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Questions and Answers
What is the primary defect causing the symptoms in the case of the 5-year-old boy?
What is the primary defect causing the symptoms in the case of the 5-year-old boy?
Which factor contributes significantly to the formation of keloids in individuals?
Which factor contributes significantly to the formation of keloids in individuals?
What skin characteristic is commonly associated with Ehlers-Danlos syndrome?
What skin characteristic is commonly associated with Ehlers-Danlos syndrome?
Which of the following is NOT a symptom typically associated with Ehlers-Danlos syndrome?
Which of the following is NOT a symptom typically associated with Ehlers-Danlos syndrome?
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How is hearing loss in individuals with Ehlers-Danlos syndrome typically manifested?
How is hearing loss in individuals with Ehlers-Danlos syndrome typically manifested?
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Which collagen type is primarily found in bones, dentin, tendons, and dermis?
Which collagen type is primarily found in bones, dentin, tendons, and dermis?
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What structural feature distinguishes collagen fibers as observed under electron microscopy?
What structural feature distinguishes collagen fibers as observed under electron microscopy?
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Which disorder is characterized by a lack of vitamin C affecting collagen synthesis?
Which disorder is characterized by a lack of vitamin C affecting collagen synthesis?
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What describes the primary defect in Ehlers-Danlos type VII?
What describes the primary defect in Ehlers-Danlos type VII?
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What is the primary composition of each tropocollagen molecule?
What is the primary composition of each tropocollagen molecule?
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Which amino acid is present at every third position in the α-chain of tropocollagen?
Which amino acid is present at every third position in the α-chain of tropocollagen?
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What symptom is primarily associated with Ehlers-Danlos type VI?
What symptom is primarily associated with Ehlers-Danlos type VI?
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What is a common symptom of osteogenesis imperfecta?
What is a common symptom of osteogenesis imperfecta?
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Which cell type is primarily responsible for synthesizing collagen type I?
Which cell type is primarily responsible for synthesizing collagen type I?
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What is the role of vitamin C in collagen synthesis?
What is the role of vitamin C in collagen synthesis?
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Which amino acid is NOT characteristic of collagen?
Which amino acid is NOT characteristic of collagen?
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What process occurs immediately after the formation of procollagen in collagen synthesis?
What process occurs immediately after the formation of procollagen in collagen synthesis?
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Which type of collagen is specifically formed by chondroblasts?
Which type of collagen is specifically formed by chondroblasts?
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What is the final form of collagen after the cleavage of procollagen?
What is the final form of collagen after the cleavage of procollagen?
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Which of the following is a step in the synthesis of collagen that requires amino acid modification?
Which of the following is a step in the synthesis of collagen that requires amino acid modification?
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Which of the following correctly describes the grouping of collagen chains during biosynthesis?
Which of the following correctly describes the grouping of collagen chains during biosynthesis?
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Study Notes
Collagen Synthesis
- Collagen is the most abundant protein in the body.
- It is a protein made up of amino acids like glycine, proline, and hydroxyproline.
- It is secreted mainly by fibroblasts.
- There are about 46 types of collagen.
- Collagen is essential for the structure of hair, skin, nails, bones, ligaments, and tendons.
- Different cells produce different types of collagen, including:
- Fibroblasts, chondroblasts, osteoblasts, and odontoblasts produce collagen type I.
- Chondroblasts also produce collagen type II.
- Smooth muscle, reticular cells, Schwann cells, and hepatocytes produce collagen type III.
- Endothelial, epithelial cells, muscle cells, and Schwann cells produce collagen type IV.
Collagen Biosynthesis
- Collagen biosynthesis involves several steps within and outside the cell:
- Inside the cell: mRNA is synthesized from a DNA template in the fibroblast nucleus. mRNA travels to the rough endoplasmic reticulum (RER) and attaches to ribosomes where translation occurs.
- Preprocollagen is produced and released into the RER lumen.
- Pro-alpha chains are formed through modification of preprocollagen.
- Hydroxylation: Proline and lysine within the polypeptide chains are hydroxylated, requiring vitamin C as a cofactor.
- Glycosylation: Hydroxylysine residues are glycosylated (addition of sugar).
- Procollagen formation: Three polypeptide chains assemble into a triple helix.
- Golgi transport and secretion: Procollagen is transported to the Golgi apparatus, packaged, and secreted by exocytosis.
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Outside the cell:
- Cleavage: Procollagen peptidases remove registration peptides, transforming soluble procollagen into insoluble tropocollagen (collagen molecule).
- Assembly: Tropocollagen aggregates to form collagen fibrils.
- Depending on the type, these fibrils may form fibers or bundles.
Collagen Structure
- Collagen fibers display cross-banding at regular intervals of 67 nm under electron microscopy.
- These fibers are formed from parallel aggregates of thinner fibrils.
- Tropocollagen molecules are the basic subunits of fibrils, and they are roughly 300 nm long and 1.5 nm in diameter.
- Each tropocollagen molecule comprises three polypeptide chains (α-chains) wrapped around each other in a triple helical configuration.
- Each α-chain is composed of about 1000 amino acid residues.
- Every third amino acid in the chain is glycine, and proline, hydroxyproline, and hydroxylysine make up the remaining amino acids.
Collagen Defects and Clinical Disorders
- Defects in collagen synthesis can lead to a range of clinical disorders.
- Below are some examples:
- Ehlers-Danlos Syndrome (EDS) Type IV: Results from faulty transcription or translation of collagen type III, leading to aortic and/or intestinal rupture.
- EDS Type VI: Occurs due to faulty lysine hydroxylation, causing increased skin elasticity and potential eyeball rupture.
- EDS Type VII: A decrease in procollagen peptidase activity results in increased articular mobility and frequent luxations.
- Scurvy: A deficiency in vitamin C (a cofactor for prolyl hydroxylase) disrupts collagen synthesis, leading to ulceration of the gums and hemorrhages.
- Osteogenesis Imperfecta (OI) (Brittle Bone Disease): A change in one nucleotide in genes responsible for collagen type I causes spontaneous fractures, bone deformities, and potential cardiac insufficiency.
Clinical Scenario:
- A 5-year-old boy presents with excessive bruising and hypermobile joints.
- This suggests a likely defect in α-collagen triple helix formation, which is vital for the structural integrity of collagen fibers.
Medical Application
- Keloids: These are abnormal scars consisting mainly of type III collagen initially, which is eventually replaced by type I collagen.
- Keloids form due to an overgrowth of granulation tissue at the site of healed skin injury.
- They are more common in individuals of African descent and are challenging to manage due to their tendency to recur.
Additional Information
- α1-antitrypsin is an enzyme inhibitor that is not directly involved in collagen synthesis.
- Fibrillin-1 glycoprotein is a component of elastic fibers, not collagen.
- Proline and lysine hydroxylation is a critical step in collagen synthesis, so defects in this process would affect collagen structure and likely contribute to the patient's symptoms.
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Description
This quiz explores the vital role of collagen in the body, detailing its composition, types, and the cells responsible for its production. It also delves into the process of collagen biosynthesis, emphasizing the steps involved within and outside the cell. Test your knowledge on this crucial protein and its synthesis mechanisms.
