Calvin Cycle

• The metabolism of stonecrop plant, Crassulaceae family, mainly includes succulents.
• Cactus is a CAM plant.
• The major features and chemical events in photosynthesis include the initial incorporation of carbon into a larger organic molecule, known as carbon fixation, which is catalysed by the enzyme rubisco.
• The initial incorporation of carbon into a larger organic molecule, known as carbon fixation, produces a six-carbon molecule that quickly breaks down into 3-phosphoglycerate (3-PGA) molecules, which is why the Calvin cycle is often referred to as the C3 pathway.
• The process of photosynthesis requires two molecules of ATP for the initial incorporation of carbon into a larger organic molecule, known as carbon fixation, which is catalysed by the enzyme rubisco.
• Malate is then broken down forming the -carbon molecule pyruvate and releases CO2.
• PGAL is a substance used by plants to make other organic substances, such as glucose.
• The ATP and NADPH synthesized during light reactions are dissolved in the stroma.
• Using an extra ATP, C4 plants are able to convert pyruvate back into PEP permitting the cycle to continue.
• A typical example of a C4 plant is corn.
• In the C4 pathway, mesophyll cells capture more CO2 using PEP (phosphoenolpyruvate) carboxylase.
• The three turns of the Calvin cycle use up 9 molecules of ATP (2 ATP molecules in every Carbon fixation and 1 ATP in every synthesis of G3P) and 6 molecules of NADPH (2 NADPH molecules in every synthesis of G3P).
• Crassulacean acid metabolism (CAM) is an adaptation to dry or xeric conditions in some plants, where carbon is captured and sugar is synthesized in the same mesophyll cells at different times of the day.
• There are alternative pathways for carbon fixation: the C4 pathway and Crassulacean acid metabolism (CAM).
• Unlike many plants, Cam plants open their stomata at night allowing CO2 to diffuse in the mesophyll cells while minimizing water loss.
• The Calvin cycle was named after Melvin Calvin who explained in detail the steps of this cycle in the 1940s.
• At daytime, CAM plants close their stomata to reduce evapotranspiration.
• PEP carboxylase (3 carbons) binds to CO2 to make oxaloacetic acid (OAA), a 4 carbon molecule.
• The OAA is quickly converted into malate (4 carbons).
• Photorespiration is a series of reactions that start when the rubisco enzyme adds O2 rather than CO2 to RuBP, preventing the Calvin cycle from synthesizing sugar, reducing photosynthetic efficiency, and wasting ATP and NADPH.