Give systematic re of calvin cycle?
Answers
The Calvin cycle is the cycle of chemical reactions performed by plants to “fix” carbon from CO2 into three-carbon sugars.Later, plants and animals can turn these three-carbon compounds into amino acids, nucleotides, and more complex sugars such as starches.
This process of “carbon fixation” is how most new organic matter is created. The sugars created in the Calvin cycle are also used by plants for long-term energy storage, unlike ATP which is used up quickly after it is created.
These plant sugars can also become a source of energy for animals who eat the plants, and predators who eat those herbivores.
The Calvin cycle is also sometimes referred to as the “light independent” reactions of photosynthesis, since it is not powered directly by photons from the Sun. Instead, the Calvin cycle is powered by ATP and NADPH, which are created by harnessing the energy from photons in the light-dependent reactions.
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Calvin Cycle Steps
Carbon Fixation
In carbon fixation, a CO2 molecule from the atmosphere combines with a five-carbon acceptor molecule called ribulose-1,5-bisphosphate (RuBP).
The resulting six-carbon compound is then split into two molecules of the three-carbon compound, 3-phosphoglyceric acid (3-PGA).
This reaction is catalyzed by the enzyme RuBP carboxylase/oxygenase, also known as RuBisCO. Due to the key role it plays in photosynthesis, RuBisCo is probably the most abundant enzyme on Earth.
Reduction
In the second stage of the Calvin cycle, the 3-PGA molecules created through carbon fixation are converted into molecules of a simple sugar – glyceraldehyde-3 phosphate (G3P).
This stage uses energy from ATP and NADPH created in the light-dependent reactions of photosynthesis. In this way, the Calvin cycle becomes the way in which plants convert energy from sunlight into long-term storage molecules, such as sugars. The energy from the ATP and NADPH is transferred to the sugars.
This step is called “reduction” because NADPH donates electrons to the 3-phosphoglyceric acid molecules to create glyceraldehyde-3 phosphate. In chemistry, the process of donating electrons is called “reduction,” while the process of taking electrons is called “oxidation.”
Regeneration
Some glyceraldehyde-3 phosphate molecules go to make glucose, while others must be recycled to regenerate the five-carbon RuBP compound that is used to accept new carbon molecules.
The regeneration process requires ATP. It is a complex process involving many steps.
Because it takes six carbon molecules to make a glucose, this cycle must be repeated six times to make a single molecule of glucose.
To accomplish this equation, five out of six glyceraldehyde-3 phosphate molecules that are created through the Calvin cycle are regenerated to form RuBP molecules. The sixth exits the cycle to become one half of a glucose molecule.
Calvin Cycle Diagram
Each turn of the Calvin cycle “fixes” one molecule of carbon that can be used to make sugar.
It takes three turns of the Calvin cycle to create one molecule of glyceraldehyde-3 phosphate.
After six turns of the Calvin cycle, two molecules of glyceraldehyde-3 phosphate can be combined to make a glucose molecule.
Each turn of the Calvin cycle also uses up 3 ATP and 2 NADPH in the processes of reducing (adding electrons to) 3-phosphoglyceric acid to produce glyceraldehyde-3 phosphate, and regenerating RuBP so that they can accept a new atom of carbon from CO2 from the air.
This means that to produce a single molecule of glucose, 18 ATP and 12 NADPH are consumed
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