Photosynthesis
Capturing the Energy of Life
A. All organisms require energy.
B. Some organisms (autotrophs) obtain energy directly from the sun and store it in organic compounds (glucose) during a process called photosynthesis.
6CO2 + 6H2O + energy --> 6O2 + C6H12O6
Energy for Life Processes
A. Energy is the ability to do work.
B. Work for a cell includes growth & repair, active transport across cell membranes, reproduction, synthesis of cellular products, etc.
C. Work is the ability to change or move matter against other forces (W = F x D).
D. Autotrophs or producers convert sunlight, CO2, and H2O into glucose (their food).
E. Plants, algae, and blue-green bacteria, some prokaryotes, are producers or autotrophs.
F. Only 10% of the Earth’s 40 million species are autotrophs.
G. Other autotrophs use inorganic compounds instead of sunlight to make food; process known as chemosynthesis.
H. Producers make food for themselves and heterotrophs or consumers that cannot make food for themselves.
I. Heterotrophs include animals, fungi, & some bacteria, & protists.
Biochemical Pathways
A. Photosynthesis and cellular respiration are biochemical pathways.
B. Biochemical pathways are a series of reactions where the product of one reaction is the reactant of the next.
C. Only autotrophs are capable of photosynthesis.
D. Both autotrophs & heterotrophs perform cellular respiration to release energy to do work.
E. In photosynthesis, CO2(carbon dioxide) and H2O (water) are combined to form C6H12O6 (glucose) & O2 (oxygen)
6CO2 + 6H2O + energy --> 6O2 + C6H12O6
F. In cellular respiration, O2 (oxygen) is used to burn C6H12O6 (glucose) & release CO2(carbon dioxide), H2O (water), and energy.
G. Usable energy released in cellular respiration is called adenosine triphosphate or ATP.
Light Absorption in Chloroplasts
Chloroplasts in plant & algal cells absorb light energy from the sun during the light dependent reactions. Photosynthetic cells may have thousands of chloroplasts. Chloroplasts from higher plants are surrounded by a double membrane system consisting of an outer and inner envelope and also contain complex internal membrane system is Thylakoid membrane, contain distinct regions. Some thylakoid regions (grana thylakoids) are organized into grana stacks of appressed membranes, whereas others (stromal thylakoids) are unstacked and thus are exposed to the surrounding fluid medium, the chloroplast stroma. Light-capturing pigments in the grana are organized into photosystems The thylakoid membranes are all interconnected and enclose an internal space known as the Lumen.
Pigments
A. Light travels as waves & packets called photons.
B. Wavelength of light is the distance between 2 consecutive peaks or troughs.
C. Sunlight or white light is made of different wavelengths or colors carrying different amounts of energy.
D. A prism separates white light into 7 colors (red, orange, yellow, green, blue, indigo, & violet) ROY G. BIV.
E. These colors are called the visible spectrum.
F. When light strikes an object, it is absorbed, transmitted, or reflected.
G. When all colors are absorbed, the object appears black.
H. When all colors are reflected, the object appears white.
I. If only one color is reflected (green), the object appears that color (e.g. Chlorophyll).
Pigments in the Chloroplasts
A. Thylakoids contain a variety of pigments (green red, orange, yellow...).
B. Chlorophyll (C55H70MgN4O6) is the most common pigment in plants & algae.
C. Chlorophyll a & chlorophyll b are the 2 most common types of chlorophyll in autotrophs. D. Chlorophyll absorbs only red, blue, & violet light.
E. Chlorophyll b absorbs colors or light energy NOT absorbed by chlorophyll a.
F. The light energy absorbed by chlorophyll b is transferred to chlorophyll a in the light reactions.
G. Carotenoids are accessory pigments in the thylakoids & include yellow, orange, & red.
The synthesis of organic compounds from inorganic precursors requires energy and reducing power (low potential electrons). For chemotrophic bacteria and living communities dependent on their activity, the ultimate source of this energy is chemical bonds. In nearly all biological systems, the synthesis of organic molecules is driven directly or indirectly by energy source from the sun. The overall process whereby plants, algae and prokaryotes directly use light energy to synthesize organic compounds is called Photosynthesis.In addition to providing food, biomass, and fossil fuels, photosynthesis in plants produces as a by- product the oxygen required for respiratory activity by all multicellular and many unicellular organisms.
Photosynthesis is encompasses both a series of reaction that involves light absorption, energy conversion, electron transfer and multistep enzymatic pathway that converts CO2 and water into carbohydrates.
