LESSON 6: C3 CALVIN's CYCLE
The Light Independent Reactions (Dark Reactions) take place in the stroma of the chloroplast where, with help from the energy supplied by ATP and NADPH produced in the light dependent reaction, carbon dioxide (CO2) is converted to carbohydrates. Carbohydrates are very vital substances for humans that provide sustenance from the fructose in our fruits, to the lactose in our milk, and the glycogen in our bodies that store energy. With consumption of these plants once they have gone through the light dependent reaction, we are able to get the energy we need through cellular respiration and also sustain ourselves. Thus, the C3 Calvin's Cycle proves to be very important. Also, it's main purpose is to fixate carbon and this drastically reduces the amount of harmful CO2 in our atmospheres.
I have summarized the process of the C3 Calvin's Cycle, one of the many light dependent reactions that may occur in plants, in the following 7 steps:
I have summarized the process of the C3 Calvin's Cycle, one of the many light dependent reactions that may occur in plants, in the following 7 steps:
PART 1: CARBON FIXATION
1. CO2 enters the stroma and combines with a 5-C ribulose bisphosphate (RuBP), also known as 1,5-bisphosphate, to form an unstable 6-C compound.
2. This 6-C compound is then broken down into 2 3-C phosphoglycerates (PGA). This is the first product in this specific cycle and thus this specific cycle was named the C3 Calvin's Cycle or C3 photosynthesis.
2. This 6-C compound is then broken down into 2 3-C phosphoglycerates (PGA). This is the first product in this specific cycle and thus this specific cycle was named the C3 Calvin's Cycle or C3 photosynthesis.
PART 2: REDUCTION
3. Next, both PGAs are phosphorylated with an ATP molecules. Like mentioned before, this reaction is much like paying money in the currency of 1 ATP for each PGA to "buy" 1 phosphate for each for a total of 2 ATP spent for 2 phosphates. These phosphate groups are removed from the 2 ATPs and 2 ADP are left over. The products of this reaction are 2 3-C 1,3-bisphosphoglycerate molecules (BPGA).
4. Both BPGAs are then reduced through a reduction reaction by NADPH. Each BPGA receives 1 H from 1 NADPH molecule, forming 2 3-C glyceraldehyde-3-phosphates (G3P) and producing 2 NADP+ as left over products.
5. Some of the G3P molecules then move out of the cycle to synthesize carbohydrates, lipids, and proteins. Since the cycle occurs 6 times and that would eventually produce 12 molecules of G3P, of those 2 G3P are removed from the cycle to synthesize essential organic compounds.
4. Both BPGAs are then reduced through a reduction reaction by NADPH. Each BPGA receives 1 H from 1 NADPH molecule, forming 2 3-C glyceraldehyde-3-phosphates (G3P) and producing 2 NADP+ as left over products.
5. Some of the G3P molecules then move out of the cycle to synthesize carbohydrates, lipids, and proteins. Since the cycle occurs 6 times and that would eventually produce 12 molecules of G3P, of those 2 G3P are removed from the cycle to synthesize essential organic compounds.
PART 3: REGENERATION
6. The rest of the G3P molecules undergo a complicated series of reactions referred to as the "sugar shuffle". This reaction forms a 5-C ribulose monophosphate (RuMP).
7. In the final step of the C3 Calvin's Cycle RuMP is phosphorylated by ATP. Another investment is made and for each RuMP molecule 1 ATP is "spent" to "buy" the phosphate groups and attach it to the molecule. After removing the phosphate group from ATP, what's left is an ADP. This reaction is called phosphorylation. The final product is 1 RuBP which is then recycled 6 times by the Calvin's Cycle in order to produce a sufficient amount of products to get the end results. After 6 cycles, the following is the net reaction of the Calvin's Cycle:
7. In the final step of the C3 Calvin's Cycle RuMP is phosphorylated by ATP. Another investment is made and for each RuMP molecule 1 ATP is "spent" to "buy" the phosphate groups and attach it to the molecule. After removing the phosphate group from ATP, what's left is an ADP. This reaction is called phosphorylation. The final product is 1 RuBP which is then recycled 6 times by the Calvin's Cycle in order to produce a sufficient amount of products to get the end results. After 6 cycles, the following is the net reaction of the Calvin's Cycle: