Calvin Cycle Definition
The Calvin cycle is a series of chemical reactions that occur in the chloroplasts of plants and many bacteria as part of the dark reactions or light-independent reactions of photosynthesis. It involves fixing carbon from carbon dioxide into three-carbon sugars.
The function of the Calvin Cycle
The Calvin cycle is a process that occurs in the stroma of chloroplasts during photosynthesis. The primary function of the Calvin cycle is carbon fixation, which is making simple sugars from carbon dioxide and water.
The Calvin cycle reactions fix CO2 from the environment to build carbohydrate molecules using energy carriers formed in the first stage of photosynthesis.
The carbohydrate molecules made will have a backbone of carbon atoms, which are used to create three-carbon sugars that can be used to build other sugars such as glucose, starch, and cellulose that are used by plants as a structural building material.
The Calvin cycle can be organized into three basic stages: fixation, reduction, and regeneration. In the first stage, CO2 is fixed into an organic molecule through a series of reactions catalyzed by an enzyme called RuBisCO.
In the second stage, ATP and NADPH created in the light-dependent reactions of photosynthesis are used to convert 3-PGA molecules created through carbon fixation into molecules of simple sugar – glyceraldehyde-3 phosphate (G3P).
In this way, the Calvin cycle becomes the way in which plants convert energy from sunlight into long-term storage molecules such as sugars.
In the third stage, some G3P molecules are converted back into RuBP so that they can do it all over again while others are put aside to make glucose or other organic compounds.
In summary, the function of the Calvin cycle is to fix CO2 from the environment to build carbohydrate molecules using energy carriers formed in the first stage of photosynthesis.
This process creates three-carbon sugars that can be used to build other sugars such as glucose, starch, and cellulose that are used by plants as a structural building material.
Calvin Cycle Steps
The Calvin cycle is a process that occurs in the stroma of chloroplasts in photosynthetic organisms. It is divided into three stages: fixation, reduction, and regeneration.
During the fixation stage, carbon dioxide (CO2) enters the stroma of the chloroplast and reacts with ribulose bisphosphate (RuBP) to form two molecules of 3-phosphoglycerate (3-PGA). This reaction is catalyzed by an enzyme called RuBisCO.
In the reduction stage, ATP and NADPH produced during the light-dependent reactions are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P). This step requires energy from ATP and electrons from NADPH.
In the regeneration stage, some G3P molecules are used to regenerate RuBP so that the cycle can continue. The remaining G3P molecules can be used to produce glucose or other organic compounds needed by the plant.
It takes six turns of the Calvin cycle to produce one molecule of glucose because each turn produces only one G3P molecule with three carbon atoms. Glucose has six carbon atoms, so six turns are required.
Overall, the Calvin cycle is a crucial process for converting CO2 into organic compounds that can be used by plants as a source of energy and building blocks for growth.
Carbon Fixation
Carbon fixation is the process by which inorganic carbon is converted to organic compounds by living organisms. Photosynthetic organisms, such as plants, use carbon fixation to turn inorganic carbon into organic compounds, such as carbohydrates.
The Calvin cycle is the process that occurs during photosynthesis where carbon fixation takes place. It requires light to complete this segment of the cycle and takes place mainly in the leaf of a green plant, more specifically in the stroma of the chloroplasts.
Carbon fixation also occurs in non-autotrophic pathways. Although no heterotrophs use carbon dioxide in biosynthesis, some carbon dioxide is incorporated into their metabolism.
Pyruvate carboxylase consumes carbon dioxide (as bicarbonate ions) as part of gluconeogenesis, and carbon dioxide is consumed in various anaplerotic reactions. CO2 fixation is catalyzed by enoyl-CoA carboxylases/reductases.
Some carboxylases preferentially bind the lighter carbon stable isotope carbon-12 over the heavier carbon-13. This results in higher ratios of carbon-12 to carbon-13 in plants than in free air and is known as “carbon isotope discrimination”.
Reduction
Reduction is the second stage of the Calvin cycle, which is a series of reactions that occur during photosynthesis in plants. The Calvin cycle can be divided into three stages: carbon fixation, reduction, and regeneration.
During the reduction stage, ATP and NADPH obtained from the light-dependent reactions are used to convert 3-PGA molecules into glyceraldehyde 3-phosphate (G3P). This process involves a reduction reaction because it involves the gain of electrons by 3-PGA.
The Calvin cycle is an important pathway in which plants convert sunlight energy into long-term storage molecules such as sugars. The energy from ATP and NADPH is transferred to G3P molecules during the reduction stage of the Calvin cycle. The final product of the Calvin cycle is glucose, which can be used by plants for energy or stored for later use.
Regeneration
Regeneration is the third stage of the Calvin cycle, which is a series of biochemical redox reactions that take place in the stroma of chloroplasts in photosynthetic organisms. The Calvin cycle can be divided into three stages: carbon fixation, reduction, and regeneration.
In the regeneration stage, some of the glyceraldehyde-3-phosphate (G3P) molecules are used to produce glucose, while others are recycled to regenerate the ribulose bisphosphate (RuBP) acceptor.
During regeneration, one G3P molecule leaves the cycle and goes towards making glucose, while five G3Ps must be recycled to regenerate the RuBP acceptor. It takes six turns of the Calvin cycle to fix six carbon atoms from CO2.
These six turns require energy input from 12 ATP molecules and 12 NADPH molecules in the reduction step and 6 ATP molecules in the regeneration step.
Regeneration is a complex process that requires ATP. ATP is also used in the regeneration of RuBP. The remaining G3P molecules regenerate RuBP, which enables the system to prepare for the carbon fixation step.
Calvin Cycle Diagram
The Calvin cycle is a process that occurs during photosynthesis, where plants use carbon dioxide, ATP, and NADPH to produce glucose. The cycle consists of three stages: carbon fixation, reduction, and regeneration.
During the carbon fixation stage, CO2 is fixed into an organic molecule using the enzyme RuBisCO. This results in the formation of two molecules of 3-phosphoglycerate (3-PGA). During the reduction stage, ATP and NADPH are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P).
Finally, during the regeneration stage, some G3P molecules are used to regenerate RuBP (ribulose-1,5-bisphosphate), which is necessary for the carbon fixation stage to continue.
A diagram of the Calvin cycle shows how three CO2 molecules are fixed into organic molecules during each cycle. This allows one net G3P molecule to be produced per cycle.
Calvin Cycle Products
The Calvin cycle is a series of biochemical redox reactions that take place in the stroma of chloroplasts in photosynthetic organisms. The immediate products of one turn of the Calvin cycle are two glyceraldehyde-3-phosphate (G3P) molecules, three ADP, and two NADP+.
The carbohydrate products of the Calvin cycle are three-carbon sugar phosphate molecules, or “triose phosphates”, namely, glyceraldehyde-3-phosphate (G3P). Generally, the carbohydrate products of the Calvin cycle are triose phosphates (G3P).
The Calvin cycle has three primary stages: carbon fixation stage, reduction stage, and regeneration of the starting molecule.
During carbon fixation, CO2 is fixed into an organic molecule by attaching it to a five-carbon sugar called ribulose bisphosphate (RuBP), which forms a six-carbon intermediate that splits into two 3-phosphoglycerate molecules.
During reduction, ATP and NADPH produced during light-dependent reactions are used to convert 3-phosphoglycerate into G3P. Finally, during the regeneration of RuBP, some G3P is used to regenerate RuBP while others are used to produce glucose.
