are responsible for transferring energy through chlorophyll to ATP.
• The proteins not only transfer the energy but also channel the energy into the synthesis of sugars, this process is called a photosystem.
• This whole process is termed 'Photosynthesis'. Photosynthesis takes place in plants, algae, and many other living organisms. 
• These organisms use carbon dioxide (CO₂), water (H₂O), and sunshine to generate glucose.
• They can either use this glucose in the process of cellular respiration to generate ATP, or they can mix it with other molecules to be stored.

Production of Oxygen

The process of photosynthesis gives out oxygen as the byproduct. Plants can utilize this oxygen for cellular respiration, but they also expel surplus oxygen into the atmosphere.

• The oxygen is generated during the first stage of the light cycle of the photosynthesis process.
• Water molecules are divided by plants to create electrons, hydrogen ions, and diatomic oxygen.
• The electrons power the electron transport chain, which in turn powers ATP synthesis.
• The oxygen is dispersed into the atmosphere. All of the oxygen we breathe is created in this manner.

Production Of Oxygen

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Difference Between Chlorophyll and Chloroplast

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The following are the differences between Chlorophyll and Chloroplast

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Benefits of Chlorophyll

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Chlorophyll is not only important for plants, and photosynthetic organisms but also for the survival of life on the earth. The benefits of chlorophyll are mentioned as follows:

• Chlorophyll produces sugar using the ATP mechanism, which is powered by chlorophyll.
• Plants are the primary producers and supply the foundation of the food chain.
• All other creatures in the food chain rely on the sugars produced by plants to survive.
• Chlorophyll is responsible for the production of oxygen.
• While chlorophyll does not directly create oxygen.
• Chlorophyll along with other complex proteins is linked to the transfer of electrons to molecules like ATP and NADPH, which may hold energy in bonds.
• The necessity for electrons to drive this process leads water molecules to split, resulting in the formation of oxygen.
• This oxygen is discharged into the atmosphere, which is used by all living organisms for breathing. 

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Things to Remember

• Chlorophyll is a pigment that is found in all green plants as well as a few other species.
• It is essential for photosynthesis, which is the process of converting light energy into a chemical form.
• A long carbon-hydrogen side chain is attached to the ring, which is called a phytol chain.
• Chlorophyll A is mainly found in higher plants and green algae.
• It is the primary light-harvesting pigment found in all photosynthetic organisms.
• The molecular formula of Chlorophyll A is C₅₅H₇₂O₅N₄Mg.
• Chlorophyll B is also found in higher plants and green algae.
• It acts as a light-harvesting pigment, transmitting light excitation to chlorophyll A.
• In oxygenic photosynthetic organisms, chlorophyll b is the second most prevalent chlorophyll.
• Chlorophyll produces sugar using the ATP mechanism, which is powered by chlorophyll.
• Plants are the primary producers and supply the foundation of the food chain.
• All other creatures in the food chain rely on the sugars produced by plants to survive.