Glycosaminoglycans and Their Classification

Questions and Answers

What characteristic of glycosaminoglycans (GAGs) contributes to the resiliency of synovial fluid?

Compressive elasticity

Repulsion of their negative charges (correct)

Absence of sulfate units

Presence of amino sugars

What is the primary structural component of keratan sulfate?

D-glucuronate linked to N-acetylglucosamine

Chondroitin sulfate derivatives

Fucose attached via α (1→4) linkages

Galactose rather than acidic sugar (correct)

Which glycosaminoglycan serves as an anticoagulant?

Dermatan sulfate

Heparin (correct)

Chondroitin sulfate

Hyaluronic acid

What defines the polyanionic nature of hyaluronic acid?

Linkage of D-glucuronate to N-acetylglucosamine Signup and view all the answers

How are glycosaminoglycans primarily classified?

Monomeric compositions and type of linkages Signup and view all the answers

What effect does compressing a solution of GAGs have?

Squeezes out water Signup and view all the answers

Which characteristic is NOT associated with hyaluronic acid?

Has a high degree of sulfation Signup and view all the answers

Where is heparin primarily found?

Within mast cells Signup and view all the answers

What role do the negative charges on GAGs play in biological systems?

Contribute to fluid dynamics Signup and view all the answers

Which of the following is NOT a type of sulfated disaccharide unit GAG?

Hyaluronic acid Signup and view all the answers

What process is involved in the elongation of polysaccharide chains of GAGs?

Glycosylation Signup and view all the answers

Where does the synthesis of GAGs primarily occur?

Golgi apparatus Signup and view all the answers

Which enzymes are responsible for catalyzing the reactions involved in GAG synthesis?

Glycosyltransferases Signup and view all the answers

What types of sugars are alternately added to elongate GAG chains?

Acidic and amino sugars Signup and view all the answers

Which of the following GAGs is primarily known for its presence in cartilage?

Chondroitin sulfate Signup and view all the answers

What is the main structural feature of GAGs?

Sulfated disaccharide units Signup and view all the answers

Which cellular organelle is directly involved in the synthesis of GAGs alongside the Golgi apparatus?

Smooth endoplasmic reticulum Signup and view all the answers

What role do UDP-derivatives play in the synthesis of GAGs?

They donate sugars for polymerization. Signup and view all the answers

What is a common misconception about GAGs?

GAGs do not contribute to cellular functions. Signup and view all the answers

What type of bond is formed between xylose and serine residue?

O-glycosidic bond Signup and view all the answers

Which of the following describes the bonding in bacterial cell walls as it relates to N-acetylmuramic acid?

β (1→4)-linked residues forming a mesh-like structure Signup and view all the answers

What is the function of lysozyme in relation to peptidoglycan?

Cleaves the glycosidic bond between certain sugars Signup and view all the answers

How does penicillin exert its antibiotic action?

By inhibiting the formation of cross-links in peptidoglycan Signup and view all the answers

Glycoprotein storage diseases are primarily caused by what mechanism?

Deficiency of a degradative enzyme Signup and view all the answers

Which characteristic describes the action of lysosomal hydrolytic enzymes on glycoproteins?

They act in sequence, reverse to incorporation Signup and view all the answers

What is the primary amino acid involved in the attachment of sugars in N-linked glycoproteins?

Asparagine Signup and view all the answers

Which of the following is NOT one of the three major classes of N-linked glycoproteins?

Low mannose Signup and view all the answers

In which cellular organelle are N-linked glycoproteins primarily modified and processed?

Golgi apparatus Signup and view all the answers

What does the carbohydrate portion of N-linked glycoproteins primarily determine?

Biological function and cell recognition Signup and view all the answers

How are glycoproteins that are to be secreted from the cell processed in the Golgi?

They remain in the lumen and bud off into vesicles. Signup and view all the answers

What kind of glycoprotein may likely have a more complex carbohydrate structure?

Complex Signup and view all the answers

During the vesicle transport process, where does the carbohydrate portion of glycoproteins end up?

On the outside of the cell membrane Signup and view all the answers

What feature is characteristic of High mannose glycoproteins?

They have a high ratio of mannose sugars. Signup and view all the answers

What is the fate of membrane-bound proteins that bud off into vesicles from the Golgi?

They release into the extracellular space. Signup and view all the answers

What type of linkage connects the sugar to the asparagine residue in N-linked glycoproteins?

