acetyl CoA

(noun)

Acetyl coenzyme A or acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main function is to convey the carbon atoms within the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for energy production.

Related Terms

Examples of acetyl CoA in the following topics:

  • The Acetyl-CoA Pathway

    • The acetyl-CoA pathway utilizes carbon dioxide as a carbon source and often times, hydrogen as an electron donor to produce acetyl-CoA.
    • The following is a brief overview of the acetyl-CoA pathway. .
    • Acetyl-CoA synthetase is a class of enzymes that is key to the acetyl-CoA pathway.
    • The acetyl-CoA synthetase functions in combining the carbon monoxide and a methyl group to produce acetyl-CoA. .
    • Describe the role of the carbon monoxide dehydrogenase and acetyl-CoA synthetase in the acetyl-CoA pathway

  • The 3-Hydroxypropionate Cycle

    • The 3-hydroxypropionate cycle is a carbon fixation pathway that results in the production of acetyl-CoA and glyoxylate.
    • Specifically, in this cycle, the carbon dioxide is fixed by acetyl-CoA and propionyl-CoA carboxylases.
    • This process results in the formation of malyl-CoA which is further split into acetyl-CoA and glyoxylate.
    • The acetyl-CoA carboxylase utilized in this cycle is biotin-dependent as well and catalyzes the carboxylation of acetyl-CoA to malonyl-CoA.
    • This pathway produces pyruvate via conversion of bicarbonate and also results in the production of intermediates such as acetyl-CoA, gloxylate and succinyl-CoA.

  • Acetyl CoA and the Citric Acid Cycle

    • Through the catabolism of sugars, fats, and proteins, a two carbon organic product acetate in the form of acetyl-CoA is produced.
    • Acetyl-CoA along with two equivalents of water (H2O) are consumed by the citric acid cycle, producing two equivalents of carbon dioxide (CO2) and one equivalent of HS-CoA.
    • This generates acetyl-CoA according to the following reaction scheme:
    • CH3C(=O)C(=O)O– (pyruvate) + HSCoA + NAD+ → CH3C(=O)SCoA (acetyl-CoA) + NADH + H+ + CO2
    • The product of this reaction, acetyl-CoA, is the starting point for the citric acid cycle.

  • Organic Acid Metabolism

    • This process requires the β-oxidation pathway, a cyclic process that catalyzes the sequential shortening of fatty acid acyl chains to the final product, acetyl-CoA.
    • Fatty acid chains are converted to enoyl-CoA (catalyzed by acyl-CoA dehydrogenase).
    • 3-ketoacyl-CoA is thiolated (by 3-ketoacyl-CoA thiolase) to yield one molecule of acetyl-CoA and a derivative of the original input fatty acid that is now shorter by two carbons.
    • Acertyl-CoA is the entry molecule for the TCA cycle.
    • Free fatty acids are broken down to acetyl-CoA by dedicated enzymes in the β-oxidation pathway.

  • Biosynthesis and Energy

    • Biosynthesis in living organisms is a process in which substrates are converted to more complex products.
    • There are numerous mechanisms in place to ensure biosynthetic pathways are properly controlled so a cell will produce a specific amount of a compound.
    • A majority of these processes are considered to be multi-step or multi-enzymatic processes.
    • The major pathways utilized to ensure fixation of carbon dioxide include: the Calvin cycle, the reductive TCA cycle, and the acetyl-CoA pathway.
    • In the acetyl-CoA pathway, carbon dioxide is reduced to carbon monoxide and then acetyl-CoA.

  • The Reverse TCA Cycle

    • Reverse TCA, a form of carbon fixation, utilizes numerous ATP molecules, hydrogen and carbon dioxide to generate an acetyl CoA.
    • ATP citrate lyase is the enzyme responsible for cleaving citrate into oxaloacetate and acetyl CoA.
    • 4) succinate is converted to succinyl-CoA (ATP is hydrolyzed to ADP+Pi)
    • 5) succincyl CoA is converted to alpha-ketoglutarate via an alpha-ketoglutarate synthase (reduction of carbon dioxide occurs and oxidation of coenzyme A)
    • 8) ATP citrate lyase is then used to convert citrate to oxaloacetate and acetyl CoA (ATP is hydrolyzed to ADP and Pi).

  • Lipid Metabolism

    • These fatty acids can then enter a dedicated pathway that promotes step-wise lipid processing that ultimately yields acetyl-CoA, a critical metabolite that conveys carbon atoms to the TCA cycle (aka Krebs cycle or citric acid cycle) to be oxidized for energy production.
    • The acetyl-CoA molecule liberated by this process is eventually converted into ATP through the TCA cycle.
    • Oxidation: The initial step of β-oxidation is catalyzed by acyl-CoA dehydrogenase, which oxidizes the fatty acyl-CoA molecule to yield enoyl-CoA.
    • Cleavage: A thiolase then cleaves off acetyl-CoA from the oxidized molecule, which also yields an acyl-CoA that is two carbons shorter than the original molecule that entered the β-oxidation pathway.
    • This cycle repeats until the fatty acid has been completely reduced to acetyl-CoA, which is fed through the TCA cycle to ultimately yield cellular energy in the form of ATP .

  • Types of Catabolism

    • Next, these smaller molecules are taken up by cells and converted to yet smaller molecules, usually the acetyl coenzyme A (acetyl-CoA), which releases some energy.
    • Finally, the acetyl group on the CoA is oxidized to water and carbon dioxide in the citric acid cycle and electron transport chain, releasing the energy that is stored by reducing the coenzyme nicotinamide adenine dinucleotide (NAD+) into NADH.
    • Pyruvate is an intermediate in several metabolic pathways, but the majority is converted to acetyl-CoA and fed into the citric acid cycle.
    • Although some more ATP is generated in the citric acid cycle, the most important product is NADH, which is made from NAD+ as the acetyl-CoA is oxidized.
    • The glycerol initiates glycolysis and the fatty acids are broken down by beta oxidation to release acetyl-CoA, which then is fed into the citric acid cycle.

  • Pyruvic Acid and Metabolism

    • Pyruvic acid can be made from glucose through glycolysis, converted back to carbohydrates (such as glucose) via gluconeogenesis, or to fatty acids through acetyl-CoA.
    • Pyruvate is converted into acetyl-coenzyme A, which is the main input for a series of reactions known as the Krebs cycle.
    • Pyruvate is a key intersection in the network of metabolic pathways.
    • Pyruvate can be converted into carbohydrates via gluconeogenesis, to fatty acids or energy through acetyl-CoA, to the amino acid alanine, and to ethanol.
    • Pyruvic acid can be made from glucose through glycolysis, converted back to carbohydrates (such as glucose) via gluconeogenesis, or to fatty acids through acetyl-CoA.

  • Lipid Biosynthesis

    • This involves the synthesis of fatty acids from acetyl-CoA and the esterification of fatty acids in the production of triglycerides, a process called lipogenesis.
    • Fatty acids are made by fatty acid synthases that polymerize and then reduce acetyl-CoA units.
    • For example, in humans, the desaturation of stearic acid by stearoyl-CoA desaturase-1 produces oleic acid.
    • Triglyceride synthesis takes place in the endoplasmic reticulum by metabolic pathways in which acyl groups in fatty acyl-CoAs are transferred to the hydroxyl groups of glycerol-3-phosphate and diacylglycerol.
    • In archaea, the mevalonate pathway produces these compounds from acetyl-CoA, while in plants and bacteria the non-mevalonate pathway uses pyruvate and glyceraldehyde 3-phosphate as substrates.