Photosystems are protein complexes found in plant and bacterial membranes that carry out the light-dependent reactions of photosynthesis. They contain reaction centers that use light energy to drive electron transfer, as well as light-harvesting complexes that absorb light and transfer energy to the reaction centers. There are two types of reaction centers, Photosystem I and Photosystem II. In oxygenic photosynthesis, which occurs in plants, algae and cyanobacteria, both photosystems work together to drive electron transfer through an electron transport chain and produce ATP and NADPH, while also splitting water to produce oxygen.
B.Sc Micro II Microbial physiology Unit 2 Bacterial RespirationRai University
Respiration is the energy source to all living organism. Bacterial ETS system generates energy for bacteria in form of ATP using oxidative phosphorylation.
This document provides an overview of oxidative phosphorylation and electron transport chain in mitochondria. It discusses:
1) The chemiosmotic theory proposed by Peter Mitchell which explains how the transport of electrons through the respiratory chain is utilized to produce ATP from ADP and Pi. Proton pumping by Complexes I, III, and IV generates an electrochemical gradient used by ATP synthase.
2) The components of the electron transport chain, including NADH dehydrogenase, succinate dehydrogenase, ubiquinone, cytochromes, and oxygen, arranged in order of increasing redox potential.
3) The four complexes of the electron transport chain - Complexes I-IV - and their roles in proton pumping and
The document summarizes the three main stages of cellular respiration:
1. Glycolysis breaks down glucose into pyruvate and produces a small amount of ATP.
2. The citric acid cycle further breaks down pyruvate and produces more ATP and electron carriers.
3. During oxidative phosphorylation, electrons are passed through an electron transport chain which pumps protons across a membrane, building an electrochemical gradient. ATP synthase uses this gradient to produce the majority of ATP from cellular respiration.
The document summarizes oxidative phosphorylation, which is the process by which electrons from oxidation reactions are used to generate ATP from ADP and inorganic phosphate. It describes the electron transport chain and carriers that shuttle electrons between complexes. The energy from electron transport is used to pump protons across the inner mitochondrial membrane, creating an electrochemical gradient that drives ATP synthesis by ATP synthase. The chemiosmotic theory of how this proton gradient is harnessed for ATP production is also summarized.
Biological oxidation is the process by which organic substances like carbohydrates, fats, and proteins release energy through redox reactions in cells. This energy is captured in the form of ATP, which is used to power various cellular processes. The electron transport chain located in the inner mitochondrial membrane facilitates the transfer of electrons from electron carriers like NADH and FADH2 to oxygen. This releases energy to synthesize ATP through oxidative phosphorylation and substrate-level phosphorylation. Key components of the electron transport chain include complexes I-IV which contain enzymes, cofactors, and cytochromes that sequentially pass electrons from one to the next until they reach oxygen, the final electron acceptor.
1. Photosynthesis converts light energy from the sun into chemical energy through a series of reactions that take place in the chloroplasts of plants, algae, and some bacteria.
2. The light reactions use energy from sunlight to convert water and carbon dioxide into oxygen and energy carriers (ATP and NADPH). The Calvin cycle then uses this energy to convert the carbon from carbon dioxide into sugars.
3. Photosynthesis occurs in two stages - the light-dependent reactions that take place in the thylakoid membranes to produce ATP and NADPH, and the light-independent Calvin cycle that uses these products to fix carbon from carbon dioxide into organic compounds like glucose.
1. Biological oxidation is carried out by enzymes and involves the addition of oxygen, removal of hydrogen, or incorporation of oxygen into substrates. It is restricted to three main classes of reactions.
2. Enzymes responsible for biological oxidation include oxidases, oxygenases, hydroxyperoxidases, and dehydrogenases. Oxidases directly use oxygen as a hydrogen acceptor, while oxygenases incorporate oxygen into substrates.
3. The electron transport chain is the final common pathway for aerobically transferring electrons generated during substrate oxidation to oxygen. It involves electron carriers like cytochromes and the proton gradient generated powers ATP synthesis.
1) A protein coded for by a DNA clone from the duckweed Landoltia Punctata matched significantly to ferredoxin, an iron-sulfur protein involved in electron transport during photosynthesis.
2) Ferredoxin transports electrons from photosystem I to ferredoxin-NADP+-reductase (FNR), which reduces NADP+ to NADPH for use in the Calvin cycle to produce sugars.
3) The homology of ferredoxin's amino acid sequence between different plant species indicates its important role in stabilizing the iron-sulfur cluster and facilitating electron transport during photosynthesis.
B.Sc Micro II Microbial physiology Unit 2 Bacterial RespirationRai University
Respiration is the energy source to all living organism. Bacterial ETS system generates energy for bacteria in form of ATP using oxidative phosphorylation.
This document provides an overview of oxidative phosphorylation and electron transport chain in mitochondria. It discusses:
1) The chemiosmotic theory proposed by Peter Mitchell which explains how the transport of electrons through the respiratory chain is utilized to produce ATP from ADP and Pi. Proton pumping by Complexes I, III, and IV generates an electrochemical gradient used by ATP synthase.
2) The components of the electron transport chain, including NADH dehydrogenase, succinate dehydrogenase, ubiquinone, cytochromes, and oxygen, arranged in order of increasing redox potential.
3) The four complexes of the electron transport chain - Complexes I-IV - and their roles in proton pumping and
The document summarizes the three main stages of cellular respiration:
1. Glycolysis breaks down glucose into pyruvate and produces a small amount of ATP.
2. The citric acid cycle further breaks down pyruvate and produces more ATP and electron carriers.
3. During oxidative phosphorylation, electrons are passed through an electron transport chain which pumps protons across a membrane, building an electrochemical gradient. ATP synthase uses this gradient to produce the majority of ATP from cellular respiration.
The document summarizes oxidative phosphorylation, which is the process by which electrons from oxidation reactions are used to generate ATP from ADP and inorganic phosphate. It describes the electron transport chain and carriers that shuttle electrons between complexes. The energy from electron transport is used to pump protons across the inner mitochondrial membrane, creating an electrochemical gradient that drives ATP synthesis by ATP synthase. The chemiosmotic theory of how this proton gradient is harnessed for ATP production is also summarized.
Biological oxidation is the process by which organic substances like carbohydrates, fats, and proteins release energy through redox reactions in cells. This energy is captured in the form of ATP, which is used to power various cellular processes. The electron transport chain located in the inner mitochondrial membrane facilitates the transfer of electrons from electron carriers like NADH and FADH2 to oxygen. This releases energy to synthesize ATP through oxidative phosphorylation and substrate-level phosphorylation. Key components of the electron transport chain include complexes I-IV which contain enzymes, cofactors, and cytochromes that sequentially pass electrons from one to the next until they reach oxygen, the final electron acceptor.
1. Photosynthesis converts light energy from the sun into chemical energy through a series of reactions that take place in the chloroplasts of plants, algae, and some bacteria.
2. The light reactions use energy from sunlight to convert water and carbon dioxide into oxygen and energy carriers (ATP and NADPH). The Calvin cycle then uses this energy to convert the carbon from carbon dioxide into sugars.
3. Photosynthesis occurs in two stages - the light-dependent reactions that take place in the thylakoid membranes to produce ATP and NADPH, and the light-independent Calvin cycle that uses these products to fix carbon from carbon dioxide into organic compounds like glucose.
1. Biological oxidation is carried out by enzymes and involves the addition of oxygen, removal of hydrogen, or incorporation of oxygen into substrates. It is restricted to three main classes of reactions.
