What happens during regeneration phase in photosynthesis
During the regeneration phase of photosynthesis, the energy that was captured and stored during the light-dependent reactions is used to convert ADP (adenosine diphosphate) back into ATP (adenosine triphosphate), and NADP+ (nicotinamide adenine dinucleotide phosphate) back into NADPH. This phase takes place in the stroma of the chloroplasts.
The ATP and NADPH are then used to convert carbon dioxide (CO2) molecules into glucose, a process known as the Calvin cycle or the dark reactions. This phase involves a series of enzyme-catalyzed reactions, such as carbon fixation, reduction, and regeneration of RuBP (ribulose-1,5-bisphosphate). The ATP and NADPH provide the energy and reducing power needed for these reactions.
The glucose produced during the regeneration phase can be used for immediate energy needs or stored as starch for later use. Additionally, the glucose can be converted into other organic molecules, such as carbohydrates, lipids, and proteins, to support plant growth and development.
During the regeneration phase in photosynthesis, several crucial events occur. Here are the steps involved:
1. In the first step after the light-dependent reactions, ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate) are utilized by specific enzymes to convert carbon dioxide (CO2) into glucose molecules – a process called carbon fixation.
2. The Calvin cycle, also known as the dark reaction or light-independent reaction, takes place. It occurs in the stroma of chloroplasts. In this phase, the ATP and NADPH generated in the light-dependent reactions are utilized to reduce CO2 and build glucose molecules.
3. The carbon fixation process starts with the enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzing the reaction between CO2 and the 5-carbon sugar RuBP (ribulose-1,5-bisphosphate) to form a 6-carbon intermediate. This intermediate is highly unstable and quickly breaks down into two molecules of 3-phosphoglycerate (3-PGA).
4. ATP plays a significant role in phosphorylating (adding phosphate groups) to the 3-PGA molecules, forming 1,3-bisphosphoglycerate (1,3-BPG).
5. Next, NADPH donates electrons to 1,3-BPG, which leads to the conversion of 1,3-BPG into glyceraldehyde 3-phosphate (G3P). Some of the G3P molecules are used to synthesize glucose, while the remaining G3P molecules continue through the Calvin cycle to regenerate the RuBP molecule.
6. Five out of every six G3P molecules formed are necessary to regenerate RuBP by rearranging the carbon skeletons through several enzymatic reactions. This regeneration requires ATP from the light-dependent reactions to convert G3P back into RuBP.
7. The final step involves the release of one G3P molecule, while the remaining RuBP molecules continue the cycle by reacting with CO2. This continuous regeneration process enables the Calvin cycle to sustain itself and continue fixing more carbon dioxide molecules.
Overall, the regeneration phase of photosynthesis ensures the continuation of the Calvin cycle, allowing the plants to produce glucose and other organic compounds necessary for growth and energy production.