Chapter 14

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Questions and Answers

What characterizes the carbohydrate chains of glycoproteins?

They are exclusively found in membrane-bound glycoproteins.

They are typically long and linear.

They usually consist of repeating disaccharide units.

They are usually two to ten sugar residues long and may be branched. (correct)

Which statement accurately describes the synthesis of N-linked glycoproteins?

They are synthesized exclusively in the plasma.

They are produced solely from nucleotide sugars.

They involve the transfer of a preformed oligosaccharide to asparagine residues. (correct)

They are synthesized in the rough endoplasmic reticulum without any precursors.

What causes mucopolysaccharidoses?

Defects in the targeting of glycoproteins to the Golgi apparatus.

Deficiencies in the degradation of glycosaminoglycans. (correct)

Increased synthesis of core proteins in proteoglycans.

Elevated levels of lysosomal enzymes in the blood.

The presence of sulfated compounds in urine may indicate a deficiency in which enzyme?

Sulfatase Signup and view all the answers

What is the primary biochemical defect causing I-cell disease?

Deficiency in a protein that synthesizes mannose 6-phosphate. Signup and view all the answers

Hurler syndrome is confirmed by the deficiency of which enzyme?

α-L-Iduronidase Signup and view all the answers

In I-cell disease, what is a notable change in the blood levels of certain substances?

Elevated levels of acid hydrolases. Signup and view all the answers

What distinguishes glycoproteins from proteoglycans?

Glycoproteins have short, branched oligosaccharide chains attached to proteins. Signup and view all the answers

Which condition results from the accumulation of partially degraded structures in lysosomes?

Oligosaccharidosis Signup and view all the answers

What type of sugars primarily compose the repeating unit in glycosaminoglycans (GAGs)?

Acidic sugar and amino sugar Signup and view all the answers

What are large complexes of negatively charged heteropolysaccharides known as?

Glycosaminoglycans Signup and view all the answers

Which of the following is NOT a type of glycosaminoglycan (GAG)?

Lactose Signup and view all the answers

What is the role of glycosaminoglycans (GAGs) in the body?

To bind large amounts of water and form a gel-like matrix Signup and view all the answers

What happens when there is a deficiency of lysosomal acid hydrolases in relation to GAGs?

GAGs are accumulated, leading to mucopolysaccharidosis Signup and view all the answers

Which molecule is involved in the last step of GAG synthesis by providing sulfate?

3′-phosphoadenosyl-5′-phosphosulfate Signup and view all the answers

How are GAGs primarily structured within the body?

Covalently attached to proteins, forming proteoglycans Signup and view all the answers

What is the difference between hyaluronic acid and other GAGs?

Hyaluronic acid is not covalently attached to protein Signup and view all the answers

Which of the following conditions is associated with the accumulation of GAGs in tissues?

Mucopolysaccharidosis Signup and view all the answers

What are the primary amino sugars found in GAGs?

D-glucosamine and D-galactosamine Signup and view all the answers

Where are glycosaminoglycans (GAGs) synthesized in the cell?

Golgi apparatus Signup and view all the answers

Study Notes

Glycosaminoglycans (GAGs)

Composed of long, negatively charged, unbranched heteropolysaccharide chains with repeating disaccharide units: [acidic sugar–amino sugar]n.
Amino sugars can be D-glucosamine or D-galactosamine, typically acetylated to eliminate a positive charge.
Acidic sugars include D-glucuronic acid and its epimer L-iduronic acid.
Crucial for retaining water, contributing to a gel-like matrix in the body's ground substance.
GAGs are known for their viscous properties, leading to the historical term "mucopolysaccharides."
Major types include chondroitin 4- and 6-sulfates, keratan sulfate, dermatan sulfate, heparin, heparan sulfate, and hyaluronic acid.
All GAGs, except hyaluronic acid, are covalently linked to proteins, forming proteoglycan monomers with a core protein.
Synthesized in the Golgi through the addition of alternating acidic and amino sugars donated by UDP derivatives.
Characterized by possible sulfation of amino sugars derived from 3′-phosphoadenosyl-5′-phosphosulfate.
Degraded by lysosomal acid hydrolases; a deficiency leads to mucopolysaccharidoses, causing skeletal deformities and intellectual disability.
Common examples of mucopolysaccharidoses include Hunter and Hurler syndromes.

Glycoproteins

Proteins that have short, branched oligosaccharide chains (2-10 sugar residues).
Distinct from proteoglycans as they do not have long serial disaccharide units.
Play roles in cell-surface recognition, antigenicity, and comprise extracellular matrix components.
Major components of human plasma globular proteins are glycoproteins.
Synthesized in the rough endoplasmic reticulum (RER) and Golgi from nucleotide sugars.
O-linked glycoproteins formed by transferring sugars to serine or threonine residues; N-linked glycoproteins synthesized via transfer from dolichol pyrophosphate to asparagine residues.
I-cell disease results from a deficiency in the phosphorylation of mannose residues in N-linked glycoprotein enzymes.

Lysosomal Storage Diseases

Mucopolysaccharidosis caused by defects in GAG degradation rather than protein synthesis.
Blood enzyme levels remain normal in storage diseases; the enzyme targeted to lysosomes is nonfunctional.
I-cell disease showcases elevated blood acid hydrolases due to enzyme secretion failure, with subsequent lysosomal accumulation.

Diagnostic Questions and Answers

Mucopolysaccharidoses are caused by deficiencies in lysosomal acid hydrolases responsible for GAG degradation.
Urinary analysis showing sulfated compounds indicates deficiencies in sulfatase, essential for the degradation process.
I-cell disease confirmed by elevated acid hydrolases in blood due to defective mannose 6-phosphate targeting.
Hurler syndrome, indicated by corneal clouding and specific GAGs in urine, results from α-L-iduronidase deficiency.

Comparison: Glycoproteins vs. Proteoglycans

Glycoproteins: Short, branched carbohydrate chains; diverse functions in cell recognition and signaling.
Proteoglycans: Long GAG chains attached to core proteins; essential for structural components of extracellular matrices and create gel-like properties.

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Description

This quiz provides an overview of glycosaminoglycans (GAGs), their structure, and components, including the essential disaccharide units formed by amino and acidic sugars. Test your knowledge on the characteristics and modifications of GAGs, such as sulfation and acetylation. Understand the role these molecules play in biological processes.