Glycosaminoglycans,proteoglycans&glycoproteinsDENS

1. Which of the following GAGs is NOT sulfated?
   A. Chondroitin sulfate
   B. Keratan sulfate
   C. Hyaluronic acid
   D. Heparan sulfate
   

1. Answer: C. Hyaluronic acid
   Explanation: Hyaluronic acid is the only GAG that is not sulfated.

1. What is the primary function of heparin?
   A. Structural support in cartilage
   B. Anticoagulation
   C. Lubrication in synovial fluid
   D. Cell signaling
   

1. Answer: B. Anticoagulation
   Explanation: Heparin acts as an anticoagulant by inhibiting blood clotting.

1. Which enzyme deficiency causes Hurler syndrome?
   A. Iduronate sulfatase
   B. α-L-iduronidase
   C. Heparan sulfatase
   D. β-Glucuronidase
   

1. Answer: B. α-L-iduronidase
   Explanation: Hurler syndrome is caused by a deficiency of α-L-iduronidase, leading to the accumulation of dermatan sulfate and heparan sulfate.

1. What is the role of dolichol in glycoprotein synthesis?
   A. It acts as a carrier for oligosaccharides in N-linked glycosylation.
   B. It catalyzes the addition of sulfate groups to GAGs.
   C. It binds to hyaluronic acid to form proteoglycan aggregates.
   D. It degrades glycoproteins in lysosomes.
   

1. Answer: A. It acts as a carrier for oligosaccharides in N-linked glycosylation.
   Explanation: Dolichol pyrophosphate carries oligosaccharides during the synthesis of N-linked glycoproteins.

1. Which of the following is a characteristic of glycoproteins but NOT GAGs?
   A. Long, unbranched polysaccharide chains
   B. Branched oligosaccharide chains
   C. High negative charge due to sulfate groups
   D. Found exclusively in the extracellular matrix
   

1. Answer: B. Branched oligosaccharide chains
   Explanation: Glycoproteins have branched oligosaccharide chains, while GAGs have long, unbranched chains.

1. Which of the following is NOT a function of glycoproteins?
   A. Cell surface recognition
   B. Structural support
   C. Anticoagulation
   D. Lubrication
   

1. Answer: C. Anticoagulation
   Explanation: Anticoagulation is a function of heparin, a GAG, not glycoproteins.

1. What is the linkage between the oligosaccharide and protein in N-linked glycoproteins?
   A. O-glycosidic bond
   B. N-glycosidic bond
   C. Phosphodiester bond
   D. Ester bond
   

1. Answer: B. N-glycosidic bond
   Explanation: In N-linked glycoproteins, the oligosaccharide is attached to the NH-group of an asparagine side chain.

1. Which of the following is a characteristic of GAGs?
   A. Branched oligosaccharides
   B. Linear polysaccharides
   C. Neutral charge
   D. Short half-life
   

1. Answer: B. Linear polysaccharides
   Explanation: GAGs are long, unbranched polysaccharides with a repeating disaccharide unit.

1. What is the primary site of GAG synthesis?
   A. Cytosol
   B. Golgi apparatus
   C. Nucleus
   D. Mitochondria
   .

1. Answer: B. Golgi apparatus
   Explanation: GAGs are synthesized primarily in the Golgi apparatus

1. Which of the following is a symptom of I-cell disease?
   A. Mental retardation
   B. Skeletal abnormalities
   C. Corneal clouding
   D. All of the above
   

1. Answer: D. All of the above
   Explanation: I-cell disease is characterized by skeletal abnormalities, mental retardation, and corneal clouding due to incorrect targeting of lysosomal enzymes.

1. Regarding GAGs:
   A. GAGs are long, unbranched polysaccharide chains.
   B. Hyaluronic acid is sulfated.
   C. GAGs are synthesized in the cytosol.
   D. GAGs are degraded in lysosomes by acid hydrolases.
   E. Deficiencies in GAG-degrading enzymes cause mucopolysaccharidoses.

1. A. GAGs are long, unbranched polysaccharide chains. (True)
   B. Hyaluronic acid is sulfated. (False)
   C. GAGs are synthesized in the cytosol. (False)
   D. GAGs are degraded in lysosomes by acid hydrolases. (True)
   E. Deficiencies in GAG-degrading enzymes cause mucopolysaccharidoses. (True)

1. Regarding proteoglycans:
   A. Proteoglycans are composed of GAGs covalently attached to core proteins.
   B. Proteoglycan aggregates are stabilized by link proteins.
   C. Proteoglycans are synthesized in the nucleus.
   D. Proteoglycans are involved in cell signaling.
   E. Proteoglycans are only found in the extracellular matrix.