Amide bond Signup and view all the answers

Where are most proteins synthesized?

On free ribosomes in the cytosol Signup and view all the answers

What is a function of signal sequences in proteins?

To direct proteins to their proper destinations Signup and view all the answers

Which of the following proteins are synthesized on ribosomes attached to the rough endoplasmic reticulum?

Proteins destined for cellular membranes Signup and view all the answers

How are glycoproteins transported after synthesis?

Via secretory vesicles to the Golgi complex Signup and view all the answers

What type of proteins are synthesized in the cytosol?

Most proteins that function in the cytoplasm Signup and view all the answers

What happens to a growing polypeptide that contains a signal sequence?

It is extruded into the lumen of the rough endoplasmic reticulum Signup and view all the answers

Which organelle is primarily responsible for processing glycoproteins after they are synthesized?

Golgi complex Signup and view all the answers

What type of proteins typically have their synthesis associated with rough endoplasmic reticulum?

Exported proteins and membrane proteins Signup and view all the answers

Which of the following is NOT a destination for proteins synthesized on the rough endoplasmic reticulum?

Cytoplasmic ribosomes Signup and view all the answers

What is the primary role of glycoproteins in cellular function?

To be components of the cell membrane and signaling Signup and view all the answers

Study Notes

Types of Glycosaminoglycans (GAGs)

GAGs are characterized by their slippery consistency, contributing to mucous secretions and synovial fluid.
Keratan sulfate contains galactose instead of the typical acidic sugar.
Heparin acts as a free glycosaminoglycan, serving as an anticoagulant and is found intracellularly in mast cells and near blood vessels.
Hyaluronic acid is a polyanionic GAG composed of alternating D-glucuronate and N-acetylglucosamine, forming viscoelastic solutions that function as biological shock absorbers and lubricants.

Classification of Glycosaminoglycans

Major classes are classified based on monomeric composition, glycosidic linkages, sulfate unit arrangement, and location.
Other GAG types include chondroitin sulfate, dermatan sulfate, and keratan sulfate, which consist of sulfated disaccharide units.

Synthesis of Glycosaminoglycans

Polysaccharide chains form by sequential addition of acidic and amino sugars from UDP derivatives, catalyzed by glycosyltransferases.
Synthesis occurs primarily in the endoplasmic reticulum and Golgi apparatus.

Synthesis of Glycoproteins

Most proteins are synthesized on free ribosomes in the cytosol for cytoplasmic function.
Proteins targeting membranes, lysosomes, or export are synthesized on ribosomes attached to the rough endoplasmic reticulum (RER) with signal sequences directing protein localization.
Glycoprotein synthesis involves extrusion into the RER lumen, followed by transport to the Golgi complex.

N-Linked Glycoproteins

Sugars attach to the NH2 group of asparagine residues via an amide bond.
Major N-linked glycoprotein classes include high mannose, hybrid, and complex types.
Glycoproteins integrating into the cell membrane have carbohydrate portions oriented outward.

Carbohydrate Components of Glycoproteins

O-glycosidic bonds can form between serine and xylose via serine hydroxyl groups, contributing to glycoprotein structure.

Bacterial Cell Walls

Bacterial polysaccharides consist mainly of β(1→4)-linked N-acetylmuramic acid and N-acetylglucosamine.
N-acetylmuramic acid is linked via amide bonds to tetrapeptides, creating a durable meshlike structure.

Enzymatic Actions

Lysozyme: Cleaves glycosidic bonds in peptidoglycan, facilitating degradation.
Penicillin: Inhibits cross-link formation in peptidoglycan, exerting antibiotic effects.

Lysosomal Glycoprotein Degradation

Lysosomal hydrolytic enzymes are specific for sequentially removing glycoprotein components, mainly as exoenzymes.
Deficiency in any degradative enzyme leads to glycoprotein storage diseases (oligosaccharidoses), causing partially degraded structures to accumulate in lysosomes and potentially result in cell death.
These conditions often correlate with deficiencies that affect mucopolysaccharidoses and glycocalipid degradation.

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Description

Explore the fascinating world of glycosaminoglycans (GAGs) with this quiz. Learn about their types, functions, and synthesis, including specific details of keratan sulfate, heparin, and hyaluronic acid. Test your knowledge on their classification and roles in biological systems.