Question

Autotrophs don’t have to use just the Calvin cycle. Two other reactions that can fix carbon dioxide into organic molecules are the reverse citric acid cycle and the hydroxypropionate pathway. Research one of those and tell me how it works.

Answer 1

Calvin cycle is the predominant carbon fixing pathway in all autotrophs.

However certain times carbon fixation takes place through other pathways like reverse citric acid cycle and hydroxypropionate pathway.

In both the methods carbon dioxide and water are backed to form a carbon compound called Acetyl Co A.

Citric acid cycle proceeds by enzymatically degrading Acetyl Co A to carbon dioxide and water.

In reverse citric acid cycle carbon dioxide and water are used to form Acetyl Co A.

Beginning with oxalosuccinate, malate, fumarate, succinate, succinyl co A, 2-oxoglutarate, iso citrate, citrate and finally forms Acetyl Co A. This is just the reversal of Citric Acid Cycle.

In hydroxypropionate pathway carbon dioxide combines with hydrogen to form Acetyl Co A which is a carbon compound.