6CO2 + 6H2O + energy --> 6O2 + C6H12O6
Photosynthesis is a biological Oxidation-Reduction process. In photosynthetic eukaryote, photosynthesis takes places in the chloroplast. The plant chloroplast is thought to have arisen from the endosymbiosis association of prokaryotic cell and photosynthetic bacterium related to modern cyanobacteria.
Photosynthesis requires the coordination of two phases: light reaction and carbon linked reactions. Light reaction produces O2, ATP and NADPH; and carbon linked reactions which reduceCO2 to carbohydrate and consumes the ATP and NADPH produced in the light reactions.
Light Reaction:
Light has properties of both waves and particles nature. In case of quantum mechanical description, radiant energy is visualized as being a stream of energy carrying particles called quanta. Each quantum of light is equal to a single photon is equal to Planck's constant h (6.626X10-34 Joules. Sec). Oxygenic Photosynthetic organisms use visible light, with wave lengths of 400 to 700nm.
For light energy to be used by any system, the light must first be absorbed. The light absorbing molecules called as Pigments. The absorbing photons by pigment molecules results in the conversion of the pigment its lowest energy state to an excited state.
Almost all photosynthetic organisms contain chlorophyll or related pigments. Plants, Cyanobacteria and Algae synthesize chlorophyll, whereas anaerobic photosynthetic bacteria produce a molecular variant called Bacteriochlorophyll. The first committed precursor in the biosynthesis of chlorophyll and heme is Delta –Aminolevulinic Acid, it produces from glutamate.
Carotenoids participate in light absorption and photo protection. This class of molecules includes carotenes, which conjugated double bond system of carbon and hydrogen and the xanthophyll, which in addition contain oxygen atoms in their terminal ring. Like carotenoids, other accessory pigments that absorb green light, those are Phycobillins. The initial energy transformations in photosynthesis takes place at specific sites in the photosynthetic integral membrane protein complexes called Reaction Centres. Reaction centres contain both special chlorophyll and electron acceptor molecules involved in energy conversion. Oxygenic Photosynthetic organisms contain two photochemical reaction centres, PSI and PSII. A photosystem contain a photochemical reaction centre and multiple antennae (axillary light harvesting pigment-protein complexes). These antennae function to absorb light energy, transferring it to the reaction centre, where the energy is then converted into stable chemical products. Most of the oxygenic photosynthetic organisms contain chlorophyll a/b proteins as their principal antennae. Protien complexes of the thylakoid membrane exhibit lateral homogeneity. Two types of integral membranes proteins are present in the chloroplast: stacked or appressed (granal membranes) and expose or unstacked membranes known as stromal membranes. Ex: ATP Synthase is located almost entirely in the stromal exposed membranes, plastocyanin are distributed unequally in granal membrane and stromal region of the continuous thylakoid lumen. This phenomenon called lateral heterogeneity indicates that two photosystems, which cooperate in transferring electrons from water to NADP+ in electron transport chain. Phosphorylation of Light Harvesting Complex II (LHC-II) may influence the distribution of energy between PSI and PSII.
An electron transport pathway in chloroplast a membrane produces O2, NADPH and ATP and involves the cooperation of PSI and PSII.
Photosystem I(PSI):
PSI is driven by light of wave length 700nm or less. In PSI, the photochemical reaction centre is designated as P700 because it absorbs wavelength maximum at 700nm and found almost in stroma lamellae and the edges of grana lamellae.
Photosystem II (PSII):
PSII is driven by light of wavelength shorter than 690nm and it absorption maxima is light of wavelength 680nm. PSII is located predominantly grana lamellae. In addition to that some protein complexes are involved in charges separation in electron transport pathway. Two proteins D1 and D2, bind electrons transfer prosthetic group such as P680, pheophytin and plastoquinone and CP43, CP47.
