CHLOROPHYLL: CHARACTERISTICS, STRUCTURE, LOCATION, TYPES - BIOLOGY

The chlorophyll is a biological pigment, indicating that it is a molecule capable of absorbing light. This molecule absorbs the wavelength corresponding to the color violet, blue and red, and reflects the light of green color. Therefore, the presence of chlorophyll is responsible for the green color of plants.

Its structure consists of a porphyrin ring with a magnesium center and a hydrophobic tail, called phytol. It is necessary to highlight the structural similarity of chlorophyll with the hemoglobin molecule.

The chlorophyll molecule is responsible for the green color in plants. Source: pixabay.com

Chlorophyll is located in thylakoids, membranous structures found inside chloroplasts. Chloroplasts are abundant in the leaves and other structures of plants.

Chlorophyll's main function is to capture light that will be used to drive photosynthetic reactions. There are different types of chlorophyll - the most common is a - that differ slightly in their structure and their absorption peak, in order to increase the amount of sunlight absorbed.

Historical perspective

The study of the chlorophyll molecule dates back to 1818 when it was first described by researchers Pelletier and Caventou, who coined the name “chlorophyll”. Later, in 1838 the chemical studies of the molecule began.

In 1851 Verdeil proposed the structural similarities between chlorophyll and hemoglobin. At the time, this resemblance was exaggerated and it was assumed that an iron atom was also located in the center of the chlorophyll molecule. Later the presence of magnesium was confirmed as the central atom.

The various types of chlorophyll were discovered in 1882 by Borodin using evidence provided by the microscope.

Pigments

Chlorophyll observed under a microscope. Kristian Peters - Fabelfroh

What is light

A key point for photosynthetic living organisms to have the ability to use light energy is the absorption of it. The molecules that carry out this function are called pigments and are present in plants and algae.

To better understand these reactions it is necessary to know certain aspects related to the nature of light.

Light is defined as a type of electromagnetic radiation, a form of energy. This radiation is understood as a wave and as a particle. One of the characteristics of electromagnetic radiation is wavelength, expressed as the distance between two successive ridges.

The human eye can perceive the wavelength ranging from 400 to 710 nanometers (nm = 10 ^-9 m). Short wavelengths are associated with greater amounts of energy. Sunlight includes white light, which consists of all wavelengths in the visible portion.

Regarding the nature of the particle, physicists describe photons as discrete packets of energy. Each of these particles has a characteristic wavelength and energy level.

When a photon hits an object three things can happen: be absorbed, transmitted or reflected.

Why is chlorophyll green?

Plants are perceived as green because chlorophyll mainly absorbs the blue and red wavelengths and reflects green. Nefronus

Not all pigments behave in the same way. Light absorption is a phenomenon that can occur at different wavelengths, and each pigment has a particular absorption spectrum.

The absorbed wavelength will determine the color at which we will visualize the pigment. For example, if it absorbs light at all its lengths, we will see the pigment completely black. Those that do not absorb all the lengths, reflect the rest.

In the case of chlorophyll, it absorbs the wavelengths corresponding to the colors violet, blue and red, and reflects green light. This is the pigment that gives plants their characteristic green color.

Chlorophyll is not the only pigment in nature

Although chlorophyll is one of the best known pigments, there are other groups of biological pigments such as carotenoids, which have reddish or orange tones. Therefore, they absorb light at a different wavelength than chlorophyll, serving as an energy transfer screen to chlorophyll.

In addition, some carotenoids have photoprotective functions: they absorb and dissipate light energy that could damage chlorophyll; or react with oxygen and form oxidative molecules that could damage cell structures.

Characteristics and structure

Chlorophylls are biological pigments that are perceived as green to the human eye and that participate in photosynthesis. We find them in plants and other organisms with the ability to transform light energy into chemical energy.

