Glycosaminoglycans and Glycoproteins Lecture Notes

These flashcards cover key concepts related to glycosaminoglycans and glycoproteins, focusing on their structure, function, and related diseases.

What are glycosaminoglycans (GAGs)?

Long, negatively charged, unbranched heteropolysaccharide chains composed of repeating disaccharide units.

What are the acidic sugars found in glycosaminoglycans?

Glucuronic acid and Iduronic acid.

What role does mannose-6-phosphate play in lysosomal targeting?

It targets N-linked glycoproteins to lysosomes for degradation.

What defines mucopolysaccharidoses?

A group of disorders caused by deficiencies in the enzymes that degrade glycosaminoglycans.

What are the clinical features of Hurler syndrome?

Coarse facial features, corneal clouding, skeletal abnormalities, hepatosplenomegaly, and severe intellectual disability.

How are proteoglycans structured?

Proteoglycans are formed by covalent linkage of GAGs to a core protein, with multiple GAG chains attached.

What distinguishes glycoproteins from proteoglycans?

Glycoproteins have shorter, often branched carbohydrate chains, while proteoglycans have long, unbranched chains.

What happens in I-cell disease?

Hydrolytic enzymes are absent from lysosomes, leading to accumulation of substances destined for degradation.

What is the significance of sulfation in GAGs?

Sulfation adds negative charges, contributing to the structural properties and functions of GAGs.

What are the main functions of glycoproteins?

Cell surface receptors, antibodies, plasma proteins, enzymes, and hormones.

What are glycosaminoglycans (GAGs)?

Long, negatively charged, unbranched heteropolysaccharide chains composed of repeating disaccharide units.

What are the acidic sugars found in glycosaminoglycans?

Glucuronic acid and Iduronic acid.

What role does mannose-6-phosphate play in lysosomal targeting?

It targets N-linked glycoproteins to lysosomes for degradation.

What defines mucopolysaccharidoses?

A group of disorders caused by deficiencies in the enzymes that degrade glycosaminoglycans.

What are the clinical features of Hurler syndrome?

Coarse facial features, corneal clouding, skeletal abnormalities, hepatosplenomegaly, and severe intellectual disability.

How are proteoglycans structured?

Proteoglycans are formed by covalent linkage of GAGs to a core protein, with multiple GAG chains attached.

What distinguishes glycoproteins from proteoglycans?

Glycoproteins have shorter, often branched carbohydrate chains, while proteoglycans have long, unbranched chains.

What happens in I-cell disease?

Hydrolytic enzymes are absent from lysosomes, leading to accumulation of substances destined for degradation.

What is the significance of sulfation in GAGs?

Sulfation adds negative charges, contributing to the structural properties and functions of GAGs.

What are the main functions of glycoproteins?

Cell surface receptors, antibodies, plasma proteins, enzymes, and hormones.

What are some major types of glycosaminoglycans (GAGs)?

Hyaluronic acid, chondroitin sulfate, keratan sulfate, dermatan sulfate, and heparin/heparan sulfate.

What is unique about hyaluronic acid among GAGs?

It is the only GAG not covalently linked to a protein (not forming proteoglycans) and is not sulfated.

What is the primary defect in I-cell disease?

A deficiency in N-acetylglucosaminyl-1-phosphotransferase, which is responsible for phosphorylating mannose residues to form mannose-6-phosphate.

What are the main functions of proteoglycans and GAGs in the extracellular matrix?

Providing hydration, resisting compression (due to their negative charge attracting water), lubrication, and acting as molecular sieves.

What distinguishes Hunter syndrome from Hurler syndrome?

Hunter syndrome is X-linked (vs. autosomal recessive), does not typically present with corneal clouding, and is caused by a deficiency in iduronate sulfatase.

What are glycosaminoglycans (GAGs)?

Long, negatively charged, unbranched heteropolysaccharide chains composed of repeating disaccharide units.

What are the acidic sugars found in glycosaminoglycans?

Glucuronic acid and Iduronic acid.

What role does mannose-6-phosphate play in lysosomal targeting?

It targets N-linked glycoproteins to lysosomes for degradation.

What defines mucopolysaccharidoses?

A group of disorders caused by deficiencies in the enzymes that degrade glycosaminoglycans.

What are the clinical features of Hurler syndrome?

Coarse facial features, corneal clouding, skeletal abnormalities, hepatosplenomegaly, and severe intellectual disability.

How are proteoglycans structured?

Proteoglycans are formed by covalent linkage of GAGs to a core protein, with multiple GAG chains attached.

What distinguishes glycoproteins from proteoglycans?

Glycoproteins have shorter, often branched carbohydrate chains, while proteoglycans have long, unbranched chains.

What happens in I-cell disease?

Hydrolytic enzymes are absent from lysosomes, leading to accumulation of substances destined for degradation.

What is the significance of sulfation in GAGs?

Sulfation adds negative charges, contributing to the structural properties and functions of GAGs.

What are the main functions of glycoproteins?

Cell surface receptors, antibodies, plasma proteins, enzymes, and hormones.

What are some major types of glycosaminoglycans (GAGs)?

Hyaluronic acid, chondroitin sulfate, keratan sulfate, dermatan sulfate, and heparin/heparan sulfate.

What is unique about hyaluronic acid among GAGs?

It is the only GAG not covalently linked to a protein (not forming proteoglycans) and is not sulfated.

What is the primary defect in I-cell disease?

A deficiency in N-acetylglucosaminyl-1-phosphotransferase, which is responsible for phosphorylating mannose residues to form mannose-6-phosphate.

What are the main functions of proteoglycans and GAGs in the extracellular matrix?

Providing hydration, resisting compression (due to their negative charge attracting water), lubrication, and acting as molecular sieves.

What distinguishes Hunter syndrome from Hurler syndrome?

Hunter syndrome is X-linked (vs. autosomal recessive), does not typically present with corneal clouding, and is caused by a deficiency in iduronate sulfatase.

What contributes to the strong negative charge of glycosaminoglycans (GAGs)?

The presence of carboxyl groups on acidic sugars and sulfate groups.

What specific enzyme deficiency is found in Hunter syndrome?

Iduronate sulfatase.

In the context of proteoglycans, what specific residue often forms the link between the GAG chain and the core protein?

A xylose residue, typically to a serine hydroxyl group on the core protein.

What is the general consequence of the enzyme defect in I-cell disease on the lysosomal enzymes themselves?

Lysosomal hydrolytic enzymes are secreted into the bloodstream rather than being delivered to lysosomes.

What is the inheritance pattern for Hurler syndrome?

Autosomal recessive.

What is the primary function of the mannose-6-phosphate tag on N-linked glycoproteins?

To serve as a recognition marker for receptors that transport these enzymes to lysosomes.