Question

Bioinformatics has identified some enzymes used in the citric acid cycle in primitive bacteria. Once such a cycle utilized many of the citric acid cycle intermediates but occurred in the reverse direction. Researchers suspect which of the following based on this information?

a. Researchers suspect that primitive prokaryotic use of the citric acid enzymes were focused on the production of CO2 rather than the use of CO2.
b. Researchers suspect that early methods for converting pyruvate to acetyl CoA did not exist.
c. Researchers suspect that the "original" citric acid cycle was used by all species.
d. Researchers suspect that the current "clockwise" version of the citric acid cycle could be used to help humans feed off CO2.
e. Researchers suspect that portions of the reverse cycle may have been responsible for fixing CO2

Answer 1

e. Researchers suspect that portions of the reverse cycle may have been responsible for fixing CO2

Step-by-step explanation:

Carbon fixation refers to the metabolic process by which inorganic carbon, especially carbon dioxide (CO2), is converted to organic matter. Moreover, the citric acid cycle (TCA) is a metabolic pathway capable of generating energy by the oxidation of acetate (which is derived from carbohydrates, fats, and proteins) into CO2. The reverse TCA cycle is a form of carbon fixation that ​uses CO2 and water molecules to produce organic carbon molecules. The enzymes that are unique to the reverse TCA cycle include ATP citrate lyase (required to cleave citrate into acetyl CoA and oxalacetate); 2-oxoglutarate:ferredoxin oxidoreductase (OGOR); and pyruvate ferredoxin oxidoreductase (required for pyruvate decarboxylation/oxidation).