2. Enzymes responsible for biological oxidation include oxidases, oxygenases, hydroxyperoxidases, and dehydrogenases. Oxidases directly use oxygen as a hydrogen acceptor, while oxygenases incorporate oxygen into substrates.
3. The electron transport chain is the final common pathway for aerobically transferring electrons generated during substrate oxidation to oxygen. It involves electron carriers like cytochromes and the proton gradient generated powers ATP synthesis.
1) A protein coded for by a DNA clone from the duckweed Landoltia Punctata matched significantly to ferredoxin, an iron-sulfur protein involved in electron transport during photosynthesis.
2) Ferredoxin transports electrons from photosystem I to ferredoxin-NADP+-reductase (FNR), which reduces NADP+ to NADPH for use in the Calvin cycle to produce sugars.
3) The homology of ferredoxin's amino acid sequence between different plant species indicates its important role in stabilizing the iron-sulfur cluster and facilitating electron transport during photosynthesis.
The document summarizes key aspects of oxidative phosphorylation and ATP production in mitochondria. It describes how electrons from NADH and FADH2 are transferred through electron transport chain complexes I-IV, pumping protons out of the mitochondrial matrix. This generates a proton gradient that drives ATP synthase to phosphorylate ADP to ATP. The coupling of electron transport and ATP production via this proton gradient is explained by Mitchell's chemiosmotic theory.
The document summarizes cellular respiration and the production of ATP through oxidative phosphorylation. It discusses how carbohydrates, fats, and amino acids are broken down to feed into the electron transport chain, whose purpose is to release energy to drive the synthesis of ATP from ADP and inorganic phosphate. The process occurs within the inner mitochondrial membrane in complexes of the electron transport chain, and generates more ATP per pair of electrons carried through when NADH is oxidized compared to FADH2. The availability of ADP regulates the rate of ATP production. Oxygen consumption and ADP levels increase under conditions when ATP is needed at a rapid rate, such as during exercise. Some physiological and synthetic uncoupling agents can disrupt this phosphorylation process
This document contains multiple sections from lectures by Dr. Ashok Kumar J on the topic of cellular respiration and oxidative phosphorylation. It discusses key concepts such as oxidation, reduction, the electron transport chain, ATP synthase, the chemiosmotic theory proposed by Peter Mitchell, and disorders that can result from mitochondrial dysfunction.
Biological oxidation (part - III) Oxidative PhosphorylationAshok Katta
Biological oxidation (part - III) Oxidative Phosphorylation
- Mechanism of Oxidative Phosphorylation
-- Chemiosmotic theory
-P:O Ratio
Substrate Level Phosphorylation
Shuttle Systems for Oxidation of Extramitochondrial NADH
1) Oxidative phosphorylation uses electron transport chain complexes in the mitochondrial inner membrane to generate ATP from ADP and inorganic phosphate. As electrons are passed through Complexes I-IV, protons are pumped from the matrix to the intermembrane space, building an electrochemical gradient.
2) Protons flow back through ATP synthase, driving the phosphorylation of ADP to ATP in the matrix. The electron carriers, including ubiquinone and cytochrome c, shuttle electrons and protons between the complexes.
3) Oxygen is the final electron acceptor, being reduced to water along with protons in Complex IV. This chemiosmotic mechanism couples electron transport to ATP synthesis via the proton gradient across the inner mitochondrial membrane
Respiration is the process by which plants release energy stored during photosynthesis. There are two types of respiration - aerobic respiration which requires oxygen and occurs in the mitochondria, and anaerobic respiration which does not require oxygen. Respiration involves several stages including glycolysis, the Krebs cycle, and the electron transport chain, which ultimately generate ATP through oxidative phosphorylation. Respiration is essential for plant growth and metabolism as it provides energy for cellular processes and converts stored energy into usable form.
Chapter 19 - Oxidative Phosphorylation and Photophosphorylation- BiochemistryAreej Abu Hanieh
The document discusses two processes that cells use to synthesize ATP - oxidative phosphorylation and photophosphorylation. Both processes involve the flow of electrons through electron transport chains to establish a proton gradient across a membrane. In oxidative phosphorylation, the proton gradient is used by ATP synthase to phosphorylate ADP, while in photophosphorylation light provides the energy to drive the process in chloroplasts. The chemiosmotic theory proposes that it is the flow of protons back through ATP synthase, not a direct chemical reaction, that provides the energy for ATP synthesis.
Oxidative phosphorylation and photophosphorylation are the two main mechanisms by which organisms generate ATP. In oxidative phosphorylation, electrons are passed through an electron transport chain in mitochondria to reduce oxygen to water, pumping protons across the inner mitochondrial membrane. The resulting proton gradient is used by ATP synthase to phosphorylate ADP to ATP. Photophosphorylation uses sunlight to drive electron transport and proton pumping across thylakoid membranes in chloroplasts to similarly synthesize ATP. Both mechanisms conserve the energy of electron transport as a proton gradient that is then used to power ATP synthesis, demonstrating the fundamental similarity between these critical energy conversion processes.
The document provides information about energy and how ATP is used to store and transport energy in cells. It discusses how ATP is formed through cellular respiration, with glycolysis generating ATP without oxygen and the Krebs cycle and electron transport chain producing more ATP with oxygen. Photosynthesis is also summarized, explaining how plants use sunlight to convert carbon dioxide and water into glucose and oxygen through light-dependent and light-independent reactions.
This document provides an overview of photosynthesis and the dark reaction phase. It discusses key topics like the Calvin cycle, the structures of chloroplasts, and the C4 and CAM pathways. The Calvin cycle fixes carbon dioxide into organic molecules like glucose. It consists of carbon fixation, reduction reactions, and ribulose bisphosphate regeneration. The C4 pathway occurs in some plants and involves a four-carbon compound to concentrate carbon dioxide and prevent photorespiration. CAM plants open their stomata at night to fix carbon dioxide into malic acid, then release it for the Calvin cycle during the day.
Photosynthesis has two phases: the light reaction and dark reaction. The light reaction uses photosynthetic pigments like chlorophyll to convert solar energy into chemical energy in the form of ATP and NADPH. It occurs in the thylakoid membranes of chloroplasts. The dark reaction uses these products to fix carbon and produce sugars. The light reaction involves three steps: excitation of photosystems, production of ATP via electron transport, and reduction of NADP+ and photolysis of water. This is summarized by the Z-scheme which represents the electron flow and energy changes. Photophosphorylation uses the proton gradient generated by electron transport to synthesize ATP via chemiosmosis.
The document summarizes the stages of aerobic respiration in bacteria. It begins with glycolysis which produces pyruvic acid and ATP without oxygen. The Krebs cycle then converts pyruvate into carbon dioxide while producing more ATP and NADH. Finally, the electron transport chain uses the NADH to power ATP synthesis via chemiosmosis. Overall, the aerobic respiration of one glucose molecule yields 38 ATP.
The document provides information on cellular respiration and how it generates ATP through oxidative phosphorylation in the mitochondria. It discusses the electron transport chain, made up of protein complexes I-IV in the inner mitochondrial membrane, which establishes a proton gradient by pumping protons from the matrix to the intermembrane space. This proton gradient drives ATP synthase to catalyze the phosphorylation of ADP to ATP. The chemiosmotic theory explains how the potential energy in the proton gradient is used to produce ATP through rotation of the ATP synthase complex.
This document discusses Rubisco, the most abundant enzyme on Earth, which catalyzes the first major step of photosynthesis and photorespiration. Rubisco exists in two forms with different functions - RuBP carboxylase, which catalyzes the first step of photosynthesis, and RuBP oxygenase, which catalyzes the first step of the wasteful process of photorespiration. The document outlines the conditions that favor each form and describes photorespiration in C3, C4, and CAM plants. It also discusses the significance and factors affecting photosynthesis.
