Question

What is photo-respiration and what is the process of it?

Answer 1

it is a process related to metabolism in plants which minimizes the effect of wasteful oxygenation by enzyme Rubisco.

There are some costs associated with this metabolic pathway one being the production of hydrogen peroxide in the peroxisome (associated with the conversion of glycolate to glyoxylate). Hydrogen peroxide is a dangerously strong oxidant which must be immediately broken down into water and oxygen by the enzyme catalase.

Addition of molecular oxygen to ribulose-1,5-bisphosphate produces 3-phosphoglycerate (PGA) and 2-phosphoglycolate (2PG, or PG). PGA is the normal product of carboxylation, and productively enters the Calvin cycle. Phosphoglycolate, however is also relatively difficult to recycle: in higher plants it is salvaged by a series of reactions in the peroxisome, mitochondria, and again in theperoxisome where it is converted into glycerate.

The conversion of 2x 2Carbon glycine to 1 C3 serine in the mitochondria by the enzyme glycine-decarboxylase is a key step, which releases CO₂, NH₃, and reduces NAD to NADH. Thus, 1 CO
2 molecule is produced for every 3 molecules of O
2 (two deriving from the activity of RuBisCO, the third from peroxisomal oxidations). The assimilation of NH₃ occurs via the GS-GOGAT cycle, at a cost of one ATP and one NADPH.