Amino Acids and Metabolism Quiz
47 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which amino acids play key roles in the transport and distribution of amino groups in mammals?

  • Lysine, Valine, Glutamine, Alanine
  • Serine, Threonine, Glutamate, Aspartate
  • Cysteine, Methionine, Arginine, Proline
  • Alanine, Glutamate, Glutamine, Aspartate (correct)

    • What is the primary reason that amino acids undergo oxidative degradation?

  • When amino acids are released from protein turnover and not required for synthesis (correct)
  • When there is insufficient carbohydrate availability for energy
  • To produce essential lipids necessary for cell membranes
  • When amino acids are needed for energy production

    • Which amino acid does not contribute to gluconeogenesis when needed?

  • Lysine (correct)
  • Glutamine
  • Serine
  • Alanine

    • Which principle emphasizes the intertwined nature of metabolic pathways for amino acid catabolism?

    <p>Principle 3: Intertwined metabolic pathways</p> Signup and view all the answers

    What is the role of the urea cycle in mammals?

    <p>To excrete excess amino groups safely</p> Signup and view all the answers

    Which cofactors are involved in the key step of amino group separation during amino acid degradation?

    <p>Pyridoxal phosphate</p> Signup and view all the answers

    Why are leucine and lysine distinct from other amino acids regarding gluconeogenesis?

    <p>They cannot be converted into glucose precursors</p> Signup and view all the answers

    Which of the following statements about the breakdown of amino acids is true?

    <p>All amino acids can be oxidized to generate ATP.</p> Signup and view all the answers

    What is the primary function of pyridoxal phosphate (PLP) in amino acid catabolism?

    <p>It accepts amino groups during transamination reactions.</p> Signup and view all the answers

    Which of the following is NOT a reaction facilitated by pyridoxal phosphate?

    <p>Hydrolysis</p> Signup and view all the answers

    How is pyridoxal phosphate (PLP) linked to the enzyme it acts upon?

    <p>Via an aldimine (Schiff base) linkage</p> Signup and view all the answers

    What happens to the aldimine linkage in the PLP-catalyzed reactions?

    <p>It is replaced by the amino group of the amino acid.</p> Signup and view all the answers

    Which statement accurately describes pyridoxal phosphate's role in amino acid catabolism?

    <p>PLP primarily aids in amino group metabolism.</p> Signup and view all the answers

    Which form of pyridoxal phosphate accepts amino groups?

    <p>Pyridoxal phosphate (aldehyde form)</p> Signup and view all the answers

    What are the two broad parts involved in amino acid catabolism?

    <p>Amino group metabolism and carbon skeleton breakdown</p> Signup and view all the answers

    Which statement about the use of pyridoxal phosphate is false?

    <p>It is only required for transaminases.</p> Signup and view all the answers

    Which of the following pancreatic enzymes is stimulated by cholecystokinin?

    <p>Trypsinogen</p> Signup and view all the answers

    What is the optimal pH range for pancreatic peptidases?

    <p>7 to 8</p> Signup and view all the answers

    Which enzyme is activated by autocatalytic cleavage at low pH?

    <p>Pepsin</p> Signup and view all the answers

    Which of the following describes the absorption of amino acids in the small intestine?

    <p>They enter blood capillaries in the intestinal villi.</p> Signup and view all the answers

    What role does gastrin play in dietary protein digestion?

    <p>Stimulates secretion of hydrochloric acid and pepsinogen</p> Signup and view all the answers

    What is the primary function of glutamate dehydrogenase in amino acid metabolism?

    <p>It deaminates glutamate to α-ketoglutarate.</p> Signup and view all the answers

    Which type of enzymes are primarily activated in the upper gastrointestinal tract for protein metabolism?

    <p>Peptidases</p> Signup and view all the answers

    What is the consequence of dietary protein entering the stomach?

    <p>Stimulates the gastric mucosa to secrete gastrin</p> Signup and view all the answers

    Which amino acids are primarily involved in the transport and distribution of amino groups?