Electron transport chain and Oxidative phosphorylationmeghna91
The document summarizes electron transport chain (ETC) and oxidative phosphorylation. It describes that NADH and FADH2 produced during metabolism are oxidized via ETC complexes I-IV to create a proton gradient, then ATP synthase uses this gradient to synthesize ATP. The ETC consists of Complexes I-V located in the inner mitochondrial membrane, with Complexes I, III, and IV pumping protons from the matrix to the intermembrane space during electron transfer, building up proton motive force used by Complex V to drive ATP synthesis from ADP and phosphate.
Metabolism involves catabolic and anabolic reactions. Catabolism breaks down molecules to generate energy, while anabolism uses energy to build molecules. Glycolysis and the Krebs cycle oxidize glucose to produce ATP and NADH/FADH2. During oxidative phosphorylation, electrons are passed through an electron transport chain to power ATP synthesis. Fermentation occurs without oxygen and regenerates NAD+ by converting pyruvate into other products like lactic acid or ethanol. Organisms are classified nutritionally based on their energy and carbon sources.
Photosynthesis is the process by which plants, algae, and cyanobacteria use sunlight, water and carbon dioxide to produce oxygen and energy in the form of ATP and NADPH. It occurs in two phases: the light-dependent reactions and the light-independent reactions. The light reactions capture energy from sunlight and use it to make ATP and NADPH. The Calvin cycle uses these products to incorporate carbon from carbon dioxide into organic compounds to fuel the plant. Some plants use alternative pathways like C4 or CAM photosynthesis that help reduce photorespiration and increase water use efficiency.
1. Photosynthesis involves two main stages - the light dependent reaction where light energy is captured to make ATP and NADPH, and the light independent Calvin cycle where CO2 is fixed using ATP and NADPH to produce glucose.
2. The light reactions take place in the thylakoid membranes of chloroplasts and involve the photsytems which transfer electrons to make ATP and NADPH.
3. The Calvin cycle takes place in the stroma of the chloroplast and uses ATP and NADPH to convert CO2 into glucose through a series of reduction and phosphorylation reactions.
The document summarizes the process of photosynthesis. It describes how photosynthesis takes place in chloroplasts, which contain chlorophyll pigments embedded in the thylakoid membrane. The pigments absorb light energy which is used to transfer electrons along the membrane. This powers the synthesis of ATP and NADPH, providing chemical energy. The light reactions are followed by the dark reactions, where carbon dioxide is fixed and organic molecules like glucose are produced in the Calvin cycle within the chloroplast stroma.
The document summarizes key aspects of oxidative phosphorylation and ATP production in mitochondria. It describes how electrons from NADH and FADH2 are transferred through electron transport chain complexes I-IV, pumping protons out of the mitochondrial matrix. This generates a proton gradient that drives ATP synthase to phosphorylate ADP to ATP. The coupling of electron transport and ATP production via this proton gradient is explained by Mitchell's chemiosmotic theory.
The document summarizes cellular respiration and the production of ATP through oxidative phosphorylation. It discusses how carbohydrates, fats, and amino acids are broken down to feed into the electron transport chain, whose purpose is to release energy to drive the synthesis of ATP from ADP and inorganic phosphate. The process occurs within the inner mitochondrial membrane in complexes of the electron transport chain, and generates more ATP per pair of electrons carried through when NADH is oxidized compared to FADH2. The availability of ADP regulates the rate of ATP production. Oxygen consumption and ADP levels increase under conditions when ATP is needed at a rapid rate, such as during exercise. Some physiological and synthetic uncoupling agents can disrupt this phosphorylation process
This document contains multiple sections from lectures by Dr. Ashok Kumar J on the topic of cellular respiration and oxidative phosphorylation. It discusses key concepts such as oxidation, reduction, the electron transport chain, ATP synthase, the chemiosmotic theory proposed by Peter Mitchell, and disorders that can result from mitochondrial dysfunction.
Biological oxidation (part - III) Oxidative PhosphorylationAshok Katta
Biological oxidation (part - III) Oxidative Phosphorylation
- Mechanism of Oxidative Phosphorylation
-- Chemiosmotic theory
-P:O Ratio
Substrate Level Phosphorylation
Shuttle Systems for Oxidation of Extramitochondrial NADH
1) Oxidative phosphorylation uses electron transport chain complexes in the mitochondrial inner membrane to generate ATP from ADP and inorganic phosphate. As electrons are passed through Complexes I-IV, protons are pumped from the matrix to the intermembrane space, building an electrochemical gradient.
2) Protons flow back through ATP synthase, driving the phosphorylation of ADP to ATP in the matrix. The electron carriers, including ubiquinone and cytochrome c, shuttle electrons and protons between the complexes.
3) Oxygen is the final electron acceptor, being reduced to water along with protons in Complex IV. This chemiosmotic mechanism couples electron transport to ATP synthesis via the proton gradient across the inner mitochondrial membrane
Respiration is the process by which plants release energy stored during photosynthesis. There are two types of respiration - aerobic respiration which requires oxygen and occurs in the mitochondria, and anaerobic respiration which does not require oxygen. Respiration involves several stages including glycolysis, the Krebs cycle, and the electron transport chain, which ultimately generate ATP through oxidative phosphorylation. Respiration is essential for plant growth and metabolism as it provides energy for cellular processes and converts stored energy into usable form.
Chapter 19 - Oxidative Phosphorylation and Photophosphorylation- BiochemistryAreej Abu Hanieh
The document discusses two processes that cells use to synthesize ATP - oxidative phosphorylation and photophosphorylation. Both processes involve the flow of electrons through electron transport chains to establish a proton gradient across a membrane. In oxidative phosphorylation, the proton gradient is used by ATP synthase to phosphorylate ADP, while in photophosphorylation light provides the energy to drive the process in chloroplasts. The chemiosmotic theory proposes that it is the flow of protons back through ATP synthase, not a direct chemical reaction, that provides the energy for ATP synthesis.
Oxidative phosphorylation and photophosphorylation are the two main mechanisms by which organisms generate ATP. In oxidative phosphorylation, electrons are passed through an electron transport chain in mitochondria to reduce oxygen to water, pumping protons across the inner mitochondrial membrane. The resulting proton gradient is used by ATP synthase to phosphorylate ADP to ATP. Photophosphorylation uses sunlight to drive electron transport and proton pumping across thylakoid membranes in chloroplasts to similarly synthesize ATP. Both mechanisms conserve the energy of electron transport as a proton gradient that is then used to power ATP synthesis, demonstrating the fundamental similarity between these critical energy conversion processes.
The document provides information about energy and how ATP is used to store and transport energy in cells. It discusses how ATP is formed through cellular respiration, with glycolysis generating ATP without oxygen and the Krebs cycle and electron transport chain producing more ATP with oxygen. Photosynthesis is also summarized, explaining how plants use sunlight to convert carbon dioxide and water into glucose and oxygen through light-dependent and light-independent reactions.
This document provides an overview of photosynthesis and the dark reaction phase. It discusses key topics like the Calvin cycle, the structures of chloroplasts, and the C4 and CAM pathways. The Calvin cycle fixes carbon dioxide into organic molecules like glucose. It consists of carbon fixation, reduction reactions, and ribulose bisphosphate regeneration. The C4 pathway occurs in some plants and involves a four-carbon compound to concentrate carbon dioxide and prevent photorespiration. CAM plants open their stomata at night to fix carbon dioxide into malic acid, then release it for the Calvin cycle during the day.
