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Study the pathway given below:
In which of the following options are correct words for all the three blanks A, B and C indicated?
In which of the following options are correct words for all the three blanks A, B and C indicated?
A
A – Decarboxylation, B – Reduction, C – Regeneration
B
A – Fixation, B – Transamination, C – Regeneration
C
A – Fixation, B – Decarboxylation, C – Regeneration
D
A – Carboxylation, B – Decarboxylation, C – Reduction
Detailed Solution
The figure is the Hatch and Slack ($C_4$) pathway, showing a mesophyll cell and a bundle sheath cell.
A (in the mesophyll cell): atmospheric $CO_2$, as $HCO_3^-$, combines with the 3-carbon acceptor phosphoenol pyruvate (PEP) in the presence of PEP carboxylase to form the $C_4$ acid oxaloacetic acid. This is fixation.
The $C_4$ acid (malic or aspartic acid) is transported to the bundle sheath cell.
B (in the bundle sheath cell): the $C_4$ acid is broken down to release $CO_2$ and a 3-carbon acid. This is decarboxylation; the $CO_2$ released enters the Calvin cycle.
C (back in the mesophyll cell): the $C_3$ acid is transported back and converted into PEP again. This is regeneration of the primary acceptor.
Hence A – fixation, B – decarboxylation, C – regeneration.
A (in the mesophyll cell): atmospheric $CO_2$, as $HCO_3^-$, combines with the 3-carbon acceptor phosphoenol pyruvate (PEP) in the presence of PEP carboxylase to form the $C_4$ acid oxaloacetic acid. This is fixation.
The $C_4$ acid (malic or aspartic acid) is transported to the bundle sheath cell.
B (in the bundle sheath cell): the $C_4$ acid is broken down to release $CO_2$ and a 3-carbon acid. This is decarboxylation; the $CO_2$ released enters the Calvin cycle.
C (back in the mesophyll cell): the $C_3$ acid is transported back and converted into PEP again. This is regeneration of the primary acceptor.
Hence A – fixation, B – decarboxylation, C – regeneration.