Question 1

Which of the following best explains why glycosaminoglycans (GAGs) contribute to the resilience and compressibility of synovial fluid in joints?

Accepted Answer

GAGs are highly negatively charged, attracting water and forming a gel-like matrix that resists compression and springs back when pressure is released.

Question 2

A patient is diagnosed with a mucopolysaccharidosis due to a deficiency in a lysosomal hydrolase. Which of the following is the most likely biochemical consequence?

Accepted Answer

Accumulation of partially degraded glycosaminoglycans in lysosomes.

Question 3

Which of the following statements about the structure of glycosaminoglycans (GAGs) is CORRECT?

Accepted Answer

GAGs are unbranched heteropolysaccharide chains with repeating disaccharide units of an acidic sugar and an amino sugar.

Question 4

During the synthesis of glycosaminoglycans, which molecule donates the sulfate group for sulfation of the growing chain?

Accepted Answer

3'-phosphoadenosyl-5'-phosphosulfate (PAPS)

Question 5

Which of the following best describes the role of proteoglycan aggregates in cartilage?

Accepted Answer

They consist of proteoglycan monomers non-covalently associated with hyaluronic acid, providing compressive strength and flexibility.

Question 6

A mutation in the gene encoding iduronate sulfatase leads to the accumulation of dermatan sulfate and heparan sulfate. Which disease is most likely associated with this deficiency?

Accepted Answer

Hunter syndrome

Question 7

Which of the following steps occurs FIRST in the synthesis of an O-linked glycoprotein?

Accepted Answer

Addition of N-acetylgalactosamine (GalNAc) to the hydroxyl group of a serine or threonine residue.

Question 8

Which of the following best distinguishes glycoproteins from proteoglycans?

Accepted Answer

Proteoglycans contain a higher percentage of carbohydrate (up to 95%) and have long, linear GAG chains, while glycoproteins have shorter, often branched oligosaccharides.

Question 9

Which of the following is required for the activation of sialic acid (N-acetylneuraminic acid, NANA) before its incorporation into glycoproteins?

Accepted Answer

It must be activated to CMP-NANA by reacting with CTP.

Question 10

A researcher is studying the biosynthesis of glycosaminoglycans and observes that the process is disrupted in the Golgi apparatus. Which of the following steps is most likely affected?

Accepted Answer

Elongation of the polysaccharide chain by sequential addition of alternating acidic and amino sugars from their UDP derivatives.

Question 11

Which of the following best explains why GAGs are highly negatively charged at physiological pH?

Accepted Answer

Their repeating disaccharide units include acidic sugars with carboxyl groups and often sulfate groups.

Question 12

Which of the following is the correct sequence of events in the lysosomal degradation of glycosaminoglycans?

Accepted Answer

Endocytosis of GAGs, fusion with lysosome, sequential removal of terminal sugars and sulfate groups by acid hydrolases.

Question 13

Which of the following best describes the function of the pentasaccharide core in N-linked glycoproteins?

Accepted Answer

It serves as the site for the initial attachment of the oligosaccharide to the asparagine residue of the protein.

Question 14

A defect in the enzyme UDP-glucose dehydrogenase would most directly impair which of the following processes?

Accepted Answer

Synthesis of UDP-glucuronic acid required for GAG biosynthesis and glucuronidation.

Question 15

Which of the following statements about the degradation of glycoproteins is TRUE?

Accepted Answer

Acid hydrolases in lysosomes remove sugar residues in the reverse order of their incorporation.

Question 16

Which of the following best describes the initial step in the synthesis of a proteoglycan monomer?

Accepted Answer

Attachment of a xylose residue from UDP-xylose to the hydroxyl group of a serine residue in the core protein.

Question 17

A patient presents with hepatosplenomegaly and developmental delay. Laboratory analysis reveals accumulation of heparan sulfate and dermatan sulfate. Which enzyme deficiency is most likely responsible?

Accepted Answer

Alpha-L-iduronidase

Question 18

Which of the following is a key difference between N-linked and O-linked glycoprotein synthesis?

Accepted Answer

N-linked glycoproteins involve the transfer of a preformed oligosaccharide from dolichol to asparagine, while O-linked glycoproteins are synthesized by sequential addition of sugars to serine or threonine.

Glycosaminoglycans, Proteoglycans, and Glycoproteins: Structure, Synthesis, and Function

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