The process of carbon fixation has been an area of enhanced interest and researc
ID: 256751 • Letter: T
Question
The process of carbon fixation has been an area of enhanced interest and research in the last decade or so
A. Why is that? Elaborate
B. For C3 plants, provide the following: a summary equation for each of the three stages of the Calvin cycle and then one summary equation for the entire process of the cycle.
C. What is the inefficiency that is inherent in the first stage of rthe Calvin cycle, due to an issue associated with the enzyme rubisco? Explain
D. C4 and CAM plants do not have the inefficnecy. Why not? How do they avoid the inefficiency? Explain?
Explanation / Answer
Answer:
A).At first, people thought that carbon fixation only by c3 cycle. But later several types of carbon fixation has been identified by many researchers. Those are C4 & CAM cycle.
B).
Carbon fixation:
6CO2+ 6RUBP -----12 Phosphoglyceric acid (PGA)
Reduction:
12 PGA+ 12ATP + 12NADPH2 -----10 Phosphoglyceraldehyde + glucose +12 ADP + 12 ip + 12 NADP+
Regenaration:
10 phosphoglyceric acid + 6 ATP ------6 RUBP + 6ADP + 6 ip
Summary equation for the entire process of the C3 cycle:
6CO2 + 6RUBP + 18ATP + 12 NADPH2 -------------C6H12O6 + 6 RUBP + 18 ADP + 18 ip + 12 NADP+
C).
RUBISCO enzyme catalyzes the first step of C3 cycle. When CO2 concentration is high, then the enzyme catalyzes carboxylation. But if O2 concentration is high, then the enzyme catalyzes oxygenation reaction, which leads to a waste process called as photorespiration. The photorespiration reduces the capacity of carbon fixation.
D).
C4 and CAM plants use PEP carboxylase to catalyzes the carboxylation reaction instead of RUBISCO PEP carboxylase. The PEP carboxylase enzyme doesn't undergo any oxygenation reaction, thereby there will be no chance of photorespiration. Thus the C4 and CAM plants do not have the inefficiency.
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