Photosynthesis has two phases: the light reaction and dark reaction. The light reaction uses photosynthetic pigments like chlorophyll to convert solar energy into chemical energy in the form of ATP and NADPH. It occurs in the thylakoid membranes of chloroplasts. The dark reaction uses these products to fix carbon and produce sugars. The light reaction involves three steps: excitation of photosystems, production of ATP via electron transport, and reduction of NADP+ and photolysis of water. This is summarized by the Z-scheme which represents the electron flow and energy changes. Photophosphorylation uses the proton gradient generated by electron transport to synthesize ATP via chemiosmosis.
The document summarizes the stages of aerobic respiration in bacteria. It begins with glycolysis which produces pyruvic acid and ATP without oxygen. The Krebs cycle then converts pyruvate into carbon dioxide while producing more ATP and NADH. Finally, the electron transport chain uses the NADH to power ATP synthesis via chemiosmosis. Overall, the aerobic respiration of one glucose molecule yields 38 ATP.
The document provides information on cellular respiration and how it generates ATP through oxidative phosphorylation in the mitochondria. It discusses the electron transport chain, made up of protein complexes I-IV in the inner mitochondrial membrane, which establishes a proton gradient by pumping protons from the matrix to the intermembrane space. This proton gradient drives ATP synthase to catalyze the phosphorylation of ADP to ATP. The chemiosmotic theory explains how the potential energy in the proton gradient is used to produce ATP through rotation of the ATP synthase complex.
This document discusses Rubisco, the most abundant enzyme on Earth, which catalyzes the first major step of photosynthesis and photorespiration. Rubisco exists in two forms with different functions - RuBP carboxylase, which catalyzes the first step of photosynthesis, and RuBP oxygenase, which catalyzes the first step of the wasteful process of photorespiration. The document outlines the conditions that favor each form and describes photorespiration in C3, C4, and CAM plants. It also discusses the significance and factors affecting photosynthesis.
Electron transport chain and Oxidative phosphorylationmeghna91
The document summarizes electron transport chain (ETC) and oxidative phosphorylation. It describes that NADH and FADH2 produced during metabolism are oxidized via ETC complexes I-IV to create a proton gradient, then ATP synthase uses this gradient to synthesize ATP. The ETC consists of Complexes I-V located in the inner mitochondrial membrane, with Complexes I, III, and IV pumping protons from the matrix to the intermembrane space during electron transfer, building up proton motive force used by Complex V to drive ATP synthesis from ADP and phosphate.
Metabolism involves catabolic and anabolic reactions. Catabolism breaks down molecules to generate energy, while anabolism uses energy to build molecules. Glycolysis and the Krebs cycle oxidize glucose to produce ATP and NADH/FADH2. During oxidative phosphorylation, electrons are passed through an electron transport chain to power ATP synthesis. Fermentation occurs without oxygen and regenerates NAD+ by converting pyruvate into other products like lactic acid or ethanol. Organisms are classified nutritionally based on their energy and carbon sources.
Photosynthesis is the process by which plants, algae, and cyanobacteria use sunlight, water and carbon dioxide to produce oxygen and energy in the form of ATP and NADPH. It occurs in two phases: the light-dependent reactions and the light-independent reactions. The light reactions capture energy from sunlight and use it to make ATP and NADPH. The Calvin cycle uses these products to incorporate carbon from carbon dioxide into organic compounds to fuel the plant. Some plants use alternative pathways like C4 or CAM photosynthesis that help reduce photorespiration and increase water use efficiency.
1. Photosynthesis involves two main stages - the light dependent reaction where light energy is captured to make ATP and NADPH, and the light independent Calvin cycle where CO2 is fixed using ATP and NADPH to produce glucose.
2. The light reactions take place in the thylakoid membranes of chloroplasts and involve the photsytems which transfer electrons to make ATP and NADPH.
3. The Calvin cycle takes place in the stroma of the chloroplast and uses ATP and NADPH to convert CO2 into glucose through a series of reduction and phosphorylation reactions.
The document summarizes the process of photosynthesis. It describes how photosynthesis takes place in chloroplasts, which contain chlorophyll pigments embedded in the thylakoid membrane. The pigments absorb light energy which is used to transfer electrons along the membrane. This powers the synthesis of ATP and NADPH, providing chemical energy. The light reactions are followed by the dark reactions, where carbon dioxide is fixed and organic molecules like glucose are produced in the Calvin cycle within the chloroplast stroma.
Photosynthesis occurs in three main steps:
1) Light-dependent reactions in the chloroplast thylakoid membrane use light energy to produce ATP and NADPH via the electron transport chain.
2) The Calvin cycle uses ATP and NADPH to fix carbon from CO2 into 3-carbon sugar phosphates, which are then reduced and regenerated to produce G3P.
3) G3P molecules are combined to form glucose, providing an energy-storing organic compound for cells. The oxygen produced as a byproduct is released for other organisms to use.
Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, water and carbon dioxide to produce oxygen and energy in the form of glucose. It takes place in chloroplasts and involves two stages - the light-dependent reactions where energy from sunlight is captured and converted to chemical energy in the form of ATP and NADPH, and the light-independent reactions where carbon dioxide is fixed into organic compounds like glucose using the ATP and NADPH produced in the light reactions. Many environmental factors like temperature, light intensity, water availability and carbon dioxide concentration can affect the rate of photosynthesis.
The document discusses the evolution of the carbon concentrating mechanism (CCM) in cyanobacteria. It describes how cyanobacteria developed effective CCMs over billions of years as atmospheric CO2 levels declined. The CCM allows cyanobacteria to concentrate CO2 up to 1000-fold near Rubisco. The key components of the CCM, including carboxysomes, inorganic carbon transporters, and carbonic anhydrases, are examined. The diversity of these components across cyanobacterial lineages is also reviewed.
In this ppt, you will learn about photosystem first of photosynthesis, with video and animation such a nice presentation. electron movement by animation, see and understand the system.
Photosynthesis converts light energy to chemical energy through light reaction. Light reaction occurs in the thylakoid membranes of chloroplasts, where photosystems use light to transfer electrons and pump protons, generating ATP and NADPH. There are two photosystems - PSII uses water as the electron donor and evolves oxygen, while PSI and cytochrome b6f complex generate a proton gradient used for ATP synthesis via ATP synthase. Both oxygenic and anoxygenic bacteria perform similar light reactions, though they use different electron donors and may contain only one photosystem. Light reaction is essential for providing the energy required for carbon fixation in photosynthesis.
Ph0tosystemPhotosystem: Reaction center surrounded by several light-harvestin...AMRITHA K.T.K
Photosynthesis has two photosystems, Photosystem I and Photosystem II, that work sequentially to harness light energy to produce chemical energy. Photosystem II uses light energy to split water, releasing electrons that are transferred through an electron transport chain, pumping protons across the membrane and producing oxygen. The energized electrons are then passed to Photosystem I, which uses them to reduce NADP+ to NADPH to be used in the Calvin cycle for carbon fixation. Together, the two photosystems convert light energy to chemical energy in the form of ATP and NADPH.
This document provides an overview of photosynthesis presented by a group of 6 students. It describes the key processes and phases of photosynthesis including light reaction, dark reaction, photophosphorylation, photosystems, and alternative pathways such as C4 and CAM photosynthesis. The light reaction uses energy from sunlight to split water and produce ATP and NADPH. The dark reaction then uses these products to fix carbon from carbon dioxide into sugars.
1) The document is an assignment submission on the electron transport chain from a student at PrimeAsia University.
2) It provides an overview of the electron transport chain as a series of protein complexes in the mitochondrial inner membrane that pass electrons from NADH and FADH2 through redox reactions to generate a proton gradient.
