calvin cycle

• The Calvin Cycle, also known as dark reaction, light-independent reaction, Calvin cycle, or c3 cycle, was discovered by Melvin Calvin and Andrew Benson.
• The process of photosynthesis requires six turns of the light reactions to produce two photons which will make one glucose.
• The Calvin Cycle is a biochemical pathway that allows for carbon fixation, incorporating CO2 into organic molecules.
• The Calvin Cycle occurs in the stroma and uses ATP and NADPH from light-dependent reactions.
• The sugar produced in the Calvin Cycle is a three-carbon sugar known as G3P or glyceraldehyde-3-phosphate.
• The Calvin Cycle needs to ‘spin’ three times to make one molecule of G3P from three molecules of CO2.
• To build up carbohydrates, cells need carbon and oxygen atoms from CO2, hydrogen atoms provided by NADPH from photosystem II, and energy provided by ATP from ETC of light-dependent reactions.
• Carbon fixation is a process of incorporating an inorganic carbon molecule, CO2, into an organic material.
• Carbon from the atmosphere is “fixed” into carbohydrates in the Calvin Cycle.
• In the first step of the Calvin Cycle, the CO2 molecule is attached to a five-carbon sugar molecule named ribulose biphosphate (RuBP) aided by an enzyme named rubisco or RuBP carboxylase.
• Rubisco is believed to be the most abundant protein in the chloroplast and maybe on Earth.
• The split forms two molecules of a 3-phosphoglycerate (3-carbon).
• In the second step of the Calvin Cycle, PGA molecules are phosphorylated by ATP and reduced by NADPH.
• A phosphate group (from ATP) is then attached to each 3-phosphoglycerate by an enzyme, forming 1,3-phosphoglycerate.
• NADPH swoops in and reduces 1,3-biphosphogycerate to G3P.
• For every six G3Ps produced by the Calvin Cycle, five are recycled to regenerate three molecules of RuBP.
• Only one G3P leaves the cycle to be packaged for use by the cell.
• It will take two molecules of G3P to make one molecule of glucose.
• The ADP and NADP+ that is formed during the Calvin Cycle will be transported back to the thylakoid membrane and will enter the light reactions.
• Here, they will be ‘recharged’ with energy and become ATP and NADPH.
• Add 3 ATP to 3 mol ribulose para maging 3 ADP.
• Glucose can be connected in chains to form starch.
• 3-PGA will have 18 carbons which will undergo phosphorylation with the use of 6 ATP formed during light reactions.
• Two G3Ps can combine together to form either glucose or fructose which are both are six-carbon sugar.
• The phosphoglycerate will undergo phosphorylation with the help of ATP.
• G3Ps can also be used in lipid and protein synthesis.
• This costs the cell another three molecules of ATP, but also provides another set of RuBP to continue the cycle.
• Five molecules of G3P undergo a series of complex enzymatic reactions to form three molecules of RuBP.
• The PGAL set aside needs two PGAL(to synthesize glucose).
• 6 molecules of NADPH.
• The ATP will then go back to the light reaction.
• RuBp is catalyzed by enzyme rubisco (ribulose biphosphate carboxylase oxygenase) in here it is acting as carboxylase will result in 15 carbons.
• The join of rubp and co2 produce 6 molecules (the first stable compound, can't be easily affected).
• 1,3-diphosphoglycerate (P-C-C-C-C-P) has 18 carbons.
• 3 molecules of CO2,
• Ribulose monophosphate can be used to make more RuBP or can be converted into 3 ATP.
• From the 6 mol PGAL, 1 molecule is set aside (1 PGAL has 3 carbon).
• To make one molecule of G3P, the chloroplast needs:
• Glucose and fructose can be combined to form sucrose.
• There will be 5 PGAL left which has 15 carbon (along the process, some will lost inorganic phosphate and become 3 ribulose 5-phosphate or monophosphate molecules with 15 carbon atoms).