light reaction

• The products of Light Reactions are the ATP and NADPH.
• The products of Light Reactions are excreted or produced in the stroma of the chloroplast.
• The plant makes glucose from ATP and NADPH through the Light Independent Reactions, Dark Reactions, and Calvin Cycle.
• In the Light Independent Reactions, carbon dioxide enters the interior of a leaf via pores called stomata and diffuses into the stroma of the chloroplast where sugar is synthesized, not directly driven by light.
• In the Dark Reactions, carbon atoms from CO2 are fixed (incorporated into organic molecules) and used to build three-carbon sugars, fueled by ATP and NADPH from the light reactions.
• In the Calvin Cycle, an enzyme nicknamed Rubisco (RuBP carboxylase-oxygenase) catalyzes attachment of CO2 to a five-carbon sugar called ribulose bisphosphate (RuBP), resulting in the formation of a six-carbon molecule that splits into two molecules of a three-carbon compound called 3-phosphoglycerate (3-PGA).
• In the Reduction of 3-PGA into G3P, each molecule of 3-PGA receives a phosphate group from ATP, turning into a doubly phosphorylated molecule called 1,3-bisphosphoglycerate and leaving behind ADP as a by-product.
• In the Reduction of 3-PGA into G3P, each molecule of 1,3-bisphosphoglycerate is reduced, receiving two electrons from NADPH and losing one of its phosphate groups, turning into a three-carbon sugar called glyceraldehyde 3-phosphate (G3P), producing NADP and phosphate as by-products.
• In the Regeneration of RuBP, one of the 6 G3P molecules goes on to form glucose while the rest (5) of the G3P molecules are used to regenerate the RuBP, requiring three more molecules of ATP.
• The Calvin Cycle requires three turns to produce one G3P molecule that can exit the cycle and go towards making glucose.
• Plants that follow the Calvin/C3 pathway to fix carbon are called C3 plants, which involve adding carbon dioxide to RuBP to form a three-carbon compound G3P.
• Photorespiration is a process in plant metabolism in which the key enzyme RuBisCo, responsible for the fixing of carbon dioxide, reacts with oxygen rather than carbon dioxide.
• At night, CAM plants open their stomata, allowing CO2 to diffuse into the leaves and is fixed into oxaloacetate by PEP carboxylase, then converted to malate or another type of organic acid.
• NADPH 6 NADPH are converted to 6 NADP (during the reduction step).
• In the daylight, CAM plants do not open their stomata, but they can still photosynthesize because the organic acids are transported out of the vacuole and broken down to release CO2, which enters the Calvin cycle.
• A G3P molecule contains three fixed carbon atoms, so it takes two G3Ps to build a six-carbon glucose molecule.
• CAM plants separate the light-dependent reactions and the use of CO2 in the Calvin cycle in space, instead of separating these processes in time.
• 5 G3P molecules are recycled, regenerating 3 RuBP acceptor molecules.
• The light-dependent reactions and the Calvin cycle are physically separated in C4 plants, with the light-dependent reactions occurring in the mesophyll cells and the Calvin cycle occurring in bundle-sheath cells.
• The organic acid is stored inside vacuoles until the next day.
• 1 G3P molecule exits the cycle and goes towards making glucose.
• In three turns of the Calvin Cycle, carbon 3CO2 combine with 3 RuBP acceptors, making 6 molecules of glyceraldehyde-3-phosphate (G3P).
• ATP 9 ATP are converted to 9 ADP (6 during the fixation step, 3 during the regeneration step).
• It would take six turns of the cycle, or 6 CO2, 18 ATP, and 12 NADPH, to produce one molecule of glucose.