welcome to solsarin . perhaps you have wondered why plants are green and ”what is the green pigment in plants called?” . on this post you find all the answers you need.
chlorophyll, any member of the most important class of pigments involved in photosynthesis, the process by which light energy is converted to chemical energy through the synthesis of organic compounds. Chlorophyll is found in virtually all photosynthetic organisms, including green plants, cyanobacteria, and algae. It absorbs energy from light; this energy is then used to convert carbon dioxide to carbohydrates.
Chlorophyll occurs in several distinct forms:
chlorophylls a and b are the major types found in higher plants and green algae; chlorophylls c and d are found, often with a, in different algae; chlorophyll e is a rare type found in some golden algae; and bacterio-chlorophyll occurs in certain bacteria.
In green plants chlorophyll occurs in membranous disk like units (thylakoids) in organelles called chloroplasts.
The chlorophyll molecule consists of a central magnesium atom surrounded by a nitrogen-containing structure called a porphyrin ring; attached to the ring is a long carbon–hydrogen side chain, known as a phytol chain. Variations are due to minor modifications of certain side groups. Chlorophyll is remarkably similar in structure to hemoglobin, the oxygen-carrying pigment found in the red blood cells of mammals and other vertebrates.
How chlorophyl works
Chlorophyll is a green compound found in leaves and green stems of plants. Initially, it was assumed that chlorophyll was a single compound but in 1864 Stokes showed by spectroscopy that chlorophyll was a mixture. If dried leaves are powdered and digested with ethanol, after concentration of the solvent, ‘crystalline’ chlorophyll is obtained, but if ether or aqueous acetone is used instead of ethanol, the product is ‘amorphous’ chlorophyll.
In 1912, Willstatter et al. (1) showed that chlorophyll was a mixture of two compounds, chlorophyll-a and chlorophyl
The two components were separated by shaking a light petroleum solution of chlorophyll with aqueous methanol: chlorophyll-a remains in the light petroleum but chlorophyll-b is transferred into the aqueous methanol. Cholorophyll-a is a bluish-black solid and cholorophyll-b is a dark green solid, both giving a green solution in organic solutions. In natural chlorophyll there is a ratio of 3 to 1 (of a to b) of the two components.
The intense green colour of chlorophyll is due to its strong absorbencies in the red and blue regions of the spectrum, shown in fig. 1. (2) Because of these absorbencies the light it reflects and transmits appears green.
Due to the green colour of chlorophyll, it has many uses as dyes and pigments. It is used in colouring soaps, oils, waxes and confectionary.
Chlorophyll’s most important use, however, is in nature, in photosynthesis. It is capable of channelling the energy of sunlight into chemical energy through the process of photosynthesis. In this process the energy absorbed by chlorophyll transforms carbon dioxide and water into carbohydrates and oxygen:
CO2 + H2O (CH2O) + O2
Note: CH2O is the empirical formula of carbohydrates.
The chemical energy stored by photosynthesis in carbohydrates drives biochemical reactions in nearly all living organisms.
In the photosynthetic reaction electrons are transferred from water to carbon dioxide, that is carbon dioxide is reduced by water.
Chlorophyll assists this transfer as when chlorophyll absorbs light energy, an electron in chlorophyll is excited from a lower energy state to a higher energy state. In this higher energy state, this electron is more readily transferred to another molecule.
This starts a chain of electron-transfer steps, which ends with an electron being transferred to carbon dioxide. Meanwhile, the chlorophyll which gave up an electron can accept an electron from another molecule. This is the end of a process which starts with the removal of an electron from water. Thus, chlorophyll is at the centre of the photosynthetic oxidation-reduction reaction between carbon dioxide and water.
Photosystems are the functional units for photosynthesis, defined by a particular pigment organization and association patterns, whose work is the absorption and transfer of light energy, which implies transfer of electrons.
Physically, photosystems are found in the thylakoid membranes. There are two kinds of photosystems: photosystem I (PSI) and photosystem II (PSII) (Fig. 3.3). PSII acts first during the light transformation process in photosynthesis, but it was named PSII because it was discovered second.
