Collagen and Elastin — MCQs
A 60 year old lady is concerned about the wrinkles around her eyes. This is primarily due to alterations in
Which type of collagen is primarily responsible for forming the basement membrane sheets?
A 10-year-old boy presents with frequent fractures and blue sclerae. This patient most likely carries a mutation in a gene that encodes which of the following proteins?
Osteogenesis imperfecta is due to a defect in what?
Blue sclera is seen in all of the following conditions except:
In Marfan syndrome, the defect is in the gene encoding which protein?
Which of the following is not typically associated with osteogenesis imperfecta?
An adult tall male presents with a long arm span, pectus excavatum, and cardiac abnormalities. What is the most likely defective protein?
Most abundant collagen in the body is
Which of the following protein molecules is responsible for cell-to-cell adhesion?
Collagen and Elastin Indian Medical PG Practice Questions and MCQs
Question 1: A 60 year old lady is concerned about the wrinkles around her eyes. This is primarily due to alterations in
- A. Fibrillin
- B. Collagen cross linking (Correct Answer)
- C. Collagenase
- D. Desmosine
Explanation: ***Collagen cross linking*** - With aging, the **collagen fibers** in the skin undergo structural changes, including a decrease in efficient cross-linking. - This reduction in **collagen cross-linking** leads to a loss of skin elasticity and tensile strength, contributing to the formation of wrinkles. *Fibrillin* - **Fibrillin** is a glycoprotein that is essential for the formation of elastic fibers, not primarily collagen. - Defects in fibrillin are associated with conditions like **Marfan syndrome**, which affects connective tissue integrity but is not the primary cause of age-related wrinkles. *Collagenase* - **Collagenase** is an enzyme that breaks down collagen; an increase in its activity can contribute to collagen degradation. - While collagenase activity plays a role in skin aging, the *deficiency* or *defect* is not the primary cause of wrinkles, rather it is the overall degradation and altered structure of collagen. *Desmosine* - **Desmosine** is a unique amino acid that is part of **elastin fibers**, not collagen. - It is crucial for the elasticity of tissues but a defect in desmosine itself is not the direct cause of age-related wrinkles, which are more directly related to collagen structure.
Question 2: Which type of collagen is primarily responsible for forming the basement membrane sheets?
- A. Type I
- B. Type II
- C. Type IV (Correct Answer)
- D. Type VI
Explanation: ***Type IV*** - **Type IV collagen** is unique as it forms a **two-dimensional network** that constitutes the structural foundation of **basement membranes**. - Its structure, with **non-fibrillar domains**, allows for assembly into sheets rather than fibrils, providing essential support and filtration properties. *Type I* - **Type I collagen** is the most abundant type in the human body, providing **tensile strength** to tissues like **skin, bone, tendons**, and ligaments. - It forms **thick, striated fibrils** and does not primarily associate with basement membranes [1]. *Type II* - **Type II collagen** is the main collagen found in **cartilage**, providing **resilience and shock absorption**. - It forms thin fibrils within the cartilage matrix and is not a component of basement membranes. *Type VI* - **Type VI collagen** is a minor fibrillar collagen that associates with **interstitial connective tissues**, often forming a **microfibrillar network**. - It links cells to the surrounding matrix and is not a primary component of basement membrane sheets.
Question 3: A 10-year-old boy presents with frequent fractures and blue sclerae. This patient most likely carries a mutation in a gene that encodes which of the following proteins?
- A. Collagen (Correct Answer)
- B. Fibrillin
- C. Keratin
- D. Myosin
Explanation: ***Collagen*** - Collagen mutations commonly result in various **connective tissue disorders** and defects in structural integrity [1]. - It plays a critical role in **skin, bones, and cartilage**, making it a significant candidate for mutations affecting these areas [1]. *Keratin* - Keratin is a protein primarily found in **skin, hair, and nails**, and mutations typically cause **epidermal dysplasia or disorders** like keratoderma. - While important for structural integrity, keratin is less associated with broader connective tissue disorders. *Fibrillin* - Fibrillin is essential for maintaining the **elasticity and structure of connective tissues**, predominantly in **Marfan syndrome** [2]. - Mutations lead to issues with connective tissue but are not as broadly relevant as collagen in this context [2]. *Myosin* - Myosin is primarily involved in **muscle contraction** and is not typically associated with **connective tissue** disorders. - Mutations in myosin often relate to **muscle diseases**, which are not relevant to the context of connective tissue mutations. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 154-155. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 153-154.
Question 4: Osteogenesis imperfecta is due to a defect in what?
