PS: Simplified
Dark Reactions
The Calvin Cycle also known as the dark reactions of photosynthesis will be covered.
This cycle utilizes the ATP and NADPH synthesized in the light reactions from the light-dependent reactions taken place inside the thylakoid membrane. This is a multistep process that requires the input of CO2 molecules, to create 9ADP molecules, 6NADP+, and 1G3P molecule which will be used to create glucose sugar C6H12O6. This cycle is conventional as it recycles 5G3P molecules which are reused in the cycle to repeat this process in conjunction with the light dependent reaction. It eseentially throws back the 9ATP gets phosphorylated and 6NADPH gets oxidized into the light-dependent reactions.
Although this cycle may seem hard to grasp, and lots of molecules are being inputed and reformed, by breaking this down and visualizing the structure of each molecule it helps to understand it.
Refer to the image above if any questions about the cycle. The Calvin Cycle can be broken down into three stages, the (1st) Carbon Fixation (2nd) Reduction of 3PGA (3rd) Regeneration of RuBP.
1. First 3CO2 are added one at a time binding each with RuBP with the assistance of the Rubisco enzyme. RuBP for better understanding is a five-carbon sugar with two phosphate groups implying the 1-5 bisphoglycerate, the 1-5 implying the directionality, and bis suffix meaning two. This creates a 6 carbon sugar with two phosphate groups which is heavily unstables and breaks into 2-PGA molecules which is phosglycerate.
2. In stage two the reduction phase 6 ATP molecules made from the light-dependent reaction will be phosphorylated giving up its phosphate group to form bisphosglycerate (it previously had 1 phosphate group). After this 6 NADPH molecules an electron carriers oxidizes its electrons to the 1-3 bisphosglycerate molecule creating 6 G3P.
This part is important since it involves the oxidization of two molecules completely transforming our phosglycerate from a 3 PGA molecule into 6 G3P molecules. One is used a net product, and the other five are thrown back into the cycle into the next stage. The 1 G3P molecule is used to create glucose sugar C6H12O6 as a product of the Calvin Cycle. ADP and NADP+ are a result after the oxidation of each molecule.
3. In this third stage of the Calvin Cycle with the remaining 5 G3P molecules, they become phosphorylated by more ATP molecules, 3 to be exact. This creates a net of 3 RuBP molecules that are ready to bind to 3 CO2 molecules are the start of the cycle. In return this phosphorylates 3 more ATP molecules with a net reaction of 9 ATP molecules, 6 NADPH molecules, and input of 3 CO2 molecules. Thus producing 9 ADP molecules, 6 NADP+ molecules, and 1 G3P molecule as a net result of the Calvin Cycle. Most of these products are thrown back into the light dependent reactions to undergo phosphorylation and reduced from ATP synthase and NADP+ reductase. This last stage is called the regeneration of RuBP setting the cycle up again to continue.
The Calvin Cycle despite being named dark reactions and dependency without light, is still functional on the presence of ATP molecules and NADPH molecules which are formed in the thylakoid membrane with the dependency of light. This shows how closely tied these reactions are dependent they are on each other contributing to photosynthesis on a molecular scale.
