Metabolism of Nitrogenous Compounds

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Questions and Answers

Which of the following is a direct precursor for the synthesis of nonessential amino acids?

  • Intermediates of metabolism only
  • Both essential amino acids and metabolic intermediates (correct)
  • Fatty acids and glycerol
  • Essential amino acids only

What process describes incorporating nitrogen during biosynthesis, relative to the separation of amino groups?

  • The oxidation process
  • An unrelated metabolic pathway
  • A parallel catabolic process
  • A reversed chemical reaction (correct)

What are the two main stages in the degradation of amino acids?

  • Decarboxylation and reamination
  • Separation of the amino group and the metabolism of the carbon skeleton (correct)
  • Glycolysis and gluconeogenesis
  • Transamination and lipolysis

From what amino acid is dopamine synthesized?

<p>Tyrosine (B)</p> Signup and view all the answers

Which biogenic amine is associated with inflammatory reactions, gastric acid secretion, and neural transduction?

<p>Histamine (D)</p> Signup and view all the answers

Porphyria is a disorder related to problems in the synthesis of which of the following?

<p>Porphyrins (A)</p> Signup and view all the answers

What are the key sources for nitrogen used in purine synthesis?

<p>Aspartic acid, glycine, and glutamine (C)</p> Signup and view all the answers

What are the primary nitrogen sources for pyrimidine synthesis?

<p>Aspartic acid and glutamine (B)</p> Signup and view all the answers

What is the primary function of proteolytic enzymes in the context of protein digestion?

<p>To break peptide bonds, yielding di- and tripeptides and individual amino acids. (D)</p> Signup and view all the answers

In amino acid degradation, what is the primary role of transamination?

<p>To transfer the amino group of an amino acid to another molecule, typically α-ketoglutarate. (B)</p> Signup and view all the answers

Which molecule serves as a primary acceptor of amino groups during transamination, leading to the formation of glutamate?

<p>α-Ketoglutarate (D)</p> Signup and view all the answers

What is the direct product of oxidative deamination?

<p>Free ammonia (NH4+) (A)</p> Signup and view all the answers

Which of the following statements accurately describes the direction of the glutamate dehydrogenase (Glu DH) reaction?

<p>The reaction is largely determined by the relative amounts of glutamate, $\alpha$-Ketoglutarate, ammonia, and coenzymes. (C)</p> Signup and view all the answers

What is the significance of the urea cycle in the context of amino acid metabolism?

<p>It converts toxic ammonia into urea, which is then excreted. (B)</p> Signup and view all the answers

What is the function of Alanine Aminotransferase (ALT)?

<p>It converts alanine into pyruvate (degradation) and also the reverse in muscles communicating with liver. (A)</p> Signup and view all the answers

Besides free ammonia (NH3), what is the other direct source of nitrogen incorporated into urea during the urea cycle?

<p>Aspartate (C)</p> Signup and view all the answers

Flashcards

Carbon Skeleton Metabolism

The process by which the carbon skeletons of amino acids are broken down and used for energy or biosynthesis.

α-Carbon

The central carbon atom in an amino acid, to which the amino group, carboxyl group, and side chain are attached.

Glucogenic Amino Acids

Amino acids that can be converted into glucose through gluconeogenesis.

Ketogenic Amino Acids

Amino acids that can be converted into ketone bodies.

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Both Glucogenic and Ketogenic Amino Acids

Amino acids that can be converted into both glucose and ketone bodies.

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Amino Acid Degradation

The process by which amino acids are broken down into smaller molecules that can be used for energy or biosynthesis.

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Nitrogen-containing Compound Synthesis

The process by which nitrogen-containing compounds are synthesized from simpler molecules.

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Biogenic Amines

Organic molecules produced by the removal of the carboxyl group from amino acids. They include dopamine, norepinephrine, serotonin, histamine, and others.

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Protein Digestion

The process of breaking down proteins into smaller molecules, such as dipeptides, tripeptides, and individual amino acids, which can be absorbed into the body.

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Transamination

Refers to the transfer of an amino group from an amino acid to α-ketoglutarate, forming glutamate. This is a key step in amino acid metabolism.

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Oxidative Deamination

The removal of an amino group from glutamate, releasing free ammonia (NH3) and forming α-ketoglutarate. This process produces ammonia, which is toxic and needs to be converted into urea.

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Urea Cycle

The cycle in the liver that converts ammonia (NH3) into urea, a less toxic form of nitrogen waste that can be excreted in urine.

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Alanine Aminotransferase (ALT)

A major enzyme involved in transamination reactions, which specifically converts alanine to pyruvate and α-ketoglutarate to glutamate.

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Glucose-Alanine Cycle

The process where alanine is transported from muscles to the liver to be converted to glucose. It involves both transamination and glucose synthesis

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Aminotransferases

The specific type of aminotransferases that utilize α-ketoglutarate as an amino group acceptor, forming glutamate.

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Study Notes

Metabolism of Nitrogenous Compounds

  • Learning objectives include describing protein digestion, reactions separating amino groups, fate of carbon skeletons, glucogenic and ketogenic amino acids, biogenic amines, and examples of nitrogenous compounds.

  • Nitrogenous compounds include amino acids (proteins), biogenic amines, porphyrins, and nucleobases.

  • Amino acid metabolism: Dietary protein is degraded into amino acids, which can be used for energy or protein synthesis and used to create other N-compounds. Amino acids can be converted into keto acids and then into glucose or fat. Removal of amino groups from amino acids produces urea as a byproduct.

  • Protein digestion: Proteins start to be digested in the stomach where proteases break peptide bonds. The process continues in the small intestine with endopeptidases, separating proteins into di- and tripeptides and amino acids that can be absorbed.

  • Amino acid degradation: The process of separating amino groups from amino acids via transamination or oxidative deamination. The remaining carbon skeleton is further metabolized.

  • Amino acid degradation, separation of amino group: Transamination, transferring amino groups to another molecule such as a-Ketoglutarate. Oxidative deamination, creation of free ammonia (NH4+).

  • Formation of Glutamate: A-Ketoglutarate receives the amino group to form glutamate. Lysine and Threonine are exceptions, and some aminotransferases (transaminases) have specific substrate preferences.

  • Amino acid degradation - Aminotransferases reactions: Aminotransferases transfer amino groups from an amino acid to a-ketoglutarate to create glutamate.

  • Urea cycle: Ammonia is toxic so the body transforms it into urea, a less toxic molecule. The urea cycle incorporates ammonia and aspartate into urea to be excreted.

  • Importance of Urea Cycle: Urea is a less toxic molecule produced in the liver from ammonia. It is transported to the kidneys to be excreted.

  • Nucleotide metabolism: Nucleotides are composed of a phosphate group, a pentose sugar, and a nitrogenous base. Includes the synthesis of purines and pyrimidines that are nitrogenous bases from other small molecules.

  • Porphyrins and degradation disorders : Defects in the synthesis of porphyrins, can lead to various disorders and jaundice which is yellowing of the skin and eyes. Biogenic amines: A group of amines derived from amino acids. These include, but are not limited to histamine, serotonin, and the catecholamines (dopamine, norepinephrine and epinephrine).

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