Oxidation of water produces O2 and releases electrons required by PSII. The photolysis of water reaction required manganese and other cofactors. The cytochrome b6f complex transfer electrons from reduced plastoquinone to oxidized plastocyanin. This b6f complex is similar structure and function to the cytochrome bc1 complex (complex III) of the mitochondrial respiratory chain. Proton translocati6n via cytochrome b6f is thought to involve a Q- cycle. According to this model, the cytochrome complexes contain one quinol-binding site, and one Quinone binding site present in opposite side of the membrane. Quinol oxidation proceeds in two discrete steps located at luminal side of the membrane. Quinol is oxidized to the semi quinone by the Reiske –S centre and the released electron passes from the Fe-S centre to cytochrome f, then on to plastocyanin. Plastocyanin, soluble protein, links cytochrome b6f and PSI. Plastocyanin is electron carrier, low molecular mass copper containing molecule. In algae and cyanobacteria the biosynthesis of plastocyanin is depending upon the availability of copper in growth medium. In the absence of copper, these cells are unable to produce plastocyanin and instead synthesize C-type cytochrome; Cyt-553 which isfunctionally interchangeable with plastocyanin. PSI functions as a light dependent plastocyanin-ferridoxin oxidoreductase. PSI contains approximately 15 protein subunits. PsaA and PsaB are involved in binding the major electron transfer carriers, such as P700, the chlorophyll a acceptor molecule (A0), phylloquinone (vitamin k) and the bound Fe-S centre Fx .
The light dependent plastocyanin- ferridoxin oxidoreductase generates reduced ferridoxin and capable to produced NADP+ in thermodynamically favourable reaction in the physiological pH. Electrons from PSI are transferred to NADP+ in the stroma in a reaction requiring ferridoxin and ferridoxin-NADP+ reductase. The intermediate enzyme called ferridoxin-NADP+ reductase (FNR) is an FAD containing enzymes that can be reduced in two single electron steps. The first electron reduces FNR to the flavin semi quinone state and second step is to the fully reduced state FADH2. FNR is loosely associated with thylakoid membrane and easily dissociated.
Electron transport and ATP synthesis are coupled in vivo. A major feature of both oxidative phosphorylation and photophosphorylation coupled to electron transport. Value for noncyclic photophosphorylation in chloroplasts are generally in the range of 1.0 to1.5 ATP molecules synthesized from ADP and Pi for every electrons transferred from water to NADP+. Chloroplasts synthesize ATP by a chemiosmotic mechanism driven by a proton gradient. Experimental manipulation of luminal and stromal pH can promote light dependent ADP phosphorylation in chloroplasts. The structural resolution of the F1-F0 complex from mitochondrial ATP synthase provides insights in to the coupling of proton transport and ATP synthesis.
Dark Reaction:
The Calvin Cycle is also known as Reductive Pentose Phosphate Pathway, is series of biochemical reactions taking place in the stroma of chloroplast of eukaryotic photosynthetic organisms (prokaryotic cytosol organism). It was discovered by Melvin Calvin and Andy Benson at the University of California, Berkeley.
Reduction and regeneration of intermediates follow the first CO2 fixation reaction. In C3 plants, photosynthetic carbon fixation is catalysed by a single enzyme Rubisco. Most of the plants produced three carbon compounds, 3-phosphoglycerate (3-PGA) as the first stable product in the multistep conversion of CO2 into carbohydrate. This functionally defriended group, which includes most crop plants, is referred as C3 plants. The researcher used a kinetic approach, applying 14CO2 to cell suspensions of the green algae Chlorella and Scenedesmus and taking samples at short intervals to identify the radiolabeled compounds produced over time.
Rubisco play critical role in thebiochemistry of the chloroplast. It is most abundant soluble protein in the chloroplast and possibly one of the most abundant in the biosphere. Rubisco is consist of eight large subunits (56kDa) and eight small (14kDa) subunits called L and respectively. The role of S subunit function is less clear. In most eukaryotes, L subunits are encoded by the chloroplast genome and S subunits by the nuclear genome.The latter are transport into the chloroplast, where they combine with the larger subunit in the chloroplast stroma to yield an active holoenzyme.
The Calvin Cycle is regulated by light via changes in pH and Mg+2 concentrations. Many of the Calvin cycle enzymes are catalyse reversible reactions (eg: aldolase, transketolase, glyceraldehyde 3-phoshate dehydrogenase) are common to the glycolytic pathway for carbohydrate degradation.
Changes in stromal pH and Mg+2 concentration are important regulators of enzymes such as Rubis co, fructose 1,6 bisphoshatase and phosphoribulokinase. Rubisco activation involves the formation of Carbamate –Mg+2complexes on a specific lysine at the active site.
Light linked covalent modification is important regulating the Calvin Cycle. Rubisco also functions as an oxygenase. Rubisco catalyses the reaction of O2 with ribulose1,5 biphoshate, producing 3-PGA and two molecules of 2-phosphoglycolate.