    <p>Alanine, glutamate, glutamine, and aspartate.</p> Signup and view all the answers

    Which pro-enzyme is not specifically stimulated by cholecystokinin?

    <p>Pepsinogen</p> Signup and view all the answers

    What signaling molecule negatively modulates the activity of glutamate dehydrogenase?

    <p>GTP, indicating high levels of α-ketoglutarate.</p> Signup and view all the answers

    How do metabolic pathways for amino acid catabolism relate to other pathways?

    <p>They are intricately intertwined with other metabolic pathways.</p> Signup and view all the answers

    What happens to free ammonia produced during amino acid metabolism?

    <p>It must be safely excreted through the urea cycle.</p> Signup and view all the answers

    What form of nitrogen excretion is characteristic of most terrestrial animals, including humans?

    <p>Urea</p> Signup and view all the answers

    Which amino acid is directly converted to pyruvate in nitrogen metabolism?

    <p>Alanine</p> Signup and view all the answers

    What is the primary action of gastrin in the digestive process?

    <p>Stimulate secretion of HCl and pepsinogen</p> Signup and view all the answers

    Which hormone is responsible for stimulating the release of bicarbonate from the pancreas?

    <p>Secretin</p> Signup and view all the answers

    What is the role of enteropeptidase in digestion?

    <p>Converts trypsinogen to trypsin</p> Signup and view all the answers

    Which of the following amino acids is NOT involved in easily converting to citric acid cycle intermediates?

    <p>Tyrosine</p> Signup and view all the answers

    What pancreatic zymogen is activated to produce chymotrypsin?

    <p>Chymotrypsinogen</p> Signup and view all the answers

    Which type of animals primarily excrete nitrogen as ammonia?

    <p>Ammonotelic animals</p> Signup and view all the answers

    What is the function of the pancreatic trypsin inhibitor?

    <p>Protects the pancreas from self-digestion</p> Signup and view all the answers

    In nitrogen metabolism, which intermediate does aspartate convert to?

    <p>Oxaloacetate</p> Signup and view all the answers

    Which statement regarding the anemia associated with vitamin B12 deficiency is true?

    <p>It's termed megaloblastic anemia due to the presence of megaloblasts.</p> Signup and view all the answers

    What role does tetrahydrobiopterin play in amino acid catabolism?

    <p>It participates in oxidation reactions.</p> Signup and view all the answers

    Which amino acids can be converted into pyruvate?

    <p>Alanine, tryptophan, cysteine, serine, glycine, and threonine.</p> Signup and view all the answers

    What is the immediate metabolic fate of pyruvate after its formation from serine?

    <p>Conversion to acetyl-CoA for oxidation via the citric acid cycle.</p> Signup and view all the answers

    Which of the following amino acids cannot contribute to gluconeogenesis?

    <p>Leucine</p> Signup and view all the answers

    What is the function of serine dehydratase in amino acid metabolism?

    <p>It catalyzes the conversion of serine to pyruvate, removing amino groups.</p> Signup and view all the answers

    Which of the following correctly identifies the key step in amino acid degradation?

    <p>Separation of the α-amino group from the carbon skeleton.</p> Signup and view all the answers

    What is the main feature of metabolic pathways for amino acid catabolism?

    <p>They are elaborately intertwined with other catabolic and anabolic pathways.</p> Signup and view all the answers

    Study Notes

    Amino Acid Oxidation and Urea Production

    • Amino acid catabolism has two main parts: one involving amino groups and the other involving carbon skeletons.
    • All amino acid degradation pathways involve a key step using pyridoxal phosphate (a cofactor).
    • In this step, the amino group is separated from the carbon skeleton and channeled into pathways for amino group metabolism.
    • The carbon skeletons are broken down into citric acid cycle intermediates.
    • Free ammonia is toxic, so excess amino groups need safe excretion. The urea cycle in mammals serves this purpose.
    • Each amino acid has a unique catabolic fate. All can be oxidized to generate ATP. All but leucine and lysine can contribute to gluconeogenesis.
    • Key amino acids involved in nitrogen transport and distribution include alanine, glutamate, glutamine, and aspartate. These are present in high concentrations in mammalian tissues and are readily converted to citric acid cycle intermediates.
    • Metabolic pathways are not isolated; their processes are interwoven with other catabolic and anabolic pathways.