1. A. Proteoglycans are composed of GAGs covalently attached to core proteins. (True)
   B. Proteoglycan aggregates are stabilized by link proteins. (True)
   C. Proteoglycans are synthesized in the nucleus. (False)
   D. Proteoglycans are involved in cell signaling. (True)
   E. Proteoglycans are only found in the extracellular matrix. (False)

1. Regarding glycoproteins:
   A. Glycoproteins have branched oligosaccharide chains.
   B. N-linked glycoproteins are synthesized on dolichol pyrophosphate.
   C. O-linked glycoproteins are attached to asparagine residues.
   D. Glycoproteins are degraded in lysosomes.
   E. Deficiencies in glycoprotein-degrading enzymes cause oligosaccharidoses.

1. A. Glycoproteins have branched oligosaccharide chains. (True)
   B. N-linked glycoproteins are synthesized on dolichol pyrophosphate. (True)
   C. O-linked glycoproteins are attached to asparagine residues. (False)
   D. Glycoproteins are degraded in lysosomes. (True)
   E. Deficiencies in glycoprotein-degrading enzymes cause oligosaccharidoses. (True)

1. Regarding clinical conditions:
   A. Hurler syndrome is caused by a deficiency of α-L-iduronidase.
   B. I-Cell disease is caused by the inability to phosphorylate mannose residues.
   C. Hunter syndrome is an X-linked disorder.
   D. Mucopolysaccharidoses are caused by deficiencies in glycoprotein-degrading enzymes.
   E. Enzyme replacement therapy is a treatment option for some lysosomal storage diseases.

1. A. Hurler syndrome is caused by a deficiency of α-L-iduronidase. (True)
   B. I-Cell disease is caused by the inability to phosphorylate mannose residues. (True)
   C. Hunter syndrome is an X-linked disorder. (True)
   D. Mucopolysaccharidoses are caused by deficiencies in glycoprotein-degrading enzymes. (False)(GAG’s)
   E. Enzyme replacement therapy is a treatment option for some lysosomal storage diseases. (True)

Regarding Glycosaminoglycans (GAGs):
A. GAGs are highly negatively charged due to sulfate and carboxyl groups.
B. Hyaluronic acid is covalently attached to a core protein.
C. GAGs are primarily synthesized in the cytosol.
D. Keratan sulfate contains galactose instead of an acidic sugar.
E. GAGs are degraded in lysosomes by acid hydrolases.

A. GAGs are highly negatively charged due to sulfate and carboxyl groups. (True)
B. Hyaluronic acid is covalently attached to a core protein. (False)
C. GAGs are primarily synthesized in the cytosol. (False)
D. Keratan sulfate contains galactose instead of an acidic sugar. (True)
E. GAGs are degraded in lysosomes by acid hydrolases. (True)

Explanation:

• A: GAGs are negatively charged due to sulfate and carboxyl groups.

• B: Hyaluronic acid is unique because it is not covalently attached to a protein.

• C: GAGs are synthesized in the Golgi apparatus, not the cytosol.

• D: Keratan sulfate contains galactose, unlike other GAGs that contain acidic sugars.

• E: Lysosomes contain acid hydrolases that degrade GAGs.

2. Regarding Proteoglycans:
   A. Proteoglycans are formed by covalent bonding between GAGs and core proteins.
   B. Proteoglycan aggregates are stabilized by link proteins.
   C. Hyaluronic acid is a component of proteoglycan aggregates.
   D. Proteoglycans are primarily found in the nucleus.
   E. Proteoglycans play a role in cell signaling and tissue organization.

2. A. Proteoglycans are formed by covalent bonding between GAGs and core proteins. (True)
   B. Proteoglycan aggregates are stabilized by link proteins. (True)
   C. Hyaluronic acid is a component of proteoglycan aggregates. (True)
   D. Proteoglycans are primarily found in the nucleus. (False)
   E. Proteoglycans play a role in cell signaling and tissue organization. (True)

   Explanation:

   • A: Proteoglycans are formed by covalent bonding between GAGs and core proteins.

   • B: Link proteins stabilize proteoglycan aggregates.

   • C: Hyaluronic acid is a key component of proteoglycan aggregates.

   • D: Proteoglycans are found in the extracellular matrix, not the nucleus.

   • E: Proteoglycans are involved in cell signaling and tissue organization.

3. Regarding Glycoproteins:
   A. Glycoproteins have branched oligosaccharide chains.
   B. N-linked glycoproteins attach oligosaccharides to serine or threonine.
   C. Glycoproteins are synthesized in the rough endoplasmic reticulum (RER).
   D. Glycoproteins are degraded in lysosomes.
   E. Glycoproteins are involved in cell surface recognition.