A. All organisms require energy.
B. Some organisms (autotrophs) obtain energy directly from the sun and store it in organic compounds (glucose) during a process called photosynthesis.
6CO2 + 6H2O + energy --> 6O2 + C6H12O6
Energy for Life Processes
A. Energy is the ability to do work.
B. Work for a cell includes growth & repair, active transport across cell membranes, reproduction, synthesis of cellular products, etc.
C. Work is the ability to change or move matter against other forces (W = F x D).
D. Autotrophs or producers convert sunlight, CO2, and H2O into glucose (their food).
E. Plants, algae, and blue-green bacteria, some prokaryotes, are producers or autotrophs.
F. Only 10% of the Earth’s 40 million species are autotrophs.
G. Other autotrophs use inorganic compounds instead of sunlight to make food; process known as chemosynthesis.
H. Producers make food for themselves and heterotrophs or consumers that cannot make food for themselves.
I. Heterotrophs include animals, fungi, & some bacteria, & protists.
Biochemical Pathways
A. Photosynthesis and cellular respiration are biochemical pathways.
B. Biochemical pathways are a series of reactions where the product of one reaction is the reactant of the next.
C. Only autotrophs are capable of photosynthesis.
D. Both autotrophs & heterotrophs perform cellular respiration to release energy to do work.
E. In photosynthesis, CO2(carbon dioxide) and H2O (water) are combined to form C6H12O6 (glucose) & O2 (oxygen)
6CO2 + 6H2O + energy --> 6O2 + C6H12O6
F. In cellular respiration, O2 (oxygen) is used to burn C6H12O6 (glucose) & release CO2(carbon dioxide), H2O (water), and energy.
G. Usable energy released in cellular respiration is called adenosine triphosphate or ATP.
Light Absorption in Chloroplasts
Chloroplasts in plant & algal cells absorb light energy from the sun during the light dependent reactions. Photosynthetic cells may have thousands of chloroplasts. Chloroplasts from higher plants are surrounded by a double membrane system consisting of an outer and inner envelope and also contain complex internal membrane system is Thylakoid membrane, contain distinct regions. Some thylakoid regions (grana thylakoids) are organized into grana stacks of appressed membranes, whereas others (stromal thylakoids) are unstacked and thus are exposed to the surrounding fluid medium, the chloroplast stroma. Light-capturing pigments in the grana are organized into photosystems The thylakoid membranes are all interconnected and enclose an internal space known as the Lumen.
Pigments
A. Light travels as waves & packets called photons.
B. Wavelength of light is the distance between 2 consecutive peaks or troughs.
C. Sunlight or white light is made of different wavelengths or colors carrying different amounts of energy.
D. A prism separates white light into 7 colors (red, orange, yellow, green, blue, indigo, & violet) ROY G. BIV.
E. These colors are called the visible spectrum.
F. When light strikes an object, it is absorbed, transmitted, or reflected.
G. When all colors are absorbed, the object appears black.
H. When all colors are reflected, the object appears white.
I. If only one color is reflected (green), the object appears that color (e.g. Chlorophyll).
Pigments in the Chloroplasts
A. Thylakoids contain a variety of pigments (green red, orange, yellow...).
B. Chlorophyll (C55H70MgN4O6) is the most common pigment in plants & algae.
C. Chlorophyll a & chlorophyll b are the 2 most common types of chlorophyll in autotrophs. D. Chlorophyll absorbs only red, blue, & violet light.
E. Chlorophyll b absorbs colors or light energy NOT absorbed by chlorophyll a.
F. The light energy absorbed by chlorophyll b is transferred to chlorophyll a in the light reactions.
G. Carotenoids are accessory pigments in the thylakoids & include yellow, orange, & red.
The synthesis of organic compounds from inorganic precursors requires energy and reducing power (low potential electrons). For chemotrophic bacteria and living communities dependent on their activity, the ultimate source of this energy is chemical bonds. In nearly all biological systems, the synthesis of organic molecules is driven directly or indirectly by energy source from the sun. The overall process whereby plants, algae and prokaryotes directly use light energy to synthesize organic compounds is called Photosynthesis.In addition to providing food, biomass, and fossil fuels, photosynthesis in plants produces as a by- product the oxygen required for respiratory activity by all multicellular and many unicellular organisms.
Photosynthesis is encompasses both a series of reaction that involves light absorption, energy conversion, electron transfer and multistep enzymatic pathway that converts CO2 and water into carbohydrates.
