Subjects: Science and technology — Life Sciences. View all related items in Oxford Reference ». Search for: 'photosynthetic pigments' in Oxford Reference ». All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single entry from a reference work in OR for personal use for details see Privacy Policy and Legal Notice. Oxford Reference. Publications Pages Publications Pages. For example, the photosynthetic protists called dinoflagellates, which are responsible for the "red tides" that often prompt warnings against eating shellfish, contain a variety of light-sensitive pigments, including both chlorophyll and the red pigments responsible for their dramatic coloration.
Figure 4: Diagram of a chloroplast inside a cell, showing thylakoid stacks Shown here is a chloroplast inside a cell, with the outer membrane OE and inner membrane IE labeled. Other features of the cell include the nucleus N , mitochondrion M , and plasma membrane PM. At right and below are microscopic images of thylakoid stacks called grana. Note the relationship between the granal and stromal membranes. Protein import into chloroplasts. Nature Reviews Molecular Cell Biology 5, doi Figure Detail.
Photosynthesis consists of both light-dependent reactions and light-independent reactions. In plants, the so-called "light" reactions occur within the chloroplast thylakoids, where the aforementioned chlorophyll pigments reside. When light energy reaches the pigment molecules, it energizes the electrons within them, and these electrons are shunted to an electron transport chain in the thylakoid membrane.
Meanwhile, each chlorophyll molecule replaces its lost electron with an electron from water; this process essentially splits water molecules to produce oxygen Figure 5. Figure 5: The light and dark reactions in the chloroplast The chloroplast is involved in both stages of photosynthesis.
The light reactions take place in the thylakoid. There, water H 2 O is oxidized, and oxygen O 2 is released. The dark reactions then occur outside the thylakoid. The products of this reaction are sugar molecules and various other organic molecules necessary for cell function and metabolism. Note that the dark reaction takes place in the stroma the aqueous fluid surrounding the stacks of thylakoids and in the cytoplasm.
The thylakoids, intake of water H 2 O , and release of oxygen O 2 occur on the yellow side of the cell to indicate that these are involved in the light reactions. The carbon fixation reactions, which involve the intake of carbon dioxide CO 2 , NADPH, and ATP, and the production of sugars, fatty acids, and amino acids, occur on the blue side of the cell to indicate that these are dark reactions.
An arrow shows the movement of a water molecule from the outside to the thylakoid stack on the inside of the chloroplast. Another arrow shows light energy from the sun entering the chloroplast and reaching the thylakoid stack.
An arrow shows the release of an oxygen molecule O 2 from the thylakoid stack to the outside of the chloroplast. Once the light reactions have occurred, the light-independent or "dark" reactions take place in the chloroplast stroma.
During this process, also known as carbon fixation, energy from the ATP and NADPH molecules generated by the light reactions drives a chemical pathway that uses the carbon in carbon dioxide from the atmosphere to build a three-carbon sugar called glyceraldehydephosphate G3P.
Cells then use G3P to build a wide variety of other sugars such as glucose and organic molecules. Many of these interconversions occur outside the chloroplast, following the transport of G3P from the stroma.
The products of these reactions are then transported to other parts of the cell, including the mitochondria, where they are broken down to make more energy carrier molecules to satisfy the metabolic demands of the cell. In plants, some sugar molecules are stored as sucrose or starch. This page appears in the following eBook. Aa Aa Aa. Photosynthetic Cells.
What Is Photosynthesis? Why Is it Important? Figure 2. Figure 3: Structure of a chloroplast. Figure 4: Diagram of a chloroplast inside a cell, showing thylakoid stacks.
Shown here is a chloroplast inside a cell, with the outer membrane OE and inner membrane IE labeled. However, none of these should be considered a photosynthetic pigment. Photosynthetic pigments are the only pigments that have the ability to absorb energy from sunlight and make it available to the photosynthetic apparatus. In land plants, there are two classes of these photosynthetic pigments, the chlorophylls and the carotenoids. There are different classes of chlorophylls, major of them are chlorophyll-a chl-a and chlorophyll-b chl-b.
In plants, the ratio chl-a to chl-b is about three to one. Only chl-a is a constituent of the photosynthetic reaction centers and so it can be regarded as the central photosynthesis pigment.
Also, the light energy absorbed by chl-b can be transferred very efficiently to chl-a. The basic structure of chlorophyll has tadpole like head with Mg- tetra pyrrole ring and phytol tail. The porphyrin head is hydrophilic which consists of 4 pyrrole rings joined by CH bridges. A long lipophilic phytol tail of a long branched hydrocarbon chain with one C-C double bond is attached to the ring at C-7 position of 4th pyrrole.
Fig: Molecular structure of Chlorophyll-a and Chlorophyll-b The structure of chlorophylls has remained remarkably constant during the course of evolution. Purple bacteria, probably formed more than 3 billion years ago, contain as photosynthetic pigment a bacteriochlorophyll- a, which differs from the chlorophyll-a only by the alteration of one side chain and by the lack of one double bond.
Chlorophyll molecules are bound to chlorophyll-binding proteins. This binding may cause difference the absorption spectrum of the bound chlorophyll from the absorption spectrum of the free chlorophyll.
0コメント