Light-Independent Reaction

12 Key excerpts on "Light-Independent Reaction"

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  Concepts of Biology

  • Samantha Fowler, Rebecca Roush, James Wise(Authors)
  • 2016(Publication Date)
  • Openstax

    (Publisher)

  The Interworkings of the Calvin Cycle In plants, carbon dioxide (CO 2 ) enters the chloroplast through the stomata and diffuses into the stroma of the chloroplast—the site of the Calvin cycle reactions where sugar is synthesized. The reactions are named after the scientist who discovered them, and reference the fact that the reactions function as a cycle. Others call it the Calvin-Benson cycle to include the name of another scientist involved in its discovery (Figure 5.14). Figure 5.14 Light-dependent reactions harness energy from the sun to produce ATP and NADPH. These energy- carrying molecules travel into the stroma where the Calvin cycle reactions take place. The Calvin cycle reactions (Figure 5.15) can be organized into three basic stages: fixation, reduction, and regeneration. In the stroma, in addition to CO 2 , two other chemicals are present to initiate the Calvin cycle: an enzyme abbreviated RuBisCO, and the molecule ribulose bisphosphate (RuBP). RuBP has five atoms of carbon and a phosphate group on each end. RuBisCO catalyzes a reaction between CO 2 and RuBP, which forms a six-carbon compound that is immediately converted into two three-carbon compounds. This process is called carbon fixation, because CO 2 is “fixed” from its inorganic form into organic molecules. ATP and NADPH use their stored energy to convert the three-carbon compound, 3-PGA, into another three-carbon compound called G3P. This type of reaction is called a reduction reaction, because it involves the gain of electrons. A reduction is the gain of an electron by an atom or molecule. The molecules of ADP and NAD + , resulting from the reduction reaction, return to the light-dependent reactions to be re-energized. One of the G3P molecules leaves the Calvin cycle to contribute to the formation of the carbohydrate molecule, which is commonly glucose (C 6 H 12 O 6 ).

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  Plant Biochemistry

  • Hans-Walter Heldt, Birgit Piechulla(Authors)
  • 2010(Publication Date)
  • Academic Press

    (Publisher)

  The reaction chain for the formation of triose phosphate from CO 2, ATP, and NADPH was formerly called the dark reaction of photosynthesis, as it requires no light per se and theoretically it should also be able to proceed in the dark. The fact is, however, that in leaves this reaction does not proceed during darkness, since some of the enzymes of the reaction chain, due to regulatory processes, are active only during illumination (section 6.6). Figure 6.1 Schematic presentation of photosynthesis in a chloroplast. Figure 6.2 Overall reaction of photosynthetic CO 2 fixation. Between 1946 and 1953 Melvin Calvin and his collaborators Andrew Benson and James Bassham, in Berkeley, California, resolved the mechanism of photosynthetic CO 2 assimilation. In 1961 Calvin was awarded the Nobel Prize in Chemistry for this fundamental discovery. A prerequisite for the elucidation of the CO 2 fixation pathway was the discovery of the radioactive carbon isotope 14 C in 1940, which, as a by-product of nuclear reactors, was available in larger amounts in the United States after 1945. Calvin chose the green alga Chlorella for his investigations. He added radioactively labeled CO 2 to illuminated algal suspensions, killed the algae after a short incubation period by adding hot ethanol, and used paper chromatography to analyze the radioactively labeled products of the CO 2 fixation. By successively shortening the incubation time, he was able to show that 3-phosphoglycerate was synthesized as the first stable product of CO 2 fixation. More detailed studies revealed that CO 2 fixation proceeds by a cyclic process, which has been named the Calvin cycle after its discoverer. Reductive pentose phosphate pathway is another term that will be used in some sections of this book

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  Cambridge O Level Biology 5090

  • Azhar ul Haque Sario(Author)
  • 2023(Publication Date)
  • tredition

    (Publisher)

  Photosynthesis is vital for life on Earth. It is the primary process by which energy enters the biosphere. Plants use this process to produce glucose, which serves as a fundamental energy source for many organisms, including humans. Additionally, photosynthesis is responsible for producing the majority of the oxygen in the Earth's atmosphere, which is crucial for the survival of aerobic organisms.

