keto acid
(noun)
Any carboxylic acid that also contains a ketone group.
Examples of keto acid in the following topics:
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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 supplies energy to living cells through the citric acid cycle (also known as the Krebs cycle) when oxygen is present (aerobic respiration); when oxygen is lacking, it ferments to produce lactic acid.
- The cycle is also known as the citric acid cycle or tri-carboxylic acid cycle, because citric acid is one of the intermediate compounds formed during the reactions.
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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.
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Absorptive State
- This main product of fat digestion is first broken down to fatty acids and glycerol through hydrolysis using lipoprotein lipase.
- The liver deaminates amino acids to keto acids to be used in the Kreb's cycle in order to generate energy in the form of ATP.
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Types of Catabolism
- Fats are catabolised by hydrolysis to free fatty acids and glycerol.
- 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.
- The amino group is fed into the urea cycle, leaving a deaminated carbon skeleton in the form of a keto acid.
- Several of these keto acids are intermediates in the citric acid cycle, for example the deamination of glutamate forms α-ketoglutarate.
- The glucogenic amino acids can also be converted into glucose, through gluconeogenesis.
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Reductions & Oxidations of Carboxylic Acids
- Sodium borohydride, NaBH4, does not reduce carboxylic acids; however, hydrogen gas is liberated and salts of the acid are formed.
- Partial reduction of carboxylic acids directly to aldehydes is not possible, but such conversions have been achieved in two steps by way of certain carboxyl derivatives.
- Lead tetraacetate will also oxidize mono-carboxylic acids in a manner similar to reaction #1.
- Finally, the third example illustrates the general decarboxylation of β-keto acids, which leaves the organic residue in a reduced state (note that the CO2 carbon has increased its oxidation state. ).
- Also, various iodide derivatives may be prepared directly from the corresponding carboxylic acids.
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Amino Acid Synthesis
- These polymers are linear and unbranched, with each amino acid within the chain attached to two neighboring amino acids.
- Twenty-two amino acids are naturally incorporated into polypeptides and are called proteinogenic or natural amino acids.
- All amino acids are synthesized from intermediates in glycolysis, the citric acid cycle, or the pentose phosphate pathway.
- Amino acid synthesis depends on the formation of the appropriate alpha-keto acid, which is then transaminated to form an amino acid.
- Examples include lanthionine, 2-aminoisobutyric acid, dehydroalanine, and the neurotransmitter gamma-aminobutyric acid.
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Mechanism of Electrophilic α-Substitution
- (iv) Enolization is catalyzed by acids and bases.
- A full description of the acid and base-catalyzed keto-enol tautomerization process (shown below) discloses that only two intermediate species satisfy this requirement.
- These are the enol tautomer itself and its conjugate base (common with that of the keto tautomer), usually referred to as an enolate anion.
- Together with some related acidities, this is listed in the following table.
- Even though enol tautomers are about a million times more acidic than their keto isomers, their low concentration makes this feature relatively unimportant for many simple aldehydes and ketones.
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Aldehydes and Ketones
- Ketones have alpha-hydrogens which participate in keto-enol tautomerism.
- The keto form predominates at equilibrium for most ketones.
- The interconversion can be catalyzed by the presence of either an acid or a base.
- In the presence of strong oxidizing agents, they can be oxidized to carboxylic acids.
- The interconversion between the two forms can be catalyzed by an acid or a base.
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Hydration of Alkynes and Tautomerism
- As with alkenes, the addition of water to alkynes requires a strong acid, usually sulfuric acid, and is facilitated by mercuric sulfate.
- The explanation for this deviation lies in enol-keto tautomerization, illustrated by the following equation.
- Tautomeric equilibria are catalyzed by traces of acids or bases that are generally present in most chemical samples.
- Two factors have an important influence on the enol-keto tautomerizations described here.
- The keto tautomer has a 17.5 kcal/mole advantage in bond energy, so its predominance at equilibrium is expected.
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The Aldol Reaction
- Stepwise mechanisms for the base-catalyzed and acid-catalyzed reactions are seen in the third and fourth diagrams below.
- The dehydration step of an aldol condensation is also reversible in the presence of acid and base catalysts.
- The acid-catalyzed elimination of water is not exceptional, since this was noted as a common reaction of alcohols.
- As shown by the equations, these eliminations might proceed from either the keto or enol tautomers of the beta-hydroxy aldol product.
- Although the keto tautomer route is not unreasonable (recall the enhanced acidity of the alpha-hydrogens in carbonyl compounds), the enol tautomer provides a more favorable pathway for both acid and base-catalyzed elimination of the beta oxygen.