pyruvic acid

(noun)

A colourless liquid; an important intermediate in the metabolism of proteins and carbohydrates, and in fermentation.

Related Terms

Examples of pyruvic acid in the following topics:

  • Pyruvic Acid and Metabolism

    • Pyruvic acid (CH3COCOOH) is an organic acid, a ketone, and the simplest of the alpha-keto acids.
    • Pyruvic acid (CH3COCOOH; is an organic acid, a ketone, and the simplest of the alpha-keto acids.
    • The carboxylate (COO−) anion of pyruvic acid.
    • 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 can be converted into carbohydrates via gluconeogenesis, to fatty acids or energy through acetyl-CoA, to the amino acid alanine, and to ethanol.

  • Fermentation Without Substrate-Level Phosphorylation

    • During fermentation, pyruvate is metabolised to various compounds.
    • Homolactic fermentation is the production of lactic acid from pyruvate; alcoholic fermentation is the conversion of pyruvate into ethanol and carbon dioxide; and heterolactic fermentation is the production of lactic acid as well as other acids and alcohols.
    • 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.
    • It can also be used to construct the amino acid alanine and be converted into ethanol.
    • Pyruvic acid supplies energy to living cells through the citric acid cycle (also known as the Krebs cycle) when oxygen is present (aerobic respiration), and alternatively ferments to produce lactic acid when oxygen is lacking (fermentation).

  • Anaerobic Cellular Respiration

    • The chemical reactions of lactic acid fermentation are the following:
    • Once the lactic acid has been removed from the muscle and circulated to the liver, it can be reconverted into pyruvic acid and further catabolized for energy.
    • Pyruvic acid → CO2 + acetaldehyde + NADH → ethanol + NAD+
    • A carboxyl group is removed from pyruvic acid, releasing carbon dioxide as a gas.
    • The fermentation of pyruvic acid by yeast produces the ethanol found in alcoholic beverages.

  • Outcomes of Glycolysis

    • Glycolysis starts with one molecule of glucose and ends with two pyruvate (pyruvic acid) molecules, a total of four ATP molecules, and two molecules of NADH .
    • If the cell cannot catabolize the pyruvate molecules further (via the citric acid cycle or Krebs cycle), it will harvest only two ATP molecules from one molecule of glucose.
    • Additionally, the last step in glycolysis will not occur if pyruvate kinase, the enzyme that catalyzes the formation of pyruvate, is not available in sufficient quantities.
    • Thus, pyruvate kinase is a rate-limiting enzyme for glycolysis.
    • Glycolysis, or the aerobic catabolic breakdown of glucose, produces energy in the form of ATP, NADH, and pyruvate, which itself enters the citric acid cycle to produce more energy.

  • Breakdown of Pyruvate

    • After glycolysis, pyruvate is converted into acetyl CoA in order to enter the citric acid cycle.
    • Acetyl CoA is a molecule that is further converted to oxaloacetate, which enters the citric acid cycle (Krebs cycle).
    • The conversion of pyruvate to acetyl CoA is a three-step process .
    • This molecule of acetyl CoA is then further converted to be used in the next pathway of metabolism, the citric acid cycle.
    • Each pyruvate molecule loses a carboxylic group in the form of carbon dioxide.

  • Muscle Fatigue

    • With insufficient oxygen, pyruvate cannot enter the Krebs cycle and instead accumulates in the muscle fiber.
    • Pyruvate is continually processed into lactic acid.
    • With pyruvate accumulation, lactic acid production is also increased.
    • This lactic acid accumulation in the muscle tissue reduces the pH, making it more acidic and producing the stinging feeling in muscles when exercising.
    • Lactic acid can be converted back to pyruvate in well-oxygenated muscle cells; however, during exercise the focus in on maintaining muscle activity.

  • Muscle Metabolism

    • Pyruvate is continually processed into lactic acid.
    • With pyruvate accumulation, the amount of lactic acid produced is also increased.
    • This lactic acid accumulation in the muscle tissue reduces the pH, making it more acidic and producing the stinging feeling in muscles when exercising.
    • While the pyruvate generated through glycolysis can accumulate to form lactic acid, it can also be used to generate further molecules of ATP.
    • Cellular respiration is limited by oxygen availability, so lactic acid can still build up if pyruvate in the Krebs Cycle is insufficient.

  • Connecting Proteins to Glucose Metabolism

    • However, if there are excess amino acids, or if the body is in a state of starvation, some amino acids will be shunted into the pathways of glucose catabolism.
    • The remaining atoms of the amino acid result in a keto acid: a carbon chain with one ketone and one carboxylic acid group.
    • The keto acid can then enter the citric acid cycle.
    • When deaminated, amino acids can enter the pathways of glucose metabolism as pyruvate, acetyl CoA, or several components of the citric acid cycle.
    • The carbon skeletons of certain amino acids (indicated in boxes) are derived from proteins and can feed into pyruvate, acetyl CoA, and the citric acid cycle.

  • Control of Catabolic Pathways

    • Fermentation, with its production of organic acids like lactic acid, frequently accounts for the increased acidity in a cell; however, the products of fermentation do not typically accumulate in cells.
    • The last step in glycolysis is catalyzed by pyruvate kinase.
    • The pyruvate produced can proceed to be catabolized or converted into the amino acid alanine.
    • Pyruvate kinase is also regulated by ATP (a negative allosteric effect).
    • If more energy is needed, more pyruvate will be converted into acetyl CoA through the action of pyruvate dehydrogenase.

  • Acetyl CoA and the Citric Acid Cycle

    • The citric acid cycle is a key component of the metabolic pathway by which all aerobic organisms generate energy.
    • The name of this metabolic pathway is derived from citric acid, a type of tricarboxylic acid that is first consumed and then regenerated by this sequence of reactions to complete the cycle.
    • One of the primary sources of acetyl-CoA is sugars that are broken down by glycolysis to produce pyruvate that, in turn, is decarboxylated by the enzyme pyruvate dehydrogenase.
    • 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.