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by Anonymous on October 27th, 2009

Anonymous

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In c3 and c4 photosynthesis, how are the actions of RuBP carboxylase and PEP case contrasting?

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  • by singularitygirl on October 30th, 2009

    singularitygirl

    Your question is carbon fixation.

    RuBp is part of the Calvin cycle where carbon fixation produces a product which is then converted to the final carbohydrate products. In the fixation or reduction of CO2, CO2 combines with RuBP, your five carbon sugar to yield two molecules of a three carbon compound 3-phosphoglycerate (PGA) that in the presence of ATP and NADPH from the light-dependent stages, is reduced to glyceraldehyde 3-phosphate (G3P). This product is also referred to as 3-phosphoglyceraldehyde (PGAL).

    In short, in C3 plants the primary carboxylation reaction, catalyzed by rubisco, produces the three-carbon sugar 3-phosphoglyceric acids directly in the Calvin cycle, (lacking PEP-carboxylase thats for c4)


    C4 refers to a group of plants with a special adaptation to dry conditons where the stomata will close to prevent water loss and as a consequence CO2 and O2 will also decrease. The C4 adaptation can overcome these losses and also produce more sugars.

    Carbon dioxide is fixed in the cells of the mesophyll by adding it to the three-carbon molecule phosphoenolpyruvate (PEP), a reaction catalyzed by an enzyme called PEP carboxylase and which creates the four-carbon organic acid, oxaloacetic acid. Oxaloacetic acid or malate synthesized and translocated to cells where the enzyme, rubisco and calvin cyle enzymes are located. CO2 will be released by decarboxylation of the four-carbon acids and fixed by rubisco to the three-carbon sugar 3-Phosphoglyceric acids. The physical separation of rubisco from the oxygen-generating light reactions reduces photorespiration and increases CO2 fixation and thus photosynthetic capacity of the leaf.

    enjoy! Sorry If I wasnt detailed, its my bed time!

    Night!

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