  Light-Dependent Reactions: These reactions occur in the thylakoid membranes of chloroplasts. They involve the absorption of light by chlorophyll and other pigments, which drives the synthesis of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). Water molecules are split in this process, releasing oxygen as a by-product. Light-Independent Reactions (Calvin Cycle): These reactions take place in the stroma of chloroplasts. They use the ATP and NADPH produced in the lightdependent reactions to convert carbon dioxide into glucose. This process does not require light directly but depends on the products of the light-dependent reactions.

  2. Factors Affecting Photosynthesis Several factors influence the rate of photosynthesis: Light Intensity: Increased light intensity boosts the rate of photosynthesis, up to a certain point.

  Carbon Dioxide Concentration: Higher levels of CO2 can enhance photosynthesis until the process reaches a saturation point.

  Temperature: Photosynthesis has an optimal temperature range. Deviations from this range can slow down the process. Water Availability: Adequate water supply is crucial for photosynthesis, especially for the stability of the plant and the efficiency of enzymatic reactions. 3. Implications in Biology and Ecology Photosynthesis is not just a biochemical process; it has profound implications in various fields:

  Ecology: It forms the basis of most food chains and food webs, determining the energy flow in ecosystems. Agriculture: Understanding photosynthesis aids in enhancing crop yields and managing agricultural ecosystems.

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  Biochemistry

  • Donald Voet, Judith G. Voet(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  21 Photosynthesis: Bioinorganic Chemistry and Physiology

  1 Chloroplasts

  2 Light Reactions

  A. Absorption of Light

  B. Electron Transport in Purple Photosynthetic Bacteria

  C. Two-Center Electron Transport

  D. Photophosphorylation

  3 Dark Reactions

  A. The Calvin Cycle

  B. Control of the Calvin Cycle

  C. Photorespiration and the C4 Cycle

  Life on Earth depends on the sun. Plants and cyanobacteria chemically sequester light energy through photosynthesis, a light-driven process in which CO2 is “fixed” to yield carbohydrates (CH2 O).

  This process, in which CO2 is reduced and H2 O is oxidized to yield carbohydrates and O2 , is essentially the reverse of oxidative carbohydrate metabolism. ­Photosynthetically produced carbohydrates therefore serve as an energy source for the organism that produced them as well as for nonphotosynthetic organisms that directly or indirectly consume photosynthetic organisms. In fact, even modern industry is highly dependent on the products of photosynthesis because coal, oil, and gas (the so-called fossil fuels) are thought to be the remains of ancient organisms. It is estimated that photosynthesis annually fixes ∼1011 tons of carbon, which represents the storage of over 1018 kJ of energy. Moreover, photosynthesis, over the eons, has produced the O2 in Earth's atmosphere (Section 1-1C ).

  The notion that plants obtain nourishment from such insubstantial things as light and air took nearly two centuries to develop. In 1648, the Flemish physician Jean Baptiste van Helmont reported that growing a potted willow tree from a shoot caused an insignificant change in the weight of the soil in which the tree had been rooted. Although another century was to pass before the law of conservation of matter was formulated, van Helmont attributed the tree's weight gain to the water it had taken up. This idea was extended in 1727 by Stephen Hales, who proposed that plants extract some of their matter from the air.

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  Postharvest Physiology and Biochemistry of Fruits and Vegetables

  • Elhadi M. Yahia, Armando Carrillo-Lopez(Authors)
  • 2018(Publication Date)
  • Woodhead Publishing

    (Publisher)

  In this reaction, the NADPH and ATP previously produced in the light-dependent reaction are used for the fixation of CO 2 into carbohydrates. An enzyme (ribulose bisphosphate carboxylase-oxygenase) is responsible for carbon dioxide fixation, in a metabolic reaction known as the Calvin cycle. These reactions occur when light reaches the leaf, and stomata are open, allowing the entry of CO 2 to photosynthetic cells. Each requirement for plant growth and development depends on the internal energy balance, which is the result of carbon assimilation in photosynthesis. Carbohydrates derived from photosynthesis are the energy source for plant maintenance (using glucose for the cell respiration process) in the first instance, and then to support metabolic energy needs for growth, when structural carbohydrates like cellulose are also required. Consequently, dry matter is accumulated which is subsequently distributed internally in the plant for the development of new structures such as branches, wood, flowers, and fruits. In this way, dry matter (storage assimilates) and carbon flow derived from photosynthesis are allocated during fruit growth and development. Therefore, fruit development, maturation, ripening, and quality are influenced by the process of photosynthetic activity, which is the reason for the great importance of this process (photosynthesis), not only during the development of horticultural commodities (fruits, vegetables, flowers), but also its consequences during postharvest

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  Structure and Function of Plants

  • Jennifer W. MacAdam(Author)
  • 2011(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Figure 10.6 ). During the light reactions of photosynthesis, both ATP and NADPH accumulate in the stroma, where they can be used in the synthesis of carbohydrates. These reactions are called the “light” or photochemical reactions of photosynthesis because they utilize light energy to create the chemical energy of ATP and NADPH, and therefore only take place in the light.