3) This proton gradient is then used by ATP synthase to produce ATP through chemiosmosis, completing oxidative phosphorylation.
The document outlines the process of photosynthesis through 6 main topics: plant structure, pigments and absorbance spectrum, light-dependent reactions, Calvin cycle, and photorespiration. It discusses the key organelles and structures involved in photosynthesis in plant leaves like chloroplasts, stomata, and mesophyll tissue. It also explains the light and dark reactions of photosynthesis, including the light-dependent reaction where light energy is captured and the Calvin cycle where carbon is fixed into glucose.
Photosystem I is located in the membrane of cyanobacteria and plants. It contains proteins, chlorophylls, carotenoids, and other cofactors that transfer electrons during photosynthesis. PsaA and PsaB form the core where primary electron transfer occurs. Electrons are transferred from P700 to ferredoxin via a chain containing chlorophyll, phylloquinone, and iron-sulfur clusters. Ferredoxin then transfers electrons to ferredoxin-NADP+ reductase to reduce NADP+ to NADPH, providing energy for the Calvin cycle.
1. The light reaction of photosynthesis occurs in the thylakoid membranes of chloroplasts and involves the absorption of light by photosynthetic pigments.
2. Energy from the absorbed light is used to transfer electrons along an electron transport chain, powering the synthesis of ATP through photophosphorylation and reducing NADP+ to NADPH.
3. The products of the light reaction, ATP and NADPH, are used in the Calvin cycle to fix carbon from CO2 into organic molecules like glucose.
this presentation contains briefing of the chapter as per NCERT syllabus in details that contains photosynthesis process, early experiments, photosynthetic pigments,photophosphorylation, light reactions and dark reactions n factors affecting photsynthesis.
Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, water and carbon dioxide to produce oxygen and energy in the form of glucose. It occurs in two stages: the light-dependent reactions and the light-independent reactions. The light-dependent reactions use energy from sunlight to produce ATP and NADPH through a process called photophosphorylation. The light-independent reactions, also called the Calvin cycle, use ATP and NADPH to fix carbon from carbon dioxide into organic molecules like glucose. The Calvin cycle is an enzyme-driven process where carbon is first fixed into the three-carbon molecule phosphoglycerate then reduced, regenerated, and used to produce glucose and other carbohydr
This document summarizes key aspects of photosynthesis. It describes that photosynthesis occurs in plants, algae, and photosynthetic bacteria. Light energy is captured and used to fix carbon from carbon dioxide into sugars, with oxygen as a byproduct. The process takes place in chloroplasts and involves two stages - the light reactions where ATP and NADPH are produced, and the dark reactions where CO2 is fixed into sugars. Pigments like chlorophyll and accessory pigments harvest light energy which is used to power electron transport and produce chemical energy carriers.
The document is an assignment submission on the electron transport chain. It provides details on the electron transport chain, including that it is a series of protein complexes in the mitochondrial inner membrane that sequentially transfers electrons, pumping protons out in the process. This generates a proton gradient that is then used by ATP synthase to produce ATP via chemiosmosis, making oxidative phosphorylation the most efficient ATP producer in aerobic respiration. The assignment covers the components, steps, and purpose of the electron transport chain in detail over multiple pages.
Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, water and carbon dioxide to produce oxygen and energy in the form of glucose. It occurs in two stages - the light dependent reactions and the light independent reactions. In the light dependent reactions, chlorophyll absorbs sunlight and uses it to convert water to oxygen and produce ATP and NADPH. In the light independent reactions, also known as the Calvin cycle, the ATP and NADPH produced are used to convert carbon dioxide into glucose which provides energy for plant growth. Photosynthesis is essential as it produces the oxygen and food on which nearly all life on Earth depends.
Bioenergetics is an important domain in biology. This presentation has explored ATP production and its optimum utilization in biological systems along with certain theories and experiments to give a bird's eye view of this important issue.
The document discusses bioenergetics, which focuses on how cells transform energy through processes like cellular respiration and photosynthesis. These bioenergetic processes are essential to life. ATP (adenosine triphosphate) is the molecule that cells use to store and transport energy. ATP is produced through catabolic pathways that break down molecules and through phosphorylation, either substrate-level or oxidative phosphorylation during cellular respiration. Photosynthesis uses light energy to produce sugars and oxygen from carbon dioxide and water. This involves two stages - the light-dependent reactions where ATP and NADPH are produced, and the Calvin cycle where sugars are formed.
Photosynthesis occurs in two stages: the light reactions and the Calvin cycle. In the light reactions, solar energy is converted to ATP and NADPH through photosystems in the thylakoid membranes. The Calvin cycle then uses ATP and NADPH to incorporate CO2 into organic molecules like glucose. Photosynthesis is essential as it produces oxygen and stores solar energy in sugars that fuel life on Earth.
(1) Chloroplasts contain the light-dependent reactions of photosynthesis, which capture energy from sunlight and use it to produce ATP and NADPH. (2) These reactions occur in the thylakoid membranes through two photosystems that absorb light and transfer electrons. This powers an electron transport chain that pumps protons across the membrane. (3) The resulting proton gradient drives ATP synthesis when protons diffuse back through ATP synthase. Oxygen is also released as a byproduct of splitting water.
light reaction of photosynthesis (botany)PriyanshiRaj9
(1) Chloroplasts contain the light-dependent reactions of photosynthesis, which capture energy from sunlight and use it to produce ATP and NADPH. (2) These reactions occur in the thylakoid membranes through two photosystems that absorb light and transfer electrons. This powers an electron transport chain that pumps protons across the membrane. (3) The resulting proton gradient drives ATP synthesis when protons diffuse back through ATP synthase. Oxygen is also released as a byproduct of splitting water.
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1. Photosystems are functional and structural units of protein complexes involved in
photosynthesis that together carry out the primary photochemistry of photosynthesis: the
absorption of light and the transfer of energy and electrons. They are found in the thylakoid
membranes of plants, algae and cyanobacteria (in plants and algae these are located in the
chloroplasts), or in the cytoplasmic membrane of photosynthetic bacteria.
[edit] Reaction centers
At the heart of a photo system lies the Reaction Center, which is an enzyme that uses light to
reduce molecules. In a photo system, this Reaction Center is surrounded by light-harvesting
complexes that enhance the absorption of light and transfer the energy to the Reaction Centers.
Light-Harvesting and Reaction Center complexes are membrane protein complexes that are
made of several protein-subunits and contain numerous cofactors. In the photosynthetic
membranes, reaction centers provide the driving force for the bioenergetic electron and proton
transfer chain. When light is absorbed by a reaction center (either directly or passed by
neighbouring pigment-antennae), a series of oxido-reduction reactions is initiated, leading to the
reduction of a terminal acceptor. Two families of reaction centers in photosystems exist: type I
reaction centers (such as photo system I (P700) in chloroplasts and in green-sulphur bacteria) and
type II reaction centers (such as photosystem II (P680) in chloroplasts and in non-sulphur purple
bacteria). Each photosystem can be identified by the wavelength of light to which it is most
reactive (700 and 680 nanometers, respectively for PSI and PSII in chloroplasts), the amount and
type of light-harvesting complexes present and the type of terminal electron acceptor used. Type
I photosystems use ferredoxin-like iron-sulfur cluster proteins as terminal electron acceptors,
while type II photosystems ultimately shuttle electrons to a quinone terminal electron acceptor.
One has to note that both reaction center types are present in chloroplasts and cyanobacteria,
working together to form a unique photosynthetic chain able to extract electrons from water,
creating oxygen as a byproduct.
