Question

Which compound is four-carbon compounds in the C-3 cycle?
a) Erythrose-4-phosphate
b) Dihydroxyacetone phosphate
c)3-Phosphoglyceraldehyde
d)Oxalo acetic acid

Answer 1

HintThe C3 pathway or the Calvin cycle is the pathway in which the carbon dioxide fixation is done in the absence of the sunlight. Calvin cycle occurs in the plants. They take in carbon dioxide released by organisms and use it to make simple sugars. The Calvin cycle involves three steps which are fixation, reduction, and regeneration.

Complete answer: The compound Erythrose -4-phosphate is the four-carbon molecule which is formed in the Calvin cycle. It is a phosphate of the simple sugar erythrose molecule. It is an intermediate product in the Calvin cycle as well as in the pentose phosphate cycle.

Additional information: Calvin cycle occurs in three steps of fixation, reduction, and regeneration. To start the cycle energy resources are required. These energy resources are met by the ATP and NADPH present in the plant cell which is derived from the sun’s energy. Calvin cycle uses these energy molecules to convert the three molecules of carbon dioxide to one molecule of the three-carbon sugar. In the Calvin cycle, three molecules of carbon dioxide and water are converted into one molecule of glyceraldehyde, during this process six atoms of oxygen are formed which are released into the atmosphere for organisms to use for respiration. In the first stage of the cycle fixation of carbon dioxide occurs, as it is converting from an inorganic molecule to an organic molecule. This stage also witnesses the initiation of the light-independent reactions. In the second stage of the cycle which is a reduction, ATP and NADPH are used to reduce 3-PGA into G-3-P, and conversion of ATP and NADPH to ADP and NADP+ occurs. The last stage of the cycle is the regeneration stage where RuBP is regenerated so that more carbon dioxide can be fixed in the plants.

So, the answer is ‘Erythrose-4-phosphate’.

Note: Erythrose-4-phosphate is the compound which is present in both Calvin cycle as well as in the pentose phosphate cycle. It is useful as it is the precursor in the biosynthesis of the aromatic compounds.