Photorespiration in the context of "Biogeochemical cycle"

ā­ In the context of biogeochemical cycles, photorespiration is considered a process that contributes to the cycling of which element?

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ā­ Core Definition: Photorespiration

Photorespiration (also known as the oxidative photosynthetic carbon cycle or C2 cycle) refers to a process in plant metabolism where the enzyme RuBisCO oxygenates RuBP, wasting some of the energy produced by photosynthesis. The desired reaction is the addition of carbon dioxide to RuBP (carboxylation), a key step in the Calvinā€“Benson cycle, but approximately 25% of reactions by RuBisCO instead add oxygen to RuBP (oxygenation), creating a product that cannot be used within the Calvinā€“Benson cycle. This process lowers the efficiency of photosynthesis, potentially lowering photosynthetic output by 25% in C3 plants. Photorespiration involves a complex network of enzyme reactions that exchange metabolites between chloroplasts, leaf peroxisomes and mitochondria.

The oxygenation reaction of RuBisCO is a wasteful process because 3-phosphoglycerate is created at a lower rate and higher metabolic cost compared with RuBP carboxylase activity. While photorespiratory carbon cycling results in the formation of G3P eventually, around 25% of carbon fixed by photorespiration is re-released as CO2 and nitrogen, as ammonia. Ammonia must then be detoxified at a substantial cost to the cell. Photorespiration also incurs a direct cost of one ATP and one NAD(P)H.

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šŸ‘‰ Photorespiration in the context of Biogeochemical cycle

A biogeochemical cycle, or more generally a cycle of matter, is the movement and transformation of chemical elements and compounds between living organisms, the atmosphere, and the Earth's crust. Major biogeochemical cycles include the carbon cycle, the nitrogen cycle and the water cycle. In each cycle, the chemical element or molecule is transformed and cycled by living organisms and through various geological forms and reservoirs, including the atmosphere, the soil and the oceans. It can be thought of as the pathway by which a chemical substance cycles (is turned over or moves through) the biotic compartment and the abiotic compartments of Earth. The biotic compartment is the biosphere and the abiotic compartments are the atmosphere, lithosphere and hydrosphere.

For example, in the carbon cycle, atmospheric carbon dioxide is absorbed by plants through photosynthesis, which converts it into organic compounds that are used by organisms for energy and growth. Carbon is then released back into the atmosphere through respiration and decomposition. Additionally, carbon is stored in fossil fuels and is released into the atmosphere through human activities such as burning fossil fuels. In the nitrogen cycle, atmospheric nitrogen gas is converted by plants into usable forms such as ammonia and nitrates through the process of nitrogen fixation. These compounds can be used by other organisms, and nitrogen is returned to the atmosphere through denitrification and other processes. In the water cycle, the universal solvent water evaporates from land and oceans to form clouds in the atmosphere, and then precipitates back to different parts of the planet. Precipitation can seep into the ground and become part of groundwater systems used by plants and other organisms, or can runoff the surface to form lakes and rivers. Subterranean water can then seep into the ocean along with river discharges, rich with dissolved and particulate organic matter and other nutrients.

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Photorespiration in the context of Peroxisome

A peroxisome (/pəĖˆrɒksÉŖĖŒsoŹŠm/) is a membrane-bound organelle, a type of microbody, found in the cytoplasm of virtually all eukaryotic cells. Peroxisomes are oxidative organelles. Frequently, molecular oxygen serves as a co-substrate, from which hydrogen peroxide (H2O2) is then formed. Peroxisomes owe their name to hydrogen peroxide-generating and scavenging activities. They perform key roles in lipid metabolism and the reduction of reactive oxygen species.

Peroxisomes are involved in the catabolism of very long chain fatty acids, branched chain fatty acids, bile acid intermediates (in the liver), D-amino acids, and polyamines. Peroxisomes also play a role in the biosynthesis of plasmalogens: ether phospholipids critical for the normal function of mammalian brains and lungs. Peroxisomes contain approximately 10% of the total activity of two enzymes (Glucose-6-phosphate dehydrogenase and 6-Phosphogluconate dehydrogenase) in the pentose phosphate pathway, which is important for energy metabolism. It is debated whether peroxisomes are involved in isoprenoid and cholesterol synthesis in animals. Other peroxisomal functions include the glyoxylate cycle in germinating seeds ("glyoxysomes"), photorespiration in leaves, glycolysis in trypanosomes ("glycosomes"), and methanol and amine oxidation and assimilation in some yeasts.

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Photorespiration in the context of C4 photosynthesis

C4 carbon fixation or the Hatchā€“Slack pathway is one of three known photosynthetic processes of carbon fixation in plants. It owes the names to the 1960s discovery by Marshall Davidson Hatch and Charles Roger Slack.

C4 fixation is an addition to the ancestral and more common C3 carbon fixation. The main carboxylating enzyme in C3 photosynthesis is called RuBisCO, which catalyses two distinct reactions using either CO2 (carboxylation) or oxygen (oxygenation) as a substrate. RuBisCO oxygenation gives rise to phosphoglycolate, which is toxic and requires the expenditure of energy to recycle through photorespiration. C4 photosynthesis reduces photorespiration by concentrating CO2 around RuBisCO.

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Photorespiration in the context of Glutamine synthetase

Glutamine synthetase (GS) (EC 6.3.1.2) is an enzyme that catalyzes the condensation of glutamate and ammonia to form glutamine:Glutamate + ATP + NH3 ā†’ Glutamine + ADP + phosphate

Glutamine synthetase uses ammonia produced by nitrate reduction, amino acid degradation, and photorespiration. The amide group of glutamate is a nitrogen source for the synthesis of glutamine pathway metabolites.

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LINKED FROM (PARENTS)
← Biogeochemical cycle ← Peroxisome ← C4 photosynthesis ← Glutamine synthetase ← Biogeochemical cycling ← C4 carbon fixation ← Biogeochemical cycles
LINKS TO (CHILDREN)
Plant physiology → Enzyme → RuBisCO → RuBP → Carbon dioxide → Carboxylation → Calvinā€“Benson cycle → Oxygen → Oxygenase → C3 carbon fixation → Chloroplast → Peroxisome → Mitochondria → 3-Phosphoglyceric acid → Calvin cycle → Glyceraldehyde 3-phosphate → Ammonia → Adenosine triphosphate → NAD(P)H →