Biochemistry of Glycosaminoglycans and PAPS
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What is the primary role of 3’-Phosphoadenosyl-5’-Phosphosulfate (PAPS) in metabolic processes?

  • It serves as a sulfur donor in glycosphingolipid synthesis. (correct)
  • It acts as an energy source for cellular respiration.
  • It is a critical component of DNA synthesis.
  • It facilitates the hydrolysis of polysaccharides.

    • Which enzyme is responsible for sulfation of carbohydrate chains?

  • Sulfotransferase (correct)
  • Sulfide reductase
  • Glucuronic acid transferase
  • Uronosyl 5-Epimerase

    • A defect in the process of sulfation may lead to which of the following disorders?

  • Autosomal recessive disorders affecting skeletal development (correct)
  • Cardiovascular diseases
  • Diabetes mellitus
  • Arthritis

    • What type of reaction does Uronosyl 5-Epimerase catalyze?

    <p>Epimerization of D-sugar to L-sugar</p> Signup and view all the answers

    In which cellular organelle does core protein synthesis occur?

    <p>Endoplasmic reticulum (ER)</p> Signup and view all the answers

    What occurs to core proteins as they move through the ER?

    <p>They are glycosylated by membrane-bound transferases.</p> Signup and view all the answers

    What is the primary function of glucuronic acid in sulfation?

    <p>It provides sulfate through PAPS.</p> Signup and view all the answers

    What type of biochemical disorder can arise from a defect in glucuronic acid incorporation?

    <p>Skeletal system disorders</p> Signup and view all the answers

    Which of the following statements about 3’-Phosphoadenosyl-5’-Phosphosulfate (PAPS) is NOT true?

    <p>PAPS is synthesized without the involvement of glucuronic acid.</p> Signup and view all the answers

    Which of the following sugar nucleotides serves as a precursor for glycoproteins?

    <p>UDP-galactose</p> Signup and view all the answers

    What type of amino acid R-groups are specifically targeted for glycosylation by oligosaccharides?

    <p>Serine and Threonine</p> Signup and view all the answers

    Which of the following statements concerning UDP-N-acetylgalactosamine is true?

    <p>It donates sugars to growing carbohydrate chains.</p> Signup and view all the answers

    What is a common fate of N-linked glycoproteins within the cell?

    <p>They may be translocated to lysosomes.</p> Signup and view all the answers

    How are GDP-fucose and GDP-mannose related in terms of biosynthesis?

    <p>GDP-fucose is synthesized from GDP-mannose.</p> Signup and view all the answers

    What is the significance of the negative charge of CMP-NANA at physiological pH?

    <p>It aids in sugar donation to carbohydrate chains.</p> Signup and view all the answers

    Which of the following is NOT a sugar nucleotide involved in glycoprotein synthesis?

    <p>UDP-xylose</p> Signup and view all the answers

    In what cellular compartment does the glycosylation process occur for proteins synthesized on the ER?

    <p>Lumen of ER</p> Signup and view all the answers

    Which type of glycosylation involves the transfer of N-acetylgalactosamine from UDP-N-galactosamine?

    <p>O-Linked Glycosylation</p> Signup and view all the answers

    What structural role do carbohydrates play in glycoproteins?

    <p>They provide recognition signals for molecular interactions.</p> Signup and view all the answers

    What type of bond is formed between xylose and the hydroxyl group of serine?

    <p>O-glycosidic bond</p> Signup and view all the answers

    The alternating residues in bacterial cell walls consist mainly of which two components?

    <p>N-acetylmuramic acid and N-acetylglucosamine</p> Signup and view all the answers

    Which molecule cleaves the glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine?

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

    What is the role of penicillin in relation to peptidoglycan?

    <p>Inhibit formation of cross-links</p> Signup and view all the answers

    What happens in glycoprotein storage diseases due to enzyme deficiency?

    <p>Accumulation of partially degraded structures</p> Signup and view all the answers

    Lysosomal hydrolytic enzymes are typically characterized as which of the following?

    <p>Exoenzymes specific for the removal of one component</p> Signup and view all the answers

    What is the significance of the low optimum pH (pH 5) in lysosomes?

    <p>It enhances the activity of lysosomal enzymes.</p> Signup and view all the answers

    Which process begins the synthesis of the carbohydrate chain in lysosomes?

    <p>Transfer of a xylose from UDP-xylose to a hydroxyl group.</p> Signup and view all the answers

    What is the half-life of hyaluronic acid within lysosomes?

    <p>3 days</p> Signup and view all the answers

    Which of the following statements about keratan sulfate is correct?

    <p>It has a half-life of 120 days.</p> Signup and view all the answers

    What occurs after a vesicle containing phagocytosed material fuses with a lysosome?

    <p>It forms a phagolysosome for degradation.</p> Signup and view all the answers

    Which enzyme is responsible for catalyzing the transfer of xylose in carbohydrate synthesis?

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

    What type of enzymes are found in lysosomes?

    <p>Hydrolytic enzymes known as acid hydrolases.</p> Signup and view all the answers

    How does sulfation occur during the synthesis of the carbohydrate chain?

    <p>After the monosaccharide has been incorporated into the chain.</p> Signup and view all the answers

    In what condition are lysosomal enzymes active?

