Question
Diagrammatically explain the process of photorespiration.
✓
Answer
Mechanism:
$1.$ Photorespiration involves three organelles chloroplast, peroxisomes and mitochondria and occurs in a series of cyclic reactions which is also called $\text{PCO}$ cycle. $($Photosynthetic Carbon Cycle$)$
$2.$ Enzyme Rubisco acts as oxygenase at higher concentration of $O_2$ and photorespiration begins.
$3.$ When $RuBP$ reacts with $O_2$ rather than $CO_2$ to form a $3-$carbon compound $\text{(PGA)}$ and $2-$carbon compound phosphoglycolate.
$4.$ Phosphoglycolate is then converted to glycolate which is shuttled out of the chloroplast into the peroxisomes.
$5.$ In Peroxisomes, glycolate is converted into glyoxylate by enzyme glycolate oxidase.
$6.$ Glyoxylate is further converted into amino acid glycine by transamination.
$7.$ In mitochondria, two molecules of glycine are converted into serine $($amino acid$)$ and $CO_2$ is given out.
$8.$ Thus, it loses $25\%$ of photosynthetically fixed carbon.
$9.$Serine is transported back to peroxisomes and converted into glycerate.
$10.$ It is shuttled back to chloroplast to undergo phosphorylation and utilized in formation of $3-\text{PGA,}$ which get utilized in $C_3$ pathway.
$1.$ Photorespiration involves three organelles chloroplast, peroxisomes and mitochondria and occurs in a series of cyclic reactions which is also called $\text{PCO}$ cycle. $($Photosynthetic Carbon Cycle$)$
$2.$ Enzyme Rubisco acts as oxygenase at higher concentration of $O_2$ and photorespiration begins.
$3.$ When $RuBP$ reacts with $O_2$ rather than $CO_2$ to form a $3-$carbon compound $\text{(PGA)}$ and $2-$carbon compound phosphoglycolate.
$4.$ Phosphoglycolate is then converted to glycolate which is shuttled out of the chloroplast into the peroxisomes.
$5.$ In Peroxisomes, glycolate is converted into glyoxylate by enzyme glycolate oxidase.
$6.$ Glyoxylate is further converted into amino acid glycine by transamination.
$7.$ In mitochondria, two molecules of glycine are converted into serine $($amino acid$)$ and $CO_2$ is given out.
$8.$ Thus, it loses $25\%$ of photosynthetically fixed carbon.
$9.$Serine is transported back to peroxisomes and converted into glycerate.
$10.$ It is shuttled back to chloroplast to undergo phosphorylation and utilized in formation of $3-\text{PGA,}$ which get utilized in $C_3$ pathway.
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