  The “dark” reactions of photosynthesis

  As long ago as 1905, it was determined that in dim light, altering the temperature at which photosynthesis was occurring did not affect the rate of photosynthesis, but increasing the light intensity did. However, in bright light, the rate of photosynthesis was affected by change in temperature, while a further increase in light had no effect. The rate of biochemical reactions of living organisms increases with increasing temperature within the temperature range at which the organism thrives. Investigation of these differences led to the early understanding of photosynthesis as a group of photochemical (“light”) reactions linked through ATP and NADPH to a group of biochemical (“dark”) reactions. In dim light, photosynthetic rate is limited by the photochemical (or light) reactions in which the energy of light is captured and converted to ATP and NADPH. However, in bright light, the rate of the light reactions is high, but photosynthesis can be limited by the rate of the associated biochemical (or dark) reactions that use the energy created in the light reactions to make carbohydrates.

  In reality, both the light and dark reactions of photosynthesis occur only in the light. The biochemical reactions are termed the dark reactions simply to indicate that light intensity is not a direct regulatory factor. In the dark, when the flow of chemical energy from the light reactions has stopped, then the dark reactions stop for lack of ATP and NADPH.

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  Light

  Physical and Biological Action

  • Howard H. Seliger, William D. McElroy(Authors)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  In making use of the free energy of sunlight, the green plant is able to fix carbon dioxide and split water to evolve oxygen. Through a series of reactions which are reasonably well known, carbohydrates and other molecules are synthesized. Thus light energy serves indirectly as a source of free energy for all living things. The immediate end products of metabolism are carbon dioxide and water. Consequently the combination of photosynthetic organisms and heterotrophic organisms gives us a biological machine which continually turns over C0 2 and H 2 0 on the surface of the earth. It has been calcu-lated that each carbon dioxide molecule in the atmosphere is fixed and incorporated into some plant structure once in every 200 years and that all the oxygen is renewed by plants every 2000 years. During the past 15 years considerable progress has been made in understanding the proc-esses involved in carbon dioxide reduction and fixation in green plants as well as the primary photochemical events. It is not possible for us to review all of the pertinent data concerning the physiological, biophysical, and biochemical investigations on photosynthesis, and consequently the reader is referred to the extensive reviews and monographs: Rabinowitch (1945, 1951, 1956), Bassham (1963), Gaffron (1960), Jagendorf (1962), Whatley and Losada (1964), Clayton (1964) and Blinks (1964). Photosynthesis in green plants occurs in the chloroplast which consists of a lamellar phase imbedded in a matrix (see Fig. 5.9), surrounded by a membrane. The lamellar structures can be separated from the matrix and recent Studies by Park and Pon (1961, 1962), Lichtenthaler and Park (1963) and Park and Biggins (1964) indicate that it is made up of subunits which Calvin (1962) has called quantasomes. Aggregates of 6 to 7 quantasomes are capable of performing the light reactions and the asso-ciated electron transport processes of photosynthesis. Recently, Lieh-

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  Plant Cell Biology

  • (Author)
  • 2014(Publication Date)
  • White Word Publications

    (Publisher)

  The oxidation of water is catalyzed in photosystem II by a redox-active structure that contains four manganese ions and a calcium ion; this oxygen-evolving complex binds two water molecules and stores the four oxidizing equivalents that are required to drive the water-oxidizing reaction. Photosystem II is the only known biological enzyme that carries out this oxidation of water. The hydrogen ions contribute to the transmembrane chemiosmotic potential that leads to ATP synthesis. Oxygen is a waste product of light-dependent reactions, but the majority of organisms on Earth use oxygen for cellular respiration, including photosynthetic organisms. Light-Independent Reactions The Calvin Cycle In the Light-independent or dark reactions the enzyme RuBisCO captures CO 2 from the atmosphere and in a process that requires the newly formed NADPH, called the Calvin-Benson Cycle, releases three-carbon sugars, which are later combined to form sucrose and starch. The overall equation for the Light-Independent Reactions in green plants is: ________________________ WORLD TECHNOLOGIES ________________________ 3 CO 2 + 9 ATP + 6 NADPH + 6 H + → C 3 H 6 O 3 -phosphate + 9 ADP + 8 P i + 6 NADP + + 3 H 2 O Overview of the Calvin cycle and carbon fixation To be more specific, carbon fixation produces an intermediate product, which is then converted to the final carbohydrate products. The carbon skeletons produced by photosynthesis are then variously used to form other organic compounds, such as the building material cellulose, as precursors for lipid and amino acid biosynthesis, or as a fuel in cellular respiration. The latter occurs not only in plants but also in animals when the energy from plants gets passed through a food chain.