    <p>In acidic environments around pH 5.</p> Signup and view all the answers

    What is the role of acid hydrolases in lysosomes?

    <p>To break down materials brought into the lysosome.</p> Signup and view all the answers

    What is required for the synthesis of N-Linked glycosides?

    <p>Dolichol and dolichol pyrophosphate</p> Signup and view all the answers

    Where does the synthesis of dolichol-linked oligosaccharides occur?

    <p>Lumen of the Endoplasmic Reticulum (ER)</p> Signup and view all the answers

    Which of the following sugars is NOT part of the oligosaccharide constructed on dolichol?

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

    What characterizes the final processing of N-Linked oligosaccharides?

    <p>Removal of mannosyl and glycosyl residues followed by various sugar additions</p> Signup and view all the answers

    Which of the following is a characteristic of conditions caused by defects in N-Linked glycosylation?

    <p>Restricted joint movement</p> Signup and view all the answers

    What happens to the oligosaccharide during its transfer from dolichol to protein?

    <p>It is linked to an asparagine side group</p> Signup and view all the answers

    Which glycosaminoglycan (GAG) is not covalently attached to protein to form proteoglycans?

    <p>Hyaluronic acid</p> Signup and view all the answers

    Which feature is least likely to be associated with N-Linked glycosylation disorders?

    <p>Enhancement of motor skills</p> Signup and view all the answers

    What does the removal of specific residues during N-Linked oligosaccharide processing primarily lead to?

    <p>Modification of protein functions</p> Signup and view all the answers

    Which of the following substances is most directly linked through a pyrophosphate linkage to the oligosaccharide during its synthesis?

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

    Study Notes

    3’-Phosphoadenosyl-5’-Phosphosulfate (PAPS)

    • PAPS is a molecule of AMP with a sulfate group attached to the 5’-phosphate.
    • Synthesis occurs after D-glucuronic acid is incorporated into the carbohydrate chain.
    • Acts as a source of sulfate and a sulfur donor in glycosphingolipid synthesis.

    Sulfotransferase and Sulfation

    • Sulfotransferase facilitates sulfation of carbohydrate chains at specific sites.
    • Defects in sulfation can lead to autosomal recessive disorders affecting skeletal system development.

    Core Protein Synthesis

    • Proteins synthesized in the endoplasmic reticulum (ER) are glycosylated by membrane-bound transferases.

    Degradation of Glycosaminoglycans (GAGs)

    • GAG degradation occurs in lysosomes, containing hydrolytic enzymes active at pH 5, known as acid hydrolases.
    • Low pH protects the cell by preventing lysosomal enzymes from functioning in neutral cytosol.
    • GAGs have varying half-lives: hyaluronic acid (3 days), chondroitin and dermatan sulfate (10 days), keratan sulfate (120 days).

    Synthesis of Carbohydrate Chain

    • Initiated by transferring xylose from UDP-xylose to serine/threonine hydroxyl group, catalyzed by xylosyltransferase.
    • Sequential addition of sugars occurs, involving alternating acidic and amino sugars and conversion of D-glucuronyl to L-iduronyl residues.

    Addition of Sulfate Groups

    • Sulfation occurs after monosaccharides are incorporated into the growing carbohydrate chain.

    Phagocytosis of GAGs

    • GAGs are phagocytosed into a vesicle that fuses with the lysosome, forming a phagolysosome for degradation.

    Sugar Nucleotides

    • Serve as precursors for glycoprotein carbohydrate components, including UDP-glucose, UDP-galactose, UDP-N-acetylglucosamine, and others such as GDP-mannose.

    Glycosylation of Proteins

    • Oligosaccharides are attached to specific amino acid R-groups based on protein's 3D structure.
    • Synthesis of O-linked glycosides occurs in the ER, transferring N-acetylgalactosamine onto seryl or threonyl R-groups.

    Synthesis of N-Linked Glycosides

    • Occurs in the ER and Golgi apparatus, requiring dolichol and dolichol pyrophosphate.
    • Final processing involves removal of initial sugar residues and addition of various sugars.

    Structure of Proteoglycans

    • All GAGs, except hyaluronic acid, attach covalently to proteins, forming proteoglycan monomers through O-glycosidic bonds to serine residues.

    Bacterial Cell Wall Polysaccharides

    • Comprise alternating β (1→4)-linked N-acetylmuramic acid and N-acetylglucosamine residues, forming a mesh framework through cross-linking tetrapeptides.

    Enzymatic Actions

    • Lysozyme cleaves glycosidic bonds in peptidoglycan, aiding in degradation.
    • Penicillin inhibits cross-link formation in peptidoglycan, serving as an antibiotic.

    Lysosomal Glycoprotein Degradation

    • Lysosomal enzymes remove specific components of glycoproteins sequentially, primarily as exoenzymes.

    Glycoprotein Storage Diseases

    • Result from deficiencies in degradative enzymes, causing accumulation of partially degraded structures in lysosomes.
    • Symptoms correlate with enzyme deficiencies seen in mucopolysaccharidoses and glycolipid degradation issues.

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    Description

    This quiz covers the biochemistry of 3’-Phosphoadenosyl-5’-Phosphosulfate (PAPS), its role in sulfation and glycosaminoglycan (GAG) degradation. Explore the mechanisms of sulfotransferase, synthesis of core proteins, and the effects of sulfation defects on skeletal development.

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