- A. Type II collagen
- B. Type IV collagen
- C. Type I collagen (Correct Answer)
- D. Type III collagen
Explanation: ***Collagen 1*** - Osteogenesis imperfecta is primarily caused by a defect in **type I collagen** [2], which is crucial for bone strength and structure. - This defect leads to **brittle bones**, resulting in frequent fractures and skeletal deformities . *Collagen 2* - Type II collagen is mainly found in **cartilage** and is critical for **hyaline cartilage formation**, not directly involved in bone integrity. - Defects in type II collagen are associated with conditions like **chondrodysplasia**, rather than osteogenesis imperfecta. *Collagen 4* - Type IV collagen is primarily found in **basement membranes** and plays a role in filtration and structural integrity of tissues. - While important for kidney and eye function, it is not related to the bone fragility seen in osteogenesis imperfecta. *Collagen 3* - Type III collagen is involved in the structure of **reticular fibers** and is crucial for skin and blood vessel integrity. - It is not the primary collagen affected in osteogenesis imperfecta, which is associated specifically with type I collagen defects. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, p. 1182. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, p. 1188.
Question 5: Blue sclera is seen in all of the following conditions except:
- A. Marfan's syndrome
- B. Osteogenesis imperfecta
- C. Keratoconus (Correct Answer)
- D. Rheumatoid arthritis
Explanation: ***Keratoconus*** - Keratoconus is a progressive eye disease in which the normally round cornea thins and begins to bulge into a cone-like shape, leading to **vision distortion**. - Blue sclera is **not a feature** of keratoconus. This is a **corneal condition** that does not affect the sclera. - Blue sclera, seen in the other conditions listed, occurs due to thinning of the sclera, making the underlying choroidal pigment visible. *Marfan's syndrome* - Patients with Marfan's syndrome can have blue sclera due to the **thinning of collagen** in the scleral tissue, allowing the underlying choroid to show through. - This connective tissue disorder affects multiple body systems, including the skeletal, cardiovascular, and ocular systems, with features like **arachnodactyly** and **aortic root dilation**. *Osteogenesis imperfecta* - Often referred to as **brittle bone disease**, osteogenesis imperfecta is characterized by defective **type I collagen synthesis**, which also affects the sclera. - The sclera becomes thin and translucent, revealing the underlying choroidal pigment, thus appearing **blue**. *Rheumatoid arthritis* - In rheumatoid arthritis, particularly with severe or long-standing disease, the sclera can become thinned due to **scleritis** or **scleromalacia perforans**. - This thinning can lead to a **blue discoloration** of the sclera, making the underlying choroid visible.
Question 6: In Marfan syndrome, the defect is in the gene encoding which protein?
- A. Fibrillin I (Correct Answer)
- B. Fibrillin II
- C. Elastin
- D. Collagen
Explanation: ***Fibrillin I*** - Marfan syndrome arises from a defect in **fibrillin I**, which is essential for the proper formation of elastic fibers in connective tissue [1]. - This defect leads to symptoms affecting the **musculoskeletal**, **cardiovascular**, and **ocular systems** due to weakened connective tissue structure [1]. *Collagen* - While collagen is an important structural protein, it is not the primary defect in Marfan syndrome. - Disorders affecting collagen include **Ehlers-Danlos syndrome**, which presents with different clinical features such as hypermobility. *Fibrillin II* - Fibrillin II is related to different connective tissue conditions but is not involved in Marfan syndrome. - Its mutations are associated with **other disorders**, not the hallmark manifestations seen in Marfan. *Elastin* - Elastin provides elasticity in vascular and other tissues; however, it is not directly related to Marfan syndrome. - Conditions such as **Williams syndrome** involve elastin, but they present distinct clinical features from Marfan syndrome. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. With Illustrations By, pp. 35-36.
Question 7: Which of the following is not typically associated with osteogenesis imperfecta?
- A. Blue sclera
- B. Lax ligament
- C. Bilateral Hip dislocation (Correct Answer)
- D. Osteoporosis
Explanation: ***Bilateral Hip dislocation*** - While hip dislocations can occur in severe cases due to bone fragility, **bilateral hip dislocation** is not a characteristic or typical primary association with osteogenesis imperfecta. - The underlying issue is primarily **bone fragility** leading to fractures, not inherent joint instability or malformation causing bilateral dislocation. *Blue sclera* - **Blue sclera** is a classic sign of osteogenesis imperfecta, caused by the thinness of the sclera allowing the underlying choroid vessels to show through. - This is due to a defect in **Type I collagen** synthesis, which affects not only bones but also other connective tissues including the sclera. *Lax ligament* - **Lax ligaments** are common in osteogenesis imperfecta due to the generalized **connective tissue defect**, particularly involving Type I collagen. - This can contribute to joint instability, *hypermobility*, and an increased risk of sprains. *Osteoporosis* - **Osteoporosis** with reduced bone mineral density is a hallmark feature of osteogenesis imperfecta, leading to **fragile bones** and recurrent fractures. - The genetic defect in **Type I collagen** impairs bone matrix formation, resulting in weak and brittle bones.