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  Photosynthesis

  Solar Energy for Life

  • Dmitry Shevela, Lars Olof Björn, Govindjee(Authors)
  • 2018(Publication Date)
  • WSPC

    (Publisher)

  Chapter 3

  Basics of Photosynthesis: Light-Dependent Reactions

  3.1Overview: Harvesting Sunlight to Drive Redox Chemistry

  In all photosynthetic organisms (both oxygenic and anoxygenic) the photosynthetic light reactions begin with the absorption of light (photons) by pigments in light-harvesting complexes, embedded in the thylakoid membrane (or in case of cyanobacteria, also in phycobilisomes). The antenna (both outer and inner) systems deliver the energy of absorbed light (excitation energy; we shall discuss it in Section 3.2 ) to pigment–protein reaction center complexes, Photosystems II and I (PSII and PSI; see Section 3.3 ), both embedded in the thylakoid membrane (Fig. 3.1 ). As a consequence of primary photochemistry, which takes place after trapping of the excitation energy by special photoactive chlorophyll (Chl) molecules in the reaction centers of the two photosystems, light energy is converted into chemical energy. This energy drives the redox chemistry of the stepwise linear electron “transfer” from water to the oxidized form of nicotinamide adenine dinucleotide phosphate (NADP+ ), involving PSII and PSI as well as the Cyt

  b6 f

  complex (Fig. 3.1 ). In this chapter we shall also briefly describe photosynthetic ATP production by ATP synthase from ADP and inorganic phosphate (see Section 3.3.3 ).

  3.2Capturing the Energy of Light

  The first step in photosynthesis is the absorption of light by pigment molecules which include Chl

  a

  , other Chls, or phycobilins, or fucoxanthol, depending on the organism; this step occurs within femtoseconds (one femtosecond is 10−15 s; there are as many femtoseconds in a second as there are seconds in 31.54 million years!). This event means that a photon disappears, and the energy of the molecule increases, the pigment molecule is in an excited state. We need to consider only two kinds of energy of the molecule here: the electronic energy and the vibrational energy, and both are changed when the photon is absorbed, as a consequence of the so-called

  Franck-Condon principle

  : Upon absorption of a photon, the electronic transition from the ground state to the excited state occurs without a change in the position of the nuclei, because “the electrons are light and the nuclei are heavy,” and the molecule goes to a higher vibrational state (see Fig. 3.2 , and the discussion that follows; for Franck-Condon principle, see Rabinowitch and Govindjee [1969], and Atkins and Friedman [1999]). In addition, we have “vibronic” energy, which is a combination of “vibrational” and “electronic” energy: the “vibronic energy coupling” refers to the interaction between electronic and nuclear vibrational energy. This interaction, indeed, makes the light harvesting more efficient in several cases [Dean

  et al.

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  The Science of Grapevines

  • Markus Keller(Author)
  • 2020(Publication Date)
  • Academic Press

    (Publisher)

  It is achieved by the action of 13 enzyme proteins in the Calvin cycle located in the chloroplast stroma. The Calvin cycle is named after one of its discoverers, the American biochemist Melvin Calvin, but is also called the photosynthetic carbon reduction cycle or the reductive pentose phosphate pathway. The cycle proceeds in three successive stages (Fig. 4.4). The first stage is termed carboxylation and combines CO 2 and protons derived from water with ribulose-1,5-bisphosphate, a molecule that specializes as a carbon acceptor, to generate two intermediate molecules of 3-phosphoglycerate, thereby converting the inorganic CO 2 into an organic molecule. As its name suggests, this initial organic compound, like all other intermediates of the Calvin cycle, is a sugar phosphate. Despite the simplified and convenient equation introduced above, glucose is not a direct product of the Calvin cycle. Because 3-phosphoglycerate is the first stable product of CO 2 fixation and contains three carbon atoms, grapevines are grouped with most other crop plants as the so-called C 3 plants. Fig. 4.4 The three stages of the Calvin cycle that converts CO 2 into carbohydrates. Illustration by M. Keller. The carboxylation step is catalyzed by the enzyme ribulose bisphosphate carboxylase/oxygenase (or rubisco for short). Owing to its importance in carbon assimilation, rubisco occurs in chloroplasts at very high concentration—often in substantial excess. It represents approximately one-third of a leaf's total protein complement, appropriating up to half of the leaf's nitrogen, which arguably makes it the most abundant protein nature ever invented (Spreitzer and Salvucci, 2002). Rubisco commandeers an extremely prominent position in grapevine physiology because almost all the carbon that is assimilated is initially “captured” by this protein. As its full name suggests, the enzyme “works” in two opposing directions so that CO 2 competes with oxygen for the same molecular acceptor

