Reverse Krebs cycle
Encyclopedia
The reverse Krebs cycle (also known as the reverse tricarboxylic acid cycle, the reverse TCA cycle, or the reverse citric acid cycle)
is a sequence of chemical reactions that are used by some bacteria to produce carbon compounds from carbon dioxide
and water.
The reaction is the citric acid cycle
run in reverse: Where the Krebs cycle takes complex carbon
molecules in the form of sugars and oxidizes them to CO2 and water, the reverse cycle takes CO2 and water to make carbon compounds.
This process is used by some bacteria
to synthesise carbon compounds, sometimes using hydrogen
, sulfide
, or thiosulfate
as electron donor
s. In this process, it can be seen as an alternative to the far more common photosynthesis
production of organic molecules.
The reaction is a possible candidate for prebiotic early-earth conditions and, so, is of interest in the research of the origin of life. It has been found that some of the steps can be catalysed by minerals.
is a sequence of chemical reactions that are used by some bacteria to produce carbon compounds from carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
and water.
The reaction is the citric acid cycle
Citric acid cycle
The citric acid cycle — also known as the tricarboxylic acid cycle , the Krebs cycle, or the Szent-Györgyi-Krebs cycle — is a series of chemical reactions which is used by all aerobic living organisms to generate energy through the oxidization of acetate derived from carbohydrates, fats and...
run in reverse: Where the Krebs cycle takes complex carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
molecules in the form of sugars and oxidizes them to CO2 and water, the reverse cycle takes CO2 and water to make carbon compounds.
This process is used by some bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
to synthesise carbon compounds, sometimes using hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
, or thiosulfate
Thiosulfate
Thiosulfate is an oxyanion of sulfur. The prefix thio indicates that thiosulfate ion is a sulfate ion with one oxygen replaced by a sulfur. Thiosulfate occurs naturally and is produced by certain biochemical processes...
as electron donor
Electron donor
An electron donor is a chemical entity that donates electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process....
s. In this process, it can be seen as an alternative to the far more common photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
production of organic molecules.
The reaction is a possible candidate for prebiotic early-earth conditions and, so, is of interest in the research of the origin of life. It has been found that some of the steps can be catalysed by minerals.