C4 Plants
C4 carbon fixation is one of three biochemical processes, along with C3 and CAM photosynthesis, used to fix carbon. It is named for the 4-carbon molecule present in the first product of carbon fixation in the small subset of plants that use that process, in contrast to the 3-carbon molecule products in C3 plants.
C4 fixation is an elaboration of the more common C3 carbon fixation and is believed to have evolved more recently. C4 and CAM overcome the tendency of the enzyme RuBisCO to wastefully fix oxygen rather than carbon dioxide in the process of photorespiration. This is achieved in a more efficient environment for RubisCo by shuttling CO2 via malate or aspartate from mesophyll cells to bundle-sheath cells. In these bundle-sheath cells, RuBisCO is isolated from atmospheric oxygen and saturated with the CO2 released by decarboxylation of the malate. C4 plants use PEP Carboxylase to capture more CO2 in the mesophyl cells. PEP Carboxylase (3 carbons) binds to CO2 to make OAA. Then OAA makes malate (4 carbons). Then malate enters bundle sheath and release CO2 inside bundle sheath for rubisco to work more efficiently. These additional steps, however, require more energy in the form of ATP. Because of this extra energy requirement, C4 plants are able to more efficiently fix carbon in only certain conditions, with the more common C3 pathway being more efficient in other conditions.
C4 carbon fixation is one of three biochemical processes, along with C3 and CAM photosynthesis, used to fix carbon. It is named for the 4-carbon molecule present in the first product of carbon fixation in the small subset of plants that use that process, in contrast to the 3-carbon molecule products in C3 plants.
C4 fixation is an elaboration of the more common C3 carbon fixation and is believed to have evolved more recently. C4 and CAM overcome the tendency of the enzyme RuBisCO to
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