logo

Animation: The Calvin Cycle

by Pearson
16 views
Was this helpful ?
0
The Calvin Cycle During the light reaction, light energy has been stored in the chemical bonds of ATP and NADPH. In the Calvin cycle, this stored energy is used to produce sugar molecules. The Calvin cycle is a complex series of chemical reactions carried out in the stroma. The Calvin cycle begins with carbon fixation. Three molecules of carbon dioxide are added to three molecules of a five-carbon sugar abbreviated RuBP. These molecules are then rearranged to form six molecules called 3-PGA, which have three carbons each. In the next two reactions, products from the light reactions are used to boost the energy of these three-carbon molecules. First, six ATP molecules contribute high-energy phosphate groups, so that each three-carbon molecule receives an additional phosphate group. Six molecules of NADPH are oxidized. providing electrons to six three-carbon compounds. The electrons from NADPH reduce the six three-carbon compounds, creating six high-energy G3P molecules. G3P-- or glyceraldehyde 3- phosphate-- is a sugar, the final product of the Calvin cycle. One of the G3P molecules represents the three carbon dioxide molecules fixed so far. The other five G3Ps are reshuffled to regenerate the original RuBP molecules. To summarize, so far the Calvin Cycle has used the energy from the light reactions to reduce three carbon dioxide molecules and produce one molecule of G3P. Three more carbon dioxide molecules are fixed to form G3P in this same complicated way. To make each G3P, the Calvin Cycle consumes 9 ATP molecules and 6 NADPH molecules. These are regenerated in the light reactions. G3P is the actual final product of the Calvin cycle. The cell can combine two G3Ps to make glucose, which stores the energy that chlorophyll originally captured from the sun.
The Calvin Cycle During the light reaction, light energy has been stored in the chemical bonds of ATP and NADPH. In the Calvin cycle, this stored energy is used to produce sugar molecules. The Calvin cycle is a complex series of chemical reactions carried out in the stroma. The Calvin cycle begins with carbon fixation. Three molecules of carbon dioxide are added to three molecules of a five-carbon sugar abbreviated RuBP. These molecules are then rearranged to form six molecules called 3-PGA, which have three carbons each. In the next two reactions, products from the light reactions are used to boost the energy of these three-carbon molecules. First, six ATP molecules contribute high-energy phosphate groups, so that each three-carbon molecule receives an additional phosphate group. Six molecules of NADPH are oxidized. providing electrons to six three-carbon compounds. The electrons from NADPH reduce the six three-carbon compounds, creating six high-energy G3P molecules. G3P-- or glyceraldehyde 3- phosphate-- is a sugar, the final product of the Calvin cycle. One of the G3P molecules represents the three carbon dioxide molecules fixed so far. The other five G3Ps are reshuffled to regenerate the original RuBP molecules. To summarize, so far the Calvin Cycle has used the energy from the light reactions to reduce three carbon dioxide molecules and produce one molecule of G3P. Three more carbon dioxide molecules are fixed to form G3P in this same complicated way. To make each G3P, the Calvin Cycle consumes 9 ATP molecules and 6 NADPH molecules. These are regenerated in the light reactions. G3P is the actual final product of the Calvin cycle. The cell can combine two G3Ps to make glucose, which stores the energy that chlorophyll originally captured from the sun.