C4 carbon fixation

Examples of C4 carbon fixation in the following topics:

• CAM and C4 Photosynthesis

  • In contrast to C4 metabolism, which physically separates the CO2 fixation to PEP from the Calvin cycle, CAM temporally separates these two processes.
  • Decarboxylation of malate during the day releases CO2 inside the leaves, thus allowing carbon fixation to 3-phosphoglycerate by RuBisCO.
  • Due to the inactivity required by the CAM mechanism, C4 carbon fixation has a greater efficiency in terms of PGA synthesis.
  • Plants that do not use PEP-carboxylase in carbon fixation are called C3 plants because the primary carboxylation reaction, catalyzed by RuBisCO, produces the three-carbon 3-phosphoglyceric acids directly in the Calvin-Benson cycle.
  • Over 90% of plants use C3 carbon fixation, compared to 3% that use C4 carbon fixation; however, the evolution of C4 in over 60 plant lineages makes it a striking example of convergent evolution.

• Study of Photosynthesis

  • Mass spectrometry has been used to study the ratio of carbon isotopes in various plants to understand the mechanisms of photosynthesis.
  • Stable carbon isotopes in carbon dioxide are utilized differentially by plants during photosynthesis.
  • C3 carbon fixation is a metabolic pathway that converts carbon dioxide and ribulose bisphosphate into 3-phosphoglycerate.
  • In C4 plants, carbon dioxide is drawn out of malate and into this reaction rather than being drawn directly from the air.
  • Grasses in hot, arid environments, specifically maize, but also millet, sorghum, sugar cane, and crabgrass, follow a C4 photosynthetic pathway that produces higher ratios of 13C to 12C.

• Carboxysomes

  • Carboxysomes are intracellular structures that contain enzymes involved in carbon fixation and found in many autotrophic bacteria.
  • They are proteinaceous structures resembling phage heads in their morphology; they contain the enzymes of carbon dioxide fixation in these organisms.
  • It is thought that the high local concentration of the enzymes, along with the fast conversion of bicarbonate to carbon dioxide by carbonic anhydrase, allows faster and more efficient carbon dioxide fixation than is possible inside the cytoplasm.
  • Carboxysomes are bacterial microcompartments that contain enzymes involved in carbon fixation.
  • These compartments are thought to concentrate carbon dioxide to overcome the inefficiency of RuBisCo (ribulose bisphosphate carboxylase/oxygenase) - the predominant enzyme in carbon fixation and the rate limiting enzyme in the Calvin cycle.

• Oxygenic Photosynthesis

  • Oxygenic photosynthesis, provides energy to organism and allows for carbon fixation, all the while producing oxygen as a byproduct.
  • Photosynthesis is not only needed by photosynthetic organism for energy but also for carbon fixation .
  • Carbon dioxide is converted into sugars in a process called carbon fixation.
  • Carbon fixation is a redox reaction, so photosynthesis needs to supply both a source of energy to drive this process, and the electrons needed to convert carbon dioxide into a carbohydrate, which is a reduction reaction.
  • In general outline, photosynthesis is the opposite of cellular respiration, where glucose and other compounds are oxidized to produce carbon dioxide, water, and release chemical energy.

• The 3-Hydroxypropionate Cycle

  • The 3-hydroxypropionate cycle is a carbon fixation pathway that results in the production of acetyl-CoA and glyoxylate.
  • Carbon fixation is a key pathway in numerous microorganisms, resulting in the formation of organic compounds deemed necessary for cellular processes.
  • One of the pathways that is utilized for carbon fixation is the 3-hydroxypropionate cycle.
  • Specifically, in this cycle, the carbon dioxide is fixed by acetyl-CoA and propionyl-CoA carboxylases.
  • However, the cycle can be broken down into two major phases, carbon dioxide fixation and glyoxylate assimilation.

• Biosynthesis and Energy

  • Carbon dioxide fixation is necessary to ensure carbon dioxide can be converted into organic carbon.
  • The major pathways utilized to ensure fixation of carbon dioxide include: the Calvin cycle, the reductive TCA cycle, and the acetyl-CoA pathway.
  • The Calvin cycle involves utilizing carbon dioxide and water to form organic compounds.
  • The reductive TCA cycle, commonly referred to as the reverse Krebs cycle, also produces carbon compounds from carbon dioxide and water.
  • In the acetyl-CoA pathway, carbon dioxide is reduced to carbon monoxide and then acetyl-CoA.

• Nitrogen Fixation: Root and Bacteria Interactions

  • The NH3 resulting from fixation can be transported into plant tissue and incorporated into amino acids, which are then made into plant proteins.
  • Soil bacteria, collectively called rhizobia, symbiotically interact with legume roots to form specialized structures called nodules in which nitrogen fixation takes place .
  • Through symbiotic nitrogen fixation, the plant benefits from using an endless source of nitrogen from the atmosphere.
  • As in any symbiosis, both organisms benefit from the interaction: the plant obtains ammonia and bacteria obtain carbon compounds generated through photosynthesis, as well as a protected niche in which to grow.
  • Abiotic nitrogen fixation has been omitted.

• Regulation of the Calvin Cycle

  • The Calvin cycle is a process that ensures carbon dioxide fixation in plants.
  • The Calvin cycle is a process utilized to ensure carbon dioxide fixation.
  • During the first phase of the Calvin cycle, carbon fixation occurs.
  • The regulation of the Calvin cycle requires many key enzymes to ensure proper carbon fixation.
  • Outline the three major phases of the Calvin cycle: carbon fixation, reduction, and regeneration of ribulose

• Intermediates Produced During the Calvin Cycle

  • The Calvin Cycle involves the process of carbon fixation to produce organic compounds necessary for metabolic processes.
  • The Calvin Cycle is characterized as a carbon fixation pathway.
  • The process of carbon fixation involves the reduction of carbon dioxide to organic compounds by living organisms.
  • The Calvin cycle is most often associated with carbon fixation in autotrophic organisms, such as plants, and is recognized as a dark reaction.
  • In organisms that require carbon fixation, the Calvin cycle is a means to obtain energy and necessary components for growth.

• Role of Microbes in Biogeochemical Cycling

  • The key collective metabolic processes of microbes (including nitrogen fixation, carbon fixation, methane metabolism, and sulfur metabolism) effectively control global biogeochemical cycling.
  • Carbon is critical for life because it is the essential building block of all organic compounds.
  • Carbon in the form of carbon dioxide (CO2) is readily obtained from the atmosphere, but before it can be incorporated into living organisms it must be transformed into a usable organic form.
  • The transformative process by which carbon dioxide is taken up from the atmospheric reservoir and "fixed" into organic substances is called carbon fixation.
  • Perhaps the best known example of carbon fixation is photosynthesis, a process by which energy derived from sunlight is harnessed to form organic compounds.