The main difference between PGA and PGAL is that PGA is an intermediate molecule in the Calvin cycle, whereas PGAL is the end product of the Calvin cycle.
Calvin cycle is a series of chemical reactions that convert carbon dioxide and hydrogen carrier compounds into glucose. This Calvin cycle is present in all photosynthetic eukaryotes and in many photosynthetic bacteria. The Calvin cycle has three basic stages: fixation, reduction, and regeneration. Fixation initiates light-independent reactions, fixing CO2 from an inorganic molecule to an organic molecule. In the second stage, ATP and NADPH are used to reduce 3-PGA into G3P, and then ATP and NADPH are converted to ADP and NADP+, respectively. Finally, the last stage of the Calvin cycle involves the regeneration of RuBP, which enables the system to prepare for more CO2. Moreover, the Calvin cycle takes place in the stroma, which is the inner space of chloroplasts.
Key Areas Covered
1. What is PGA
– Definition, Features, Importance
2. What is PGAL
– Definition, Features, Importance
3. Difference Between PGA and PGAL
– Comparison of Key Differences
Key Terms
PGA, PGAL
What is PGA
PGA is the conjugate acid of 3-phosphoglycerate and is an important intermediate in the Calvin cycle. Another name for PGA is 3-phosphoglyceric acid. In this cycle, carbon dioxide molecules are fixed onto a molecule called ribulose-1,5-bisphosphate(RuBP) by the enzyme rubisco. This results in the formation of a six-carbon molecule that immediately break down into two three-carbon molecules called 3-PGA. These two PGA molecules then undergo a series of enzymatic reactions, finally forming glucose.
PGA is the first stable product of carbon fixation. Without PGA, the carbon dioxide entering the cycle would react with RuBP and break down into smaller molecules which are not useful for the plant’s energy needs. Moreover, PGA can readily be converted into other organic compounds the plant can use to reproduce and grow.
PGA has a high-energy content. This molecule has several high-energy phosphate bonds that can readily break down to release energy. The plants take in this energy to power the rest of the Calvin cycle and produce the organic compounds necessary for growth.
Another function of PGA is its involvement of it in the regulation of the Calvin cycle. When there are higher concentrations of PGA, it signals to the enzymes involved in carbon fixation to slow down or stop their activity. This prevents the building up of excess organic compounds in the plant cell, which is toxic.
PGA is also helpful in the regulation of photorespiration, which is a process that can occur when Rubisco binds to oxygen instead of carbon dioxide. This results in the production of glycolate molecules. This molecule then converts into PGA through a series of enzymatic reactions.
What is PGAL
PGAL (phosphoglycolic acid) is the end product of the Calvin cycle. In fact, it is an important metabolic intermediate in the process of photosynthesis.
PGAL is produced during the first step of the photorespiratory pathway, where two molecules of phosphoglycolate are converted into one molecule of PGAL and one molecule of glycolate. It can then be used in the Calvin cycle to produce glucose, while glycolate is further metabolized through the photorespiratory pathway.
PGAL is a precursor for many important biomolecules, such as glucose, fructose, and sucrose. It can be converted into other important metabolites such as nucleotides, lipids, and amino acids. It also helps maintain the balance of carbon and nitrogen metabolism in plants.
Difference Between PGA and PGAL
Definition
PGA is the conjugate acid of 3-phosphoglycerate and is the end product of the Calvin cycle, while PGA or phosphoglycolic acid is an important metabolic intermediate in the process of photosynthesis.
In the Calvin Cycle
PGA is an intermediate molecule in the Calvin cycle, whereas PGAL is the end product of the Calvin cycle.
Conclusion
Calvin cycle is a series of chemical reactions that convert carbon dioxide and hydrogen carrier compounds into glucose.PGA and PGAL are two compounds taking part in the Calvin cycle. The main difference between PGA and PGAL is that PGA is an intermediate molecule of the Calvin cycle, whereas PGAL is the end product of the Calvin cycle.
Reference:
1. “Calvin Cycle.” Biology Dictionary.
2. “Calvin cycle.” Life of Plant.
Image Courtesy:
1. “Calvin cycle step 1” By Peter coxhead – Own work (CC0) via Commons Wikimedia
2. “Calvin-cycle4-sl” By Mike Jones – Own work (CC BY-SA 3.0) via Commons Wikimedia
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