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Questions and Answers
What characteristic of glycosaminoglycans (GAGs) contributes to the resiliency of synovial fluid?
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?
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?
Which glycosaminoglycan serves as an anticoagulant?
- Dermatan sulfate
- Heparin (correct)
- Chondroitin sulfate
- Hyaluronic acid
What defines the polyanionic nature of hyaluronic acid?
What defines the polyanionic nature of hyaluronic acid?
How are glycosaminoglycans primarily classified?
How are glycosaminoglycans primarily classified?
What effect does compressing a solution of GAGs have?
What effect does compressing a solution of GAGs have?
Which characteristic is NOT associated with hyaluronic acid?
Which characteristic is NOT associated with hyaluronic acid?
Where is heparin primarily found?
Where is heparin primarily found?
What role do the negative charges on GAGs play in biological systems?
What role do the negative charges on GAGs play in biological systems?
Which of the following is NOT a type of sulfated disaccharide unit GAG?
Which of the following is NOT a type of sulfated disaccharide unit GAG?
What process is involved in the elongation of polysaccharide chains of GAGs?
What process is involved in the elongation of polysaccharide chains of GAGs?
Where does the synthesis of GAGs primarily occur?
Where does the synthesis of GAGs primarily occur?
Which enzymes are responsible for catalyzing the reactions involved in GAG synthesis?
Which enzymes are responsible for catalyzing the reactions involved in GAG synthesis?
What types of sugars are alternately added to elongate GAG chains?
What types of sugars are alternately added to elongate GAG chains?
Which of the following GAGs is primarily known for its presence in cartilage?
Which of the following GAGs is primarily known for its presence in cartilage?
What is the main structural feature of GAGs?
What is the main structural feature of GAGs?
Which cellular organelle is directly involved in the synthesis of GAGs alongside the Golgi apparatus?
Which cellular organelle is directly involved in the synthesis of GAGs alongside the Golgi apparatus?
What role do UDP-derivatives play in the synthesis of GAGs?
What role do UDP-derivatives play in the synthesis of GAGs?
What is a common misconception about GAGs?
What is a common misconception about GAGs?
What type of bond is formed between xylose and serine residue?
What type of bond is formed between xylose and serine residue?
Which of the following describes the bonding in bacterial cell walls as it relates to N-acetylmuramic acid?
Which of the following describes the bonding in bacterial cell walls as it relates to N-acetylmuramic acid?
What is the function of lysozyme in relation to peptidoglycan?
What is the function of lysozyme in relation to peptidoglycan?
How does penicillin exert its antibiotic action?
How does penicillin exert its antibiotic action?
Glycoprotein storage diseases are primarily caused by what mechanism?
Glycoprotein storage diseases are primarily caused by what mechanism?
Which characteristic describes the action of lysosomal hydrolytic enzymes on glycoproteins?
Which characteristic describes the action of lysosomal hydrolytic enzymes on glycoproteins?
What is the primary amino acid involved in the attachment of sugars in N-linked glycoproteins?
What is the primary amino acid involved in the attachment of sugars in N-linked glycoproteins?
Which of the following is NOT one of the three major classes of N-linked glycoproteins?
Which of the following is NOT one of the three major classes of N-linked glycoproteins?
In which cellular organelle are N-linked glycoproteins primarily modified and processed?
In which cellular organelle are N-linked glycoproteins primarily modified and processed?
What does the carbohydrate portion of N-linked glycoproteins primarily determine?
What does the carbohydrate portion of N-linked glycoproteins primarily determine?
How are glycoproteins that are to be secreted from the cell processed in the Golgi?
How are glycoproteins that are to be secreted from the cell processed in the Golgi?
What kind of glycoprotein may likely have a more complex carbohydrate structure?
What kind of glycoprotein may likely have a more complex carbohydrate structure?
During the vesicle transport process, where does the carbohydrate portion of glycoproteins end up?
During the vesicle transport process, where does the carbohydrate portion of glycoproteins end up?
What feature is characteristic of High mannose glycoproteins?
What feature is characteristic of High mannose glycoproteins?
What is the fate of membrane-bound proteins that bud off into vesicles from the Golgi?
What is the fate of membrane-bound proteins that bud off into vesicles from the Golgi?
What type of linkage connects the sugar to the asparagine residue in N-linked glycoproteins?
What type of linkage connects the sugar to the asparagine residue in N-linked glycoproteins?
Where are most proteins synthesized?
Where are most proteins synthesized?
What is a function of signal sequences in proteins?
What is a function of signal sequences in proteins?
Which of the following proteins are synthesized on ribosomes attached to the rough endoplasmic reticulum?
Which of the following proteins are synthesized on ribosomes attached to the rough endoplasmic reticulum?
How are glycoproteins transported after synthesis?
How are glycoproteins transported after synthesis?
What type of proteins are synthesized in the cytosol?
What type of proteins are synthesized in the cytosol?
What happens to a growing polypeptide that contains a signal sequence?
What happens to a growing polypeptide that contains a signal sequence?
Which organelle is primarily responsible for processing glycoproteins after they are synthesized?
Which organelle is primarily responsible for processing glycoproteins after they are synthesized?
What type of proteins typically have their synthesis associated with rough endoplasmic reticulum?
What type of proteins typically have their synthesis associated with rough endoplasmic reticulum?
Which of the following is NOT a destination for proteins synthesized on the rough endoplasmic reticulum?
Which of the following is NOT a destination for proteins synthesized on the rough endoplasmic reticulum?
What is the primary role of glycoproteins in cellular function?
What is the primary role of glycoproteins in cellular function?
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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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