    Metabolic Circumstances of Amino Acid Oxidation

    • Amino acids undergo oxidative degradation when:
      • amino acids released from protein turnover are not needed for new protein synthesis
      • ingested amino acids exceed the body's needs for protein synthesis
      • cellular proteins are used for fuel when carbohydrates are unavailable or improperly utilized

    Metabolic Fates of Amino Groups

    • Glutamate and glutamine channel amino groups to a single excretory product
    • Free ammonia is toxic
    • Excess amino groups must be excreted safely. In mammals, the urea cycle serves this purpose.

    Ammonotelic, Ureotelic, and Uricotelic Animals

    • Ammonotelic animals excrete amino nitrogen as ammonia (most aquatic species).
    • Ureotelic animals excrete amino nitrogen as urea (most terrestrial animals, including humans).
    • Uricotelic animals excrete amino nitrogen as uric acid (birds and reptiles).

    Dietary Protein Degradation

    • Protein degradation in the gastrointestinal tract involves several hormones and enzymes:
      • Gastrin: a hormone secreted when dietary protein enters the stomach, stimulating the secretion of HCI and pepsinogen.
      • Pepsinogen: a zymogen converted to active pepsin by autocatalytic cleavage at low pH.
      • Secretin: a hormone secreted into the blood in response to low pH in the small intestine, stimulating the pancreas to secrete bicarbonate into the small intestine.
      • Pancreatic proteases: several proteases (e.g., trypsinogen, chymotrypsinogen) are stimulated by cholecystokinin, secreted into the blood in response to peptides in the small intestine.
    • These processes break down dietary protein to amino acids.
    • The intestinal mucosa absorbs free amino acids and transports them into the blood. They travel to the liver.

    Acute Pancreatitis

    • Acute pancreatitis is caused by obstruction of the pathway for pancreatic secretions to enter the intestine.
    • Premature conversion of zymogens to active forms leads to self-digestion of the pancreas.

    Pyridoxal Phosphate (PLP)

    • PLP is the coenzyme form of pyridoxine or vitamin B6.
    • It serves as a prosthetic group for all aminotransferases.
    • PLP carries amino groups at the active site.

    Transamination Reactions

    • Transamination reactions transfer the α-amino group to the α-carbon atom of α-ketoglutarate.
    • The resulting product is an α-keto acid analog of the amino acid.
    • Reactions are freely reversible (ΔG' ~ 0 kJ/mol).
    • The reactions effectively collect amino groups from many amino acids in the form of L-glutamate.

    Urea Cycle

    • The urea cycle is the pathway by which ammonia, deposited in hepatocyte mitochondria, is converted to urea.

    • Urea is then excreted into the urine.

    • Enzymes are clustered within metabolons.

    • The urea cycle takes place in two cellular compartments.

    Urea Cycle Enzymatic Steps

    • Carbamoyl phosphate synthetase I: catalyzes the formation of carbamoyl phosphate from NH4+ and CO2 (requires 2 ATP). Takes place in the mitochondrial matrix.

    • Ornithine transcarbamoylase:catalyzes the formation of citrulline and P₁ from ornithine and carbamoyl phosphate. Takes place in the mitochondrial matrix.

    • Argininosuccinate synthetase:catalyzes the condensation of the amino group of aspartate and the ureido group of citrulline to form argininosuccinate. (requires ATP; uses a citrullyl-AMP intermediate) Takes place in the cytosol.