[edit] Structure
A reaction center comprises several (>10 or >11) protein subunits, providing a scaffold for a
series of cofactors. The latter can be pigments (like chlorophyll, pheophytin, carotenoids),
quinones, or iron-sulfur clusters.
[edit] Relationship between Photosystems I and II
For oxygenic photosynthesis, both photosystems I and II are required. Oxygenic photosynthesis
can be performed by plants and cyanobacteria; cyanobacteria are believed to be the progenitors
of the photosystem-containing chloroplasts of eukaryotes. Photosynthetic bacteria that cannot
produce oxygen have a single photosystem called BRC, bacterial reaction center.
2. The photosystem I was named "I" since it was discovered before photosystem II, but this does
not represent the order of the electron flow.
When photosystem II absorbs light, electrons in the reaction-center chlorophyll are excited to a
higher energy level and are trapped by the primary electron acceptors. To replenish the deficit of
electrons, electrons are extracted from water by a cluster of four Manganese ions in photosystem
II and supplied to the chlorophyll via a redox-active tyrosine.
Photoexcited electrons travel through the cytochrome b6f complex to photosystem I via an
electron transport chain set in the thylakoid membrane. This energy fall is harnessed, (the whole
process termed chemiosmosis), to transport hydrogen (H+) through the membrane, to the lumen,
to provide a proton-motive force to generate ATP. The protons are transported by the
plastoquinone. If electrons only pass through once, the process is termed noncyclic
photophosphorylation.
When the electron reaches photosystem I, it fills the electron deficit of the reaction-center
chlorophyll of photosystem I. The deficit is due to photo-excitation of electrons that are again
trapped in an electron acceptor molecule, this time that of photosystem I.
ATP is generated when the ATP synthase transports the protons present in the lumen to the
stroma, through the membrane. The electrons may either continue to go through cyclic electron
transport around PS I or pass, via ferredoxin, to the enzyme NADP+ reductase. Electrons and
hydrogen ions are added to NADP+ to form NADPH. This reducing agent is transported to the
Calvin cycle to react with glycerate 3-phosphate, along with ATP to form glyceraldehyde 3-
phosphate, the basic building-block from which plants can make a variety of substances
Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the
Light-dependent reactions. It is located in the thylakoid membrane of plants, algae, and
cyanobacteria. The enzyme captures photons of light to energize electrons that are then
transferred through a variety of coenzymes and cofactors to reduce plastoquinone to
plastoquinol. The energized electrons are replaced by oxidizing water to form hydrogen ions and
molecular oxygen. By obtaining these electrons from water, photosystem II provides the
electrons for all of photosynthesis to occur. The hydrogen ions (protons) generated by the
oxidation of water help to create a proton gradient that is used by ATP synthase to generate ATP.
The energized electrons transferred to plastoquinone are ultimately used to reduce NADP+ to
NADPH or are used in Cyclic Photophosphorylation.
Structure
3. Cyanobacteria photosystem II, Monomer, PDB 2AXT.
Photosystem II (of cyanobacteria and green plants) is composed of around 20
subunits(depending on the organism) as well as other accessory, light-harvesting proteins. Each
photosystem II contains at least 99 cofactors: 35 chlorophyll a, 12 beta-carotene, two pheophytin,
two plastoquinone, two heme, one bicarbonate, 20 lipid, the Mn4CaO5 cluster (including chloride
ion), and one non heme Fe2+ and two putative Ca2+ ion per monomer.[1] There are different
crystal structures of photosystem II. The PDB accession codes for this protein are 3ARC,3BZ1,
3BZ2(3BZ1 and 3BZ2 are monomeric structures of the Photosystem II dimer) [1] 2AXT, 1S5L,
1W5C, 1ILX, 1FE1, 1IZL.
Photosystem II Light Harvesting complex
protein
Identifiers
Symbol PSII
Pfam PF00421
InterPro IPR000932
TCDB 3.E.2
OPM superfamily 2
4. OPM protein 3arc
[show]Available protein structures:
Protein Subunits (only with known
function)
Subunit Function
Reaction center Protein, binds Chlorophyll P680,
pheophytin,
D1
beta-carotene,quinone and manganese center
D2 Reaction center Protein
CP43 Binds manganese center
CP47
PsbO Manganese Stabilizing Protein
Coenzymes/Cofactors
Molecule Function
Chlorophyll Absorbs light
Beta-Carotene quench excess photoexcitation energy
Heme b559 also Protoporphyrin IX containing iron
Pheophytin Primary electron acceptor
Plastoquinone Mobile intra-thylakoid membrane electron carrier
Manganese center also known as the oxygen evolving center, or OEC
[edit] Oxygen-Evolving Complex (OEC)
Proposed structure of Manganese Center
The oxygen-evolving complex is the site of water oxidation. It is a metallo-oxo cluster
comprising four manganese ions (in oxidation states ranging from +3 to +5) and one divalent
calcium ion. When it oxidizes water, producing dioxygen gas and protons, it sequentially
5. delivers the four electrons from water to a tyrosine (D1-Y161) sidechain and then to P680 itself.
The structure of the oxygen-evolving complex is still contentious. The structures obtained by X-
ray crystallography are particularly controversial, since there is evidence that the manganese
atoms are reduced by the high-intensity X-rays used, altering the observed OEC structure.
However, crystallography in combination with a variety of other (less damaging) spectroscopic
methods such as EXAFS and electron paramagnetic resonance have given a fairly clear idea of
the structure of the cluster. One possibility is the cubane-like structure.[2] In 2011 the OEC of
PSII was resolved to a level of 1.9 angstroms revealing five oxygen atoms serving as oxo bridges
linking the five metal atoms and four water molecules bound to the Mn4CaO5 cluster; more than
1,300 water molecules were found in each photosystem II monomer, some forming extensive
hydrogen-bonding networks that may serve as channels for protons, water or oxygen
molecules.[3]
[edit] Water splitting
Water-splitting process: Electron transport and regulation. The first level (A) shows the original
Kok model of the S-states cycling, the second level (B) shows the link between the electron
transport (S-states advancement) and the relaxation process of the intermediate S-states ([YzSn],
n=0,1,2,3) formation
Photosynthetic water splitting (or oxygen evolution) is one of the most important reactions on the
planet, since it is the source of nearly all the atmosphere's oxygen. Moreover, artificial
photosynthetic water-splitting may contribute to the effective use of sunlight as an alternative
energy-source.
The mechanism of water oxidation is still not fully elucidated, but we know many details about
this process. The oxidation of water to molecular oxygen requires extraction of four electrons
and four protons from two molecules of water. The experimental evidence that oxygen is
released through cyclic reaction of oxygen evolving complex (OEC) within one PSII was
provided by Pierre Joliot et al.[4] They have shown that, if dark-adapted photosynthetic material
(higher plants, algae, and cyanobacteria) is exposed to a series of single turnover flashes, oxygen
evolution is detected with typical period-four damped oscillation with maxima on the third and
the seventh flash and with minima on the first and the fifth flash (for review see [5]). Based on
this experiment, Bessel Kok and co-workers [6] introduced a cycle of five flash-induced
6. transitions of the so-called S-states, describing the four redox states of OEC: When four
oxidizing equivalents have been stored (at the S4-state), OEC returns to its basic and in the dark
stable S0-state. Finally, the intermediate S-states [7] were proposed by Jablonsky and Lazar as a
regulatory mechanism and link between S-states and tyrosine Z.