6CO2 + 6H2O + energy --> 6O2 + C6H12O6
Photosynthesis is a biological Oxidation-Reduction process. In photosynthetic eukaryote, photosynthesis takes places in the chloroplast. The plant chloroplast is thought to have arisen from the endosymbiosis association of prokaryotic cell and photosynthetic bacterium related to modern cyanobacteria.
Photosynthesis requires the coordination of two phases: light reaction and carbon linked reactions. Light reaction produces O2, ATP and NADPH; and carbon linked reactions which reduceCO2 to carbohydrate and consumes the ATP and NADPH produced in the light reactions.
Light Reaction:
Light has properties of both waves and particles nature. In case of quantum mechanical description, radiant energy is visualized as being a stream of energy carrying particles called quanta. Each quantum of light is equal to a single photon is equal to Planck's constant h (6.626X10-34 Joules. Sec). Oxygenic Photosynthetic organisms use visible light, with wave lengths of 400 to 700nm.
For light energy to be used by any system, the light must first be absorbed. The light absorbing molecules called as Pigments. The absorbing photons by pigment molecules results in the conversion of the pigment its lowest energy state to an excited state.
Almost all photosynthetic organisms contain chlorophyll or related pigments. Plants, Cyanobacteria and Algae synthesize chlorophyll, whereas anaerobic photosynthetic bacteria produce a molecular variant called Bacteriochlorophyll. The first committed precursor in the biosynthesis of chlorophyll and heme is Delta –Aminolevulinic Acid, it produces from glutamate.
Carotenoids participate in light absorption and photo protection. This class of molecules includes carotenes, which conjugated double bond system of carbon and hydrogen and the xanthophyll, which in addition contain oxygen atoms in their terminal ring. Like carotenoids, other accessory pigments that absorb green light, those are Phycobillins. The initial energy transformations in photosynthesis takes place at specific sites in the photosynthetic integral membrane protein complexes called Reaction Centres. Reaction centres contain both special chlorophyll and electron acceptor molecules involved in energy conversion. Oxygenic Photosynthetic organisms contain two photochemical reaction centres, PSI and PSII. A photosystem contain a photochemical reaction centre and multiple antennae (axillary light harvesting pigment-protein complexes). These antennae function to absorb light energy, transferring it to the reaction centre, where the energy is then converted into stable chemical products. Most of the oxygenic photosynthetic organisms contain chlorophyll a/b proteins as their principal antennae. Protien complexes of the thylakoid membrane exhibit lateral homogeneity. Two types of integral membranes proteins are present in the chloroplast: stacked or appressed (granal membranes) and expose or unstacked membranes known as stromal membranes. Ex: ATP Synthase is located almost entirely in the stromal exposed membranes, plastocyanin are distributed unequally in granal membrane and stromal region of the continuous thylakoid lumen. This phenomenon called lateral heterogeneity indicates that two photosystems, which cooperate in transferring electrons from water to NADP+ in electron transport chain. Phosphorylation of Light Harvesting Complex II (LHC-II) may influence the distribution of energy between PSI and PSII.
An electron transport pathway in chloroplast a membrane produces O2, NADPH and ATP and involves the cooperation of PSI and PSII.
Photosystem I(PSI):
PSI is driven by light of wave length 700nm or less. In PSI, the photochemical reaction centre is designated as P700 because it absorbs wavelength maximum at 700nm and found almost in stroma lamellae and the edges of grana lamellae.
Photosystem II (PSII):
PSII is driven by light of wavelength shorter than 690nm and it absorption maxima is light of wavelength 680nm. PSII is located predominantly grana lamellae. In addition to that some protein complexes are involved in charges separation in electron transport pathway. Two proteins D1 and D2, bind electrons transfer prosthetic group such as P680, pheophytin and plastoquinone and CP43, CP47.