Question 8: An adult tall male presents with a long arm span, pectus excavatum, and cardiac abnormalities. What is the most likely defective protein?
- A. Fibrillin (Correct Answer)
- B. Elastin
- C. Collagen
- D. Myosin
- E. Laminin
Explanation: ***Fibrillin*** - The constellation of **tall stature**, **long arm span**, **pectus excavatum**, and **cardiac abnormalities** (e.g., aortic dissection or mitral valve prolapse) is classic for **Marfan syndrome**. - Marfan syndrome is caused by a defect in the *FBN1* gene, which codes for **fibrillin-1**, a glycoprotein essential for the formation of elastic fibers in connective tissue. *Elastin* - Defects in **elastin** are associated with conditions like **supravalvular aortic stenosis** (due to **Williams syndrome**) or cutis laxa, which have different phenotypic presentations. - While both elastin and fibrillin are components of elastic fibers, the specific features of Marfan syndrome point to fibrillin as the primary defect. *Collagen* - Defects in **collagen** (especially type I, III, or V) are associated with conditions such as **osteogenesis imperfecta** (brittle bones) or **Ehlers-Danlos syndrome** (hypermobility, skin hyperextensibility). - These conditions typically present with different clinical manifestations, lacking the specific combination of features seen in this patient. *Myosin* - **Myosin** is a fibrous protein primarily involved in **muscle contraction** and is not directly implicated in widespread connective tissue disorders affecting skeletal and cardiovascular systems in this manner. - Defects in myosin are more commonly associated with various forms of **cardiomyopathy** or skeletal muscle myopathies, not Marfan-like features. *Laminin* - **Laminin** is a major component of the **basement membrane** and plays a role in cell adhesion, migration, and tissue architecture. - Laminin defects are associated with certain forms of **muscular dystrophy** (e.g., congenital muscular dystrophy) and **epidermolysis bullosa**, not the specific skeletal and cardiovascular features of Marfan syndrome.
Question 9: Most abundant collagen in the body is
- A. Type I (Correct Answer)
- B. Type II
- C. Type V
- D. Type VI
Explanation: ***Type I*** - **Type I collagen** is the most abundant type in the human body, constituting about 90% of the body's total collagen. - It is primarily found in **skin, tendons, ligaments, bone, dentin, and intervertebral discs**, providing mechanical strength and structural integrity. *Type II* - **Type II collagen** is the main collagen found in **cartilage**, especially hyaline and elastic cartilage. - It provides resistance to pressure and is crucial for the structure of the **intervertebral disc nucleus pulposus** and the **vitreous humor of the eye**. *Type V* - **Type V collagen** is a minor fibrillar collagen that associates with **type I collagen** to regulate fibril diameter and organization. - It is found in **cornea, bone, and interstitial matrices**, playing a role in tissue development and integrity. *Type VI* - **Type VI collagen** is a microfibrillar collagen that forms bead-like microfibrils and is found in most **interstitial tissues**. - It plays a significant role in anchoring other extracellular matrix components and is particularly abundant in the **basement membranes** of blood vessels and muscles.
Question 10: Which of the following protein molecules is responsible for cell-to-cell adhesion?
- A. Laminin
- B. Fibronectin
- C. Collagen
- D. Cadherin (Correct Answer)
Explanation: ***Cadherin*** - **Cadherins** are transmembrane proteins that mediate **direct cell-to-cell adhesion** in a calcium-dependent manner - They form **adherens junctions** and **desmosomes**, which are essential for maintaining tissue integrity - Cadherins on adjacent cells bind to each other (**homophilic binding**), creating strong cell-cell connections - Critical for **embryonic development**, tissue architecture, and **epithelial barrier function** *Fibronectin* - **Fibronectin** is an extracellular matrix glycoprotein that mediates **cell-to-ECM adhesion**, not direct cell-to-cell adhesion - It binds to **integrins** on the cell surface, facilitating cell attachment to the extracellular matrix - Important for cell migration, wound healing, and embryonic development - Does not directly connect cells to each other *Collagen* - **Collagen** is the most abundant structural protein providing **tensile strength** to connective tissues - Primarily functions as **extracellular scaffolding**, not as an adhesion molecule - Provides mechanical support but does not mediate cell-cell adhesion *Laminin* - **Laminins** are major components of the **basal lamina** (basement membrane) - Mediate **cell-to-basal lamina adhesion** through integrin receptors - Important for cell differentiation, migration, and tissue organization - Function in cell-to-ECM adhesion, not cell-to-cell adhesion
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