3. A. Glycoproteins have branched oligosaccharide chains. (True)
   B. N-linked glycoproteins attach oligosaccharides to serine or threonine. (False)
   C. Glycoproteins are synthesized in the rough endoplasmic reticulum (RER). (True)
   D. Glycoproteins are degraded in lysosomes. (True)
   E. Glycoproteins are involved in cell surface recognition. (True)

   Explanation:

   • A: Glycoproteins often have branched oligosaccharide chains.

   • B: N-linked glycoproteins attach oligosaccharides to asparagine, not serine or threonine.

   • C: Glycoproteins are synthesized in the RER and Golgi apparatus.

   • D: Lysosomal enzymes degrade glycoproteins.

   • E: Glycoproteins play a role in cell surface recognition and antigenicity.

Regarding Mucopolysaccharidoses (MPS):
A. MPS are caused by deficiencies in lysosomal enzymes.
B. Hurler syndrome is caused by a deficiency of α-L-iduronidase.
C. MPS patients have normal GAG degradation.
D. Enzyme replacement therapy is a treatment option for MPS.
E. MPS leads to the accumulation of partially degraded GAGs in lysosomes.

A. MPS are caused by deficiencies in lysosomal enzymes. (True)
B. Hurler syndrome is caused by a deficiency of α-L-iduronidase. (True)
C. MPS patients have normal GAG degradation. (False)
D. Enzyme replacement therapy is a treatment option for MPS. (True)
E. MPS leads to the accumulation of partially degraded GAGs in lysosomes. (True)

Explanation:

• A: MPS are caused by deficiencies in lysosomal enzymes.

• B: Hurler syndrome is caused by a deficiency of α-L-iduronidase.

• C: MPS patients have impaired GAG degradation due to enzyme deficiencies.

• D: Enzyme replacement therapy is used to treat some types of MPS.

• E: MPS results in the accumulation of partially degraded GAGs in lysosomes.

5. Regarding Synthesis and Degradation:
   A. GAGs are synthesized in the Golgi apparatus.
   B. Sulfation of GAGs occurs after monosaccharide incorporation.
   C. Lysosomal degradation of GAGs requires acid hydrolases.
   D. Glycoproteins are synthesized on free ribosomes in the cytosol.
   E. I-cell disease is caused by incorrect targeting of lysosomal enzymes.

5. A. GAGs are synthesized in the Golgi apparatus. (True)
   B. Sulfation of GAGs occurs after monosaccharide incorporation. (True)
   C. Lysosomal degradation of GAGs requires acid hydrolases. (True)
   D. Glycoproteins are synthesized on free ribosomes in the cytosol. (False)
   E. I-cell disease is caused by incorrect targeting of lysosomal enzymes. (True)

   Explanation:

   • A: GAGs are synthesized in the Golgi apparatus.

   • B: Sulfation occurs after monosaccharides are incorporated into GAG chains.

   • C: Lysosomal degradation of GAGs requires acid hydrolases.

   • D: Glycoproteins are synthesized on ribosomes attached to the RER, not free ribosomes.

   • E: I-cell disease results from incorrect targeting of lysosomal enzymes due to a lack of mannose phosphorylation.

1. What is the role of GAGs in the extracellular matrix (ECM)?
   

1. Answer: GAGs provide hydration, flexibility, and structural support to the ECM. They also act as a molecular sieve, influencing the movement of materials through the ECM.
   Explanation: GAGs bind large amounts of water, creating a gel-like matrix that offers resilience and lubrication.

1. How are proteoglycan aggregates formed?
   

1. Answer: Proteoglycan aggregates are formed by the non-covalent association of proteoglycan monomers with hyaluronic acid, stabilized by link proteins.
   Explanation: The interaction is primarily ionic, not covalent, and involves the core protein of proteoglycans and hyaluronic acid.

1. What is the difference between N-linked and O-linked glycoproteins?
   

1. Answer: N-linked glycoproteins have oligosaccharides attached to the NH-group of asparagine, while O-linked glycoproteins have oligosaccharides attached to the OH-group of serine or threonine.
   Explanation: The type of glycosidic linkage determines the classification of glycoproteins.

1. What is the significance of lysosomal degradation in GAG metabolism?
   

1. Answer: Lysosomal degradation is crucial for breaking down GAGs. Deficiencies in lysosomal enzymes lead to the accumulation of GAGs, causing mucopolysaccharidoses (MPS).
   Explanation: Lysosomes contain acid hydrolases that degrade GAGs, and enzyme deficiencies result in storage diseases.

1. What is the function of heparin in the body?
   

1. Answer: Heparin acts as an anticoagulant by inhibiting blood clotting. It is found in mast cells, particularly in the liver, lungs, and skin.
   Explanation: Heparin is an intracellular GAG that plays a key role in preventing blood clot formation.