Oxidation of water produces O2 and releases electrons required by PSII. The photolysis of water reaction required manganese and other cofactors. The cytochrome b6f complex transfer electrons from reduced plastoquinone to oxidized plastocyanin. This b6f complex is similar structure and function to the cytochrome bc1 complex (complex III) of the mitochondrial respiratory chain. Proton translocati6n via cytochrome b6f is thought to involve a Q- cycle. According to this model, the cytochrome complexes contain one quinol-binding site, and one Quinone binding site present in opposite side of the membrane. Quinol oxidation proceeds in two discrete steps located at luminal side of the membrane. Quinol is oxidized to the semi quinone by the Reiske –S centre and the released electron passes from the Fe-S centre to cytochrome f, then on to plastocyanin. Plastocyanin, soluble protein, links cytochrome b6f and PSI. Plastocyanin is electron carrier, low molecular mass copper containing molecule. In algae and cyanobacteria the biosynthesis of plastocyanin is depending upon the availability of copper in growth medium. In the absence of copper, these cells are unable to produce plastocyanin and instead synthesize C-type cytochrome; Cyt-553 which isfunctionally interchangeable with plastocyanin. PSI functions as a light dependent plastocyanin-ferridoxin oxidoreductase. PSI contains approximately 15 protein subunits. PsaA and PsaB are involved in binding the major electron transfer carriers, such as P700, the chlorophyll a acceptor molecule (A0), phylloquinone (vitamin k) and the bound Fe-S centre Fx .
The light dependent plastocyanin- ferridoxin oxidoreductase generates reduced ferridoxin and capable to produced NADP+ in thermodynamically favourable reaction in the physiological pH. Electrons from PSI are transferred to NADP+ in the stroma in a reaction requiring ferridoxin and ferridoxin-NADP+ reductase. The intermediate enzyme called ferridoxin-NADP+ reductase (FNR) is an FAD containing enzymes that can be reduced in two single electron steps. The first electron reduces FNR to the flavin semi quinone state and second step is to the fully reduced state FADH2. FNR is loosely associated with thylakoid membrane and easily dissociated.
Electron transport and ATP synthesis are coupled in vivo. A major feature of both oxidative phosphorylation and photophosphorylation coupled to electron transport. Value for noncyclic photophosphorylation in chloroplasts are generally in the range of 1.0 to1.5 ATP molecules synthesized from ADP and Pi for every electrons transferred from water to NADP+. Chloroplasts synthesize ATP by a chemiosmotic mechanism driven by a proton gradient. Experimental manipulation of luminal and stromal pH can promote light dependent ADP phosphorylation in chloroplasts. The structural resolution of the F1-F0 complex from mitochondrial ATP synthase provides insights in to the coupling of proton transport and ATP synthesis.
Dark Reaction:
The Calvin Cycle is also known as Reductive Pentose Phosphate Pathway, is series of biochemical reactions taking place in the stroma of chloroplast of eukaryotic photosynthetic organisms (prokaryotic cytosol organism). It was discovered by Melvin Calvin and Andy Benson at the University of California, Berkeley.
Reduction and regeneration of intermediates follow the first CO2 fixation reaction. In C3 plants, photosynthetic carbon fixation is catalysed by a single enzyme Rubisco. Most of the plants produced three carbon compounds, 3-phosphoglycerate (3-PGA) as the first stable product in the multistep conversion of CO2 into carbohydrate. This functionally defriended group, which includes most crop plants, is referred as C3 plants. The researcher used a kinetic approach, applying 14CO2 to cell suspensions of the green algae Chlorella and Scenedesmus and taking samples at short intervals to identify the radiolabeled compounds produced over time.
Rubisco play critical role in thebiochemistry of the chloroplast. It is most abundant soluble protein in the chloroplast and possibly one of the most abundant in the biosphere. Rubisco is consist of eight large subunits (56kDa) and eight small (14kDa) subunits called L and respectively. The role of S subunit function is less clear. In most eukaryotes, L subunits are encoded by the chloroplast genome and S subunits by the nuclear genome.The latter are transport into the chloroplast, where they combine with the larger subunit in the chloroplast stroma to yield an active holoenzyme.
The Calvin Cycle is regulated by light via changes in pH and Mg+2 concentrations. Many of the Calvin cycle enzymes are catalyse reversible reactions (eg: aldolase, transketolase, glyceraldehyde 3-phoshate dehydrogenase) are common to the glycolytic pathway for carbohydrate degradation.
Changes in stromal pH and Mg+2 concentration are important regulators of enzymes such as Rubis co, fructose 1,6 bisphoshatase and phosphoribulokinase. Rubisco activation involves the formation of Carbamate –Mg+2complexes on a specific lysine at the active site.
Light linked covalent modification is important regulating the Calvin Cycle. Rubisco also functions as an oxygenase. Rubisco catalyses the reaction of O2 with ribulose1,5 biphoshate, producing 3-PGA and two molecules of 2-phosphoglycolate.
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