Chemically chlorophylls are magnesium-porphyrins. These are quite similar to the hemoglobin molecule, responsible for the transport of oxygen in our blood. Both molecules differ only in the types and location of the substituent groups on the tetrapyrrolic ring.

The metal of the porphyrin ring in hemoglobin is iron, while in chlorophyll it is magnesium.

The chlorophyll side chain is naturally hydrophobic or apolar, and is composed of four isoprenoid units, called phytol. This is esterified to the propioic acid group in ring number four.

If the chlorophyll is subjected to a heat treatment the solution takes an acidic pH, leading to the elimination of the magnesium atom from the center of the ring. If the heating persists or the solution decreases its pH even more, the phytol will end up hydrolyzing.

Location

Chlorophyll is one of the most widely distributed natural pigments and is found in different lineages of photosynthetic life. In the structure of plants we find it mainly in the leaves and other green structures.

If we go to a microscopic view, chlorophyll is found inside cells, specifically in chloroplasts. In turn, inside the chloroplasts there are structures formed by double membranes called thylakoids, which contain chlorophyll inside - along with other amounts of lipids and proteins.

Thylakoids are structures that resemble several stacked discs or coins, and this very compact arrangement is absolutely necessary for the photosynthetic function of chlorophyll molecules.

In prokaryotic organisms that carry out photosynthesis, there are no chloroplasts. For this reason, the thylakoids containing photosynthetic pigments are observed as part of the cell membrane, isolated inside the cell cytoplasm, or they build a structure in the inner membrane - a pattern observed in cyanobacteria.

Types

Chlorophyll a

There are several types of chlorophylls, which differ slightly in molecular structure and their distribution in photosynthetic lineages. That is, some organisms contain certain types of chlorophyll and others do not.

The main type of chlorophyll is called chlorophyll a, and in the lineage of plants in the pigment charged directly in the photosynthetic process and transforms light energy into chemical.

Chlorophyll b

A second type of chlorophyll is b and is also present in plants. Structurally it differs from chlorophyll a because the latter has a methyl group at carbon 3 of ring number II, and type b contains a formyl group in that position.

It is considered an accessory pigment and thanks to structural differences they have a slightly different absorption spectrum than variant a. As a result of this characteristic they differ in their color: chlorophyll a is blue-green and b is yellow-green.

The idea of these differential spectra is that both molecules complement each other in the absorption of light and manage to increase the amount of light energy that enters the photosynthetic system (so that the absorption spectrum is broadened).

Chlorophyll c and d

Chlorophyll d

There is a third type of chlorophyll, c, which we find in brown algae, diatoms, and dinoflagellates. In the case of cyanophyte algae, they only exhibit type a chlorophyll. Lastly, chlorophyll d is found in some protist organisms and also in cyanobacteria.

Chlorophyll in bacteria

There are a number of bacteria with the ability to photosynthesize. In these organisms there are chlorophylls known together as bacteriochlorophylls, and like the chlorophylls of eukaryotes, they are classified following the letters: a, b, c, d, e and g.

Historically, the idea was used that the chlorophyll molecule appeared first in the course of evolution. Today, thanks to sequence analysis, it has been proposed that probably the ancestral chlorophyll molecule was similar to a bacteriochlorophyll.

Features

The chlorophyll molecule is a crucial element in photosynthetic organisms, since it is responsible for the absorption of light.

In the machinery necessary to carry out photosynthesis there is a component called the photosystem. There are two and each one is made up of an "antenna" in charge of collecting the light and a reaction center, where we find type a chlorophyll.

Photosystems differ mainly in the absorption peak of the chlorophyll molecule: photosystem I has a peak at 700 nm, and II at 680 nm.

In this way, chlorophyll manages to fulfill its role in capturing light, which thanks to a complex enzymatic battery will be transformed into chemical energy stored in molecules such as carbohydrates.

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CHLOROPHYLL: CHARACTERISTICS, STRUCTURE, LOCATION, TYPES - BIOLOGY - 2025