Cyclic photophosphorylation is the production of some ATP in the light dependent stage of
photosynthesis. No photoylsis of water occurs and therefore no reduced NADP is produced
either. Only photosystem one is involved here and as light is absorbed by the photosystem, two
electrons are released which are accepted by the electron transfer chain. As the electrons are
transferred along the chain, energy is released which pumps protons across the thylakoid
membrane. A proton gradient forms and the protons diffuse through protein channels associated
with ATP synthase enzymes, the proton motive force along with the enzyme combine ADP and
inorganic phosphate atom to create ATP. The flow of protons which creates the ATP is
chemiosmosis. The ATP can then be used in the light independent stage of photosynthesis or to
actively transport potassium ions into the guard cells, so they become turgid as a result of water
entering by osmosis. This causes the stomata to open and carbon dioxide can readily diffuse in -
increasing the rate of photosynthesis
Light-Dependent and Light-Independent Reactions
The light reactions, or the light-dependent reactions, are up first. We call them either and both
names. The whole process looks a little like this:
Do not freak out or fill your head with all the complicated names in that diagram. No—stop right
there. All in all, the process is simpler than it looks. In the light-dependent reactions of
photosynthesis, the energy from light propels the electrons from a photosystem into a high-energy
7. state. In plants, there are two photosystems, aptly named Photosystem I and Photosystem II,
located in the thylakoid membrane of the chloroplast. The thylakoid membrane absorbs photon
energy of different wavelengths of light.
Here again is our friend the chloroplast. All exposed the way he is, he kind of reminds us of a boat
with green checkers in it:
Image source
Even though the two photosystems absorb different wavelengths of light, they work similarly. Each
photosystem is made of many different pigments. Some of these pigments can be described as
absorption pigments, and others are considered action pigments.
The absorption pigments transfer the energy from sunlight to another pigment; at each transfer,
the absorption pigments pass the photon energy to another pigment that absorbs a similar or lower
wavelength of light. Remember when we said that light is funky and acts like it has both particles and
waves? A photon is what we call the particle-like aspect of light. In other words, a photon is the basic
unit of light.
8. Anyway, eventually, the energy makes it to the reaction center, or action pigment. At this point, the
photosystem loses a highly charged electron to adjacent oxidizing agents, or electron acceptors, in
the electron transport chain. TSince the photosystem has lost an electron, it no longer has a
neutral charge and has instead become a positively charged photosystem.
The positively charged photosystem creates a scenario similar to one that might occur if Twilight
stars Robert Pattinson and Kristen Stewart made a surprise appearance at your local high school.
You, like the electrons in the photosystem, would be attracted to their presence even if you hated
them. (You would. Admit it.) The positively charged photosystem attracts electrons from water (H2O)
that can then be excited by light energy. When exactly four electrons are removed from H2O, oxygen
(O2) is generated. Why, you ask? If two water molecules have four hydrogens that lose four
electrons, exactly four hydrogen ions (H+) and two oxygens are left. Don't believe us? Count it out
for yourself.
4
Side note: since hydrogen normally only has 1 proton and 1 electron, the four hydrogen atoms that
have each lost one electron are each referred to as H+. Since each H+ is now without an electron,
there is only one proton remaining in the hydrogen atom. At some point, scientists became lazy and
started equating H+ with the word proton. If you think about it, they are in fact equivalent.
Back to regularly scheduled programming. The protons are then moved into the thylakoid lumen of
the chloroplast using the power of the electron transport chain. This move results in a higher
concentration of protons in the lumen than in the stroma of the chloroplast.
With so much positivity around, the protons get a little upset and try to equalize their distribution in
the chloroplast by moving from the lumen to the stroma to reach equilibrium (read: equal numbers
of protons in both places). The rush of protons moving into the stroma is called a proton gradient.
When protons move down the gradient, with down referring to the direction of the area containing
fewer protons, the protons are grabbed by enzymes that bring the protons together with the
electrons from the electron transport chain. This event ultimately results in the making of adenosine
triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH) from the
adenosine diphosphate (ADP) and nicotinamide adenine dinucleotide phosphate ion (NADP+)
that were hanging around nearby.
Now that everyone is partying it up in the stroma, it becomes the perfect location for the next stage
of photosynthesis, the light-independent reactions.
Pictures are worth the thousand words that may or may not have just whizzed by your head as you
were reading. Here is a much-simplified version of the earlier picture:
9. Did you miss something, or do we just suck at drawing these pictures? Nope. Photosystem II is
ahead of Photosystem I. You might ask, "What the heck happened, Shmoop?" Well, scientists
actually discovered Photosystem II before Photosystem I, and instead of changing the names when
they found the other photosystem, they just named them in reverse. We know; it's very annoying.
As you€™ve probably gathered by now, the light-dependent reactions fuel the second stage of
photosynthesis called the light-independent reactions. Our good buddy carbon dioxide (CO2)
provides an excellent source of carbon for making carbohydrates. However, conversion of one mole
(one mole is an amount equal to 6.023 × 1023 molecules) of CO2 to one mole of the carbohydrate
CH2O requires a lot of energy. And we mean a lot.
Guess what? The ATP and NADPH generated in the earlier light Mreactions are strong reducing
agents (electron donors) and are able to donate the necessary electrons to make carbohydrates.
Altogether, the conversion of one mole of CO2 to one mole of CH2O requires two moles of NADPH
and three moles of ATP. If you do the math, that's a heck of a lot of molecules. The cell then uses
ATP and NADPH to make carbohydrates in the Calvin cycle. We could use a Calvin and Hobbes
cartoon right about now.
A key player in the Calvin cycle is ribulose-1,5-bisphosphate carboxylase oxygenase
(affectionately called RuBisCo—thank goodness for nicknames), an enzyme that "fixes" CO2 to a
10. 5-carbon compound called ribulose-1,5-bisphosphate (RuBP). The oxygen in CO2 is released as
H2O. Immediately after RuBisCo catalyzes the attachment of the carbon from CO2 to the 5-carbon
RuBP, the new 6-carbon compound is broken down into two 3-carbon compounds called
phosphoglycerate (PGA, and no, it does not know how to golf). Since these 3-carbon compounds
were the first compounds to be identified in the plants, they were named C3 plants. It was originally
thought that RuBisCo was catalyzing the attachment of carbon to a 2-carbon molecule to make a 3-
carbon molecule. Oopsies. And we thought RuBisCo was a cookie company at first, too.
RuBisCo is actually a poor enzyme. Sorry, RuBie. It is slow at catalyzing the attachment of CO2 to
RuBP. To make matters worse, RuBisCo is also capable of catalyzing another less-than-beneficial
reaction. This reaction is called photorespiration, and it occurs when the concentration of CO2
drops too low relative to the concentration of O2 in the cell. Photorespiration begins when RuBisCo
uses O2 instead of CO2 and adds it to RuBP.
While CO2 is eventually produced in this reaction, and O2 is consumed, the reaction does not seem
to produce any useful energy forms. The origination and purpose of photorespiration is controversial
and still under active study by scientists. In an attempt to overcome the deficiency of RuBisCo, the
plant cell produces a whopping ton of the enzyme. If this sounds slightly masochistic, it kind of is,
which is why photorespiration has been labeled an outdated evolutionary relic. However, RuBisCo is
thought to be the most abundant protein on Earth.2
Right…this not a moan fest about RuBisCo. We were explaining the Calvin cycle. When RuBisCo
catalyzes the attachment of CO2 to the 5-carbon RuBP, the Calvin cycle begins. Reactions are
initiated to rebuild RuBP from PGA. In this process, 1 molecule of glyceraldehyde-3-phosphate
(G3P), a 3-carbon sugar, is removed from the cycle. Altogether, 1 molecule of G3P is produced
using 3 molecules of CO2, 9 molecules of ATP, and 6 molecules of NADPH. This 3-carbon sugar can
be exported to the cytoplasm to make sucrose (a sugar and a carbohydrate), which is then moved
throughout the plant for energy use. Alternatively, sucrose can be converted into another
carbohydrate, starch, and then stored in the chloroplast as a type of energy reserve
11. Brain Snacks
There are carnivores that undergo photosynthesis. Meat-eating plants do not eat for energy; they eat
to obtain nutrients, such as nitrogen and phosphate, to build the proteins needed for photosynthesis.