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  Plant Biochemistry

  • P. M. Dey, J. B. Harborne(Authors)
  • 1997(Publication Date)
  • Academic Press

    (Publisher)

  2

  Photosynthesis

  J.R. Bowyer and R.C. Leegood

  2.1 Introduction 2.2 Light energy utilization to produce ATP and NADPH 2.3 The Benson-Calvin cycle 2.4 Photorespiration

  2.5 C4 photosynthesis

  2.6 Crassulacean Acid Metabolism Acknowledgements Background reading Further reading Other references

  2.1 INTRODUCTION

  Photosynthesis is the process by which organisms convert light energy into chemical energy in the form of reducing power (as NADPH or NADH) and ATP, and use these chemicals to drive carbon dioxide fixation and reduction to produce sugars. In oxygenic photosynthetic organisms, including higher plants, the source of reducing equivalents is H2 O, releasing O2 as a by-product. The overall reaction of oxygenic photosynthesis can be represented as:

  CO2 + 2H2 O → (CH2 O) + H2 O + O2

  This process is responsible for producing virtually all the O2 in the atmosphere and for fixing about 1011 tons of carbon from CO2 into organic compounds annually.

  The sugars produced by the photosynthetic fixation of CO2 provide raw material for the biosynthesis of all the organic molecules found in plants. They are also the source of the chemical fuel which is oxidized by oxygen in the mitochondria in order to generate ATP for use in a wide variety of energy-consuming processes in the plant such as biosynthesis, active transport of ions and metabolites across membranes, and intracellular movement of organelles.

  In plants, photosynthesis occurs primarily in leaf cells in organelles called chloroplasts, which are about 5 μm long and bound by two membrane envelopes. The number of chloroplasts per leaf cell varies from 1 to over 100, depending on cell type, species and growth conditions.

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  Cellular Metabolism in Cell Biology

  • (Author)
  • 2014(Publication Date)
  • Research World

    (Publisher)

  During the second stage, the Light-Independent Reactions use these products to capture and reduce carbon dioxide. Most organisms that utilize photosynthesis to produce oxygen use visible light to do so, although at least three use infrared radiation. ________________________ WORLD TECHNOLOGIES ________________________ Photosynthetic membranes and organelles Chloroplast ultrastructure: 1. outer membrane 2. intermembrane space 3. inner membrane (1+2+3: envelope) 4. stroma (aqueous fluid) 5. thylakoid lumen (inside of thylakoid) 6. thylakoid membrane 7. granum (stack of thylakoids) 8. thylakoid (lamella) 9. starch 10. ribosome 11. plastidial DNA 12. plastoglobule (drop of lipids) The proteins that gather light for photosynthesis are embedded within cell membranes. The simplest way these are arranged is in photosynthetic bacteria, where these proteins are held within the plasma membrane. However, this membrane may be tightly folded into cylindrical sheets called thylakoids, or bunched up into round vesicles called intracytoplasmic membranes . These structures can fill most of the interior of a cell, giving the membrane a very large surface area and therefore increasing the amount of light that the bacteria can absorb. In plants and algae, photosynthesis takes place in organelles called chloroplasts. A typical plant cell contains about 10 to 100 chloroplasts. The chloroplast is enclosed by a membrane. This membrane is composed of a phospholipid inner membrane, a phospholipid outer membrane, and an intermembrane space between them. Within the membrane is an aqueous fluid called the stroma. The stroma contains stacks (grana) of thylakoids, which are the site of photosynthesis. The thylakoids are flattened disks, bounded by a membrane with a lumen or thylakoid space within it. The site of

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