Each photosystem consists of two closely linked components: the first is the antenna complex formed by hundreds of pigment molecules that capture photons and transfer the harvested light energy to the second component named the reaction center, which possesses Chl a molecules in a matrix of protein. When excitation energy reaches chlorophyll a at the reaction center, electron transfer is initiated through an electron transport chain.
PSI is located at the outer surface of the thylakoid membrane, and contains chlorophyll b; chlorophyll a (in the forms: a-670, a-680, a-695, a-700), and carotenoids; and one particular chlorophyll a-700 form (named Chl a-P700) is the active reaction center. PSII is located at the inner surface of the thylakoid membrane, and contains chlorophyll b; chlorophyll a (forms a-660, a-670, a-680, a-695, a-700), phycobillins, and xanthophylls; and a Chl a-P680 form is the active reaction center.
In particular, organelles called chloroplasts allow plants to capture the energy of the Sun in energy-rich molecules; cell walls allow plants to have rigid structures as varied as wood trunks and supple leaves; and vacuoles allow plant cells to change size.
What Is the Origin of Chloroplasts?
Like mitochondria, chloroplasts likely originated from an ancient symbiosis, in this case when a nucleated cell engulfed a photosynthetic prokaryote. Indeed, chloroplasts resemble modern cyanobacteria, which remain similar to the cyanobacteria of 3 million years ago. However, the evolution of photosynthesis goes back even further, to the earliest cells that evolved the ability to capture light energy and use it to produce energy-rich molecules. When these organisms developed the ability to split water molecules and use the electrons from these molecules, photosynthetic cells started generating oxygen — an event that had dramatic consequences for the evolution of all living things on Earth
Today, chloroplasts retain small, circular genomes that resemble those of cyanobacteria, although they are much smaller. (Mitochondrial genomes are even smaller than the genomes of chloroplasts.) Coding sequences for the majority of chloroplast proteins have been lost, so these proteins are now encoded by the nuclear genome, synthesized in the cytoplasm, and transported from the cytoplasm into the chloroplast.
What Is the Function of Chloroplast Membranes?
Like mitochondria, chloroplasts are surrounded by two membranes. The outer membrane is permeable to small organic molecules, whereas the inner membrane is less permeable and studded with transport proteins. The innermost matrix of chloroplasts, called the stroma, contains metabolic enzymes and multiple copies of the chloroplast genome.
Chloroplasts also have a third internal membrane called the thylakoid membrane, which is extensively folded and appears as stacks of flattened disks in electron micrographs. The thylakoids contain the light-harvesting complex, including pigments such as chlorophyll, as well as the electron transport chains used in photosynthesis .
Importance of chlorophyll
Chlorophyll is the green pigment found in plants that allows them to convert sunlight into usable energy through a process called photosynthesis. More specifically, chlorophyll molecules are described as photoreceptors due to their light absorption properties.
There are two main types of chlorophyll, named chlorophyll a and chlorophyll b. These two different chlorophyll molecules are characterized by their varying chemical structure and specific infrared light that they absorb.
Chlorophyll a is the most commonly used photosynthetic pigment and absorbs blue, red and violet wavelengths in the visible spectrum.
It participates mainly in oxygenic photosynthesis in which oxygen is the main by-product of the process.
All oxygenic photosynthetic organisms contain this type of chlorophyll and include almost all plants and most bacteria.
Chlorophyll b primarily absorbs blue light and is used to complement the absorption spectrum of chlorophyll a by extending the range of light wavelengths a photosynthetic organism is able to absorb. Both of these types of chlorophyll work in concert to allow maximum absorption of light in the blue to red spectrum; however, not all photosynthetic organisms have the chlorophyll b pigment.
Role in Photosynthesis
Both of these chlorophyll molecules capture light energy and transfer it to the reaction center of the cell. From here, electrons are passed from this absorbed light energy to water molecules resulting in the formation of hydrogen ions and oxygen.
The oxygen is released as a by-product; whereas the hydrogen ions are transferred across the plant’s thylakoid membrane resulting in the phosphorylation of adenosine diphosphate (ADP) into adenosine triphosphate (ATP). ATP then subsequently reduces a coenzyme called nicotinamide adenine dinucleotide phosphate (NADP) to NADPH2, which is then used to convert carbon dioxide into a sugar.