Photorespiration Is a Wasteful Process

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Assignment 03

Photorespiration is a wasteful process.

Plant Biochemistry
Department of Life sciences
Name- Mahnaz Reza
ID- 072 398 047
Date- the 16th of March 2011, Wednesday

Photorespiration, as the name suggests is the process by which the most abaundant protein on earth, RubisCO, uses up oxygen or adds oxygen to the 5 carbon sugar rubisco bisphosphate, instead of carbon dioxide as in the process of photosynthesis. It is the alternate pathway used by the enzyme. This enzyme being both a carboxylase and an oxygenase does not have the capability to differentiate between the carbon dioxide molecule or the oxygen molecule as a result of which it can assist in both the reaction of photorespiration and photosynthesis, even though they are the opposite pathways. In general RubisCO favours carbon dioxide to oxygen, and approximately 3 carboxylations occur per oxygenation. It is interesting to note that photorespiration only occurs in C3 plants where the oxygenase plays its role. It is important because it is a major source of H2O2 in photosynthetic cells. Through H2O2 production and pyridine nucleotide interactions, photorespiration makes a key contribution to cellular redox homeostasis. In so doing, it influences multiple signaling pathways, particularly those that govern plant hormonal responses controlling growth, environmental and defense responses, and programmed cell death Photorespiration occurs when carbon dioxide levels within the leaf tissue dwindle to about 50 parts per million, usually on a hot, dry day where a plant has closed its stomates to prevent water loss. At this concentration of CO2, oxygen reacts with ribulose bisphosphate (RuBP) in the presence of RubisCO, and creates 2 molecules of 3-phosphoglycerate and 1 molecule of 2-phosphoglycolate. Under normal oxygen and carbon dioxide concentrations, the reaction is between CO2, RuBP, and RubisCO to produce 12 molecules of 3-phosphoglycerate. 2-phosphoglycolate is toxic, so the plant has...
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