Living organisms besides plants do photosynthesis. One "biological masterpiece," the sea slug
Elysia chlorotica, is able to conduct photosynthesis by extracting DNA and chloroplasts from its plant
food source. Sneaky, sneaky.
In seeded plants, chloroplasts do not develop unless the seedlings are exposed to light. This
process is called photomorphogenesis.3
Weed killers called herbicides work by targeting enzymes used in the light reactions of
photosynthesis. Come here, little chloroplasts.
The light-independent reactions of photosynthesis are chemical reactions that convert carbon
dioxide and other compounds into glucose. These reactions occur in the stroma, the fluid-filled
area of a chloroplast outside of the thylakoid membranes. These reactions take the light-
dependent reactions and perform further chemical processes on them. There are three phases to
12. the light-independent reactions, collectively called the Calvin cycle: carbon fixation, reduction
reactions, and ribulose 1,5-bisphosphate (RuBP) regeneration.
Despite its name, this process occurs only when light is available. Plants do not carry out the
Calvin cycle by night. They, instead, release sucrose into the phloem from their starch reserves.
This process happens when light is available independent of the kind of photosynthesis (C3
carbon fixation, C4 carbon fixation, and Crassulacean Acid Metabolism); CAM plants store
malic acid in their vacuoles every night and release it by day in order to make this process
work.[1]
Contents
[hide]
1 Coupling to other metabolic pathways
2 Light-dependent regulation
3 Further reading
4 External links
5 References
[edit] Coupling to other metabolic pathways
These dark reactions are closely coupled to the thylakoid electron transport chain as reducing
power provided by NADPH produced in the photosystem I is actively needed. The process of
photorespiration, also known as C2 cycle, is also coupled to the dark reactions, as it results from
an alternative reaction of the Rubisco enzyme, and its final byproduct is also another
glyceraldehyde-3-P.TYHHHHHHHHHHHHT
[edit] Light-dependent regulation
Main article: Light-dependent reactions
Despite its widespread names (both light-independent and dark reactions), these reactions do not
occur in the dark or at night. There is a light-dependent regulation of the cycle enzymes, as the
third step requires reduced NADP; and this process would be a waste of energy, as there is no
electron flow in the dark.
There are 2 regulation systems at work when the cycle needs to be turned on or off:
thioredoxin/ferredoxin activation system, which activates some of the cycle enzymes, and the
Rubisco enzyme activation, which involves its own activase.
The thioredoxin/ferredoxin system activates the enzymes glyeraldehyde-3-P dehydrogenase,
glyceraldehyde-3-P phosphatase, fructose-1,6-bisphosphatase, sedoheptulose-1,7-
13. bisphosphatase, and ribulose-5-phosphatase kinas, which are key points of the process. This
happens when light is available, as the ferredoxin protein is reduced in the photosystem I
complex of the thylakoid electron chain when electrons are circulating through it.[2] Ferredoxin
then binds to and reduces the thioredoxin protein, which activates the cycle enzymes by severing
a cystine bond found in all these enzymes. This is a dynamic process as the same bond is formed
again by other proteins that deactivate the enzymes. The implications of this process are that the
enzymes remain mostly activated by day and are deactivated in the dark when there is no more
reduced ferredoxin available.
The enzyme Rubisco has its own activation process, which involves a more complex process. It
is necessary that a specific lysine amino acid be carbamylated in order to activate the enzyme.
This lysine binds to RuBP and leads to a non-functional state if left uncarbamylated. A specific
activase enzyme, called Rubisco activase, helps this carbamylation process by removing one
proton from the lysine and making the binding of the carbon dioxide molecule possible. Even
then the Rubisco enzyme is not yet functional, as it needs a magnesium ion to be bound to the
lysine in order to function. This magnesium ion is released from the thylakoid lumen when the
inner PH drops due to the active pumping of protons from the electron flow. Rubisco activase
itself is activated by increased concentrations of ATP in the stroma caused by its phosphorylation
The light-independent reactions of photosynthesis
These involve the reduction of carbon dioxide using reduced NADP and ATP produced in the light-
dependent reactions of photosynthesis.
The reactions are known as the Calvin cycle, and they take place in the stroma of the chloroplast.
Pass the mouse pointer over this diagram for more information.
14. =[
Although the cycle is quite complicated, there are not too many compounds that need to be known
about at this level:
No of No of
Compound
C atoms phosphates
Ribulose bisphosphate
5 2
(RUBP)
15. Glycerate 3-phosphate
3 1
(GP)
Triose phosphate
3 1
(TP)
Ribulose monophosphate
5 1
(RuP)
There are effectively 3 stages to this process:
1) Carbon dioxide fixation
This process is called fixation because carbon dioxide from the air is converted into an organic
compound which cannot move away.
It is probably convenient to consider 6 molecules of carbon dioxide entering the cycle, so that the next
step below occurs 6 times.
Carbon dioxide reacts with ribulose bisphosphate RuBP.
For this reason RuBP is called a CO2 acceptor.
Yet another way of saying this is that RuBP is carboxylated.
This occurs under the influence of the enzyme ribulose bisphosphate carboxylase (RUBISCO) which is
said to be the most abundant protein on the planet.
Ribulose bisphosphate has 5 carbon atoms and 2 phosphate groups, and by accepting one more carbon
atom from CO2 it should be converted into a 6 carbon, 2 phosphate compound. However ...
This compound is immediately converted into 2 molecules of glycerate 3-phosphate (GP), which
contains 3 carbons and one phosphate group.
For every 6 molecules of CO2 entering the cycle, 12 molecules of GP are produced.
This pathway is called C3 carbon fixation because the first product is a 3-carbon compound. Some plants
have an alternative pathway - C4 carbon fixation - in which the 4-carbon compound oxalacetate (OAA) is
produced and others have a CAM pathway.
16. 2) Carbon dioxide reduction
There are several published versions of this section, varying in complexity, and using different
terminology.
This stage is so called because when CO2 reacts with H from reduced NADP it gains hydrogen and loses
oxygen to become CH2O, the empirical (simplest) formula for carbohydrates. Reduction is loss of oxygen,
or reaction with hydrogen, or gain of electrons. However the CO2 is now part of glycerate 3-phosphate
(GP).
Glycerate 3-phosphate (GP) is converted into triose phosphate (TP) using reduced NADP and ATP.
The reduced NADP provides the reducing power (hydrogen) and is converted back to NADP which is
then reduced again in the light-dependent reactions.
ATP is also used to provide energy for the conversion. It is converted into ADP + Pi, which are
reconverted into ATP in the light-dependent reactions.
Some of the triose phosphate (two molecules out of the twelve) is removed from the cycle, to be
converted into glucose, or other molecules such as starch, lipid or protein.
3) Ribulose bisphosphate regeneration
In a complex series of reactions, the remaining ten molecules of TP are converted into 6 molecules of
the 5-carbon compound ribulose monophosphate
(10x3C=6x5C, but some phosphates are lost from the cycle).
Ribulose monophosphate is converted into ribulose bisphosphate, using a phosphate group from ATP.
Ribulose bisphosphate reacts with/accepts carbon dioxide/becomes carboxylated, to keep the cycle
operating again ...