which stereoisomer of citric acid is produced in the citric acid cycle?
The citric acid cycle, also known as the Krebs cycle, is a central metabolic pathway that occurs in the mitochondria of cells. It is responsible for generating energy in the form of ATP and involves a series of chemical reactions. In the citric acid cycle, citric acid (or citrate) is initially formed.
To determine the stereoisomer of citric acid produced in the citric acid cycle, we need to consider the structure of citric acid. Citric acid has three carboxylic acid groups (COOH) and a hydroxyl group (OH). It exists as a tricarboxylic acid with the molecular formula C₆H₈O₇.
In the citric acid cycle, the stereoisomer of citric acid produced is the (S)-isomer, also known as (-)-isocitric acid. This isomer has the hydroxyl group on the same side as the carboxylic acid groups.
To determine this, one way is by analyzing the enzymatic reactions that occur in the citric acid cycle. The enzyme aconitase catalyzes the conversion of citrate to isocitrate. During this reaction, the hydroxyl group of citrate gets relocated to the other side of the molecule, resulting in the formation of isocitrate. This process is an example of stereoisomerism, as the orientation of the hydroxyl group changes.
Therefore, in the citric acid cycle, citrate is converted to the (S)-isomer, (-)-isocitrate, during the aconitase-catalyzed reaction.