    • Argininosuccinase: catalyzes the reversible cleavage of argininosuccinate to form arginine and fumarate. Fumarate is converted to malate and joins the pool of citric acid cycle intermediates. Takes place in the cytosol.

    • Arginase: catalyzes the cleavage of arginine to form urea and ornithine. Ornithine is transported into the mitochondrion to initiate another round of the cycle in the mitochondrial matrix.

    Glutamine

    • Glutamine synthetase catalyzes the combination of free ammonia with glutamate to yield glutamine (requires ATP).
    • Critical for transporting toxic ammonia to the liver.
    • Glutaminase catalyzes the conversion of glutamine back to glutamate and NH4+.

    Alanine

    • Alanine aminotransferase interconverts pyruvate and alanine.
    • An important molecule in the transport of amino groups to the liver.

    Glucose-Alanine Cycle

    • A pathway by which alanine carries ammonia and the carbon skeleton of pyruvate to the liver.
    • Ammonia is excreted, and pyruvate is used to produce glucose that then returns to the muscle.

    Amino Acid Degradation to Pyruvate

    • Six amino acids (alanine, tryptophan, cysteine, serine, glycine, and threonine) are converted to pyruvate.
    • Pyruvate can either be converted to:
      • Acetyl-CoA for oxidation via the citric acid cycle.
      • Oxaloacetate to enter gluconeogenesis

    Serine Dehydratase

    • Serine dehydratase catalyzes the conversion of serine to pyruvate.
    • It removes both the β-hydroxyl and α-amino groups of serine.
    • This reaction is a pyridoxal phosphate-dependent reaction.

    Glycine

    • Glycine can be degraded via serine hydroxymethyltransferase (requires tetrahydrofolate and pyridoxal phosphate).
    • Glycine can be degraded via glycine cleavage enzyme (requires tetrahydrofolate).
    • Glycine can be degraded via D-amino acid oxidase.

    Genetic Defects in Amino Acid Metabolism

    • Many amino acids are neurotransmitters or precursors or antagonists of neurotransmitters.
    • Genetic defects in amino acid metabolism can lead to defective neural development and intellectual deficits.

    Phenylketonuria (PKU)

    • A disease caused by a genetic defect in phenylalanine hydroxylase.
    • Most common cause of elevated phenylalanine levels in the blood.
    • Treated with dietary intervention.

    Phenylalanine Hydroxylase

    • Phenylalanine hydroxylase requires tetrahydrobiopterin as a cofactor.
    • It is a mixed-function oxygenase, catalyzing hydroxylation of phenylalanine.

    Tetrahydrobiopterin

    • Tetrahydrobiopterin (a cofactor) carries electrons from NADPH to O2.
    • Dihydrobiopterin reductase catalyzes the reduction of dihydrobiopterin to tetrahydrobiopterin.

    Alternative Pathways for Phenylalanine Catabolism in PKU

    • Aminotransferase catalyzes the transamination of phenylalanine with pyruvate to form phenylpyruvate.
    • Phenylpyruvate is either decarboxylated or reduced.

    Maple Syrup Urine Disease

    • A disease caused by defects in branched-chain α-keto acid dehydrogenase complex.
    • Isoleucine, leucine and valine cannot be degraded in the liver.
    • Results in accumulation of α-keto acids.
    • Treated with controlled diets.

    Asparagine and Aspartate

    • Asparagine and aspartate are degraded to the citric acid cycle intermediate oxaloacetate.
    • Asparaginase catalyzes the hydrolysis of asparagine to aspartate.
    • Aspartate aminotransferase catalyzes the transamination of aspartate with α-ketoglutarate, yielding glutamate and oxaloacetate.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Chapter 18 Slides PDF

    Description

    Test your knowledge on the roles of amino acids in mammalian metabolism. This quiz covers key concepts such as amino acid transport, gluconeogenesis, and the significance of the urea cycle. Dive deep into the biochemistry of amino group degradation and the functions of cofactors like pyridoxal phosphate (PLP).

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser