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📝 Intermediate filaments structure and function (11 MCQs)

📖 From Principles of Biochemistry • 1. The Foundations of Biochemistry • 11 questions available

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What is Intermediate filaments structure and function?

Definition:
Intermediate filaments are fibrous, rope-like protein polymers with a diameter of about 10 nm, composed of various tissue-specific proteins such as keratins (epithelial cells), vimentins (mesenchymal cells), neurofilaments (neurons), and lamins (nuclear envelope), and they provide mechanical strength and integrity to cells and tissues by resisting tension and linking cell-cell junctions, acting as structural scaffolds that maintain tissue architecture.

Working:
Intermediate filaments work by assembling from coiled-coil dimers that form tetramers, which then associate into protofilaments and finally into 10-nm filaments through a lateral and longitudinal assembly process, and they do not have polarity like actin and microtubules, making them less dynamic, and they connect to desmosomes and hemidesmosomes to transmit mechanical stress across tissues, with their mechanical properties described by the elastic modulus $E = \frac{\sigma}{\varepsilon}$ , where $\sigma$ is stress and $\varepsilon$ is strain.

Example:
A simple example is keratin filaments in skin epithelial cells, which provide strength and protection against mechanical abrasion, and mutations in keratin genes cause diseases like epidermolysis bullosa simplex, where skin becomes fragile and blisters easily, illustrating the importance of intermediate filaments in tissue integrity.

Reason:
Intermediate filaments are critical for maintaining tissue and organ integrity, and their study is important in dermatology, neurology, and cancer biology, as they serve as diagnostic markers for certain tumors (e.g., cytokeratins) and are involved in diseases like muscular dystrophy and neurodegenerative disorders.

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📝 All Intermediate filaments structure and function MCQs

Q1. A cell must withstand repeated mechanical stretching without losing its overall shape. Which cytoskeletal feature would contribute most directly to this resistance, and why?

A.A network of highly dynamic filaments that rapidly depolymerizes

B.A network of strong rope-like fibers that distributes tensile stress ✅

C.A membrane-bound lipid layer that prevents protein movement

D.A network composed exclusively of motor proteins

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: Intermediate filaments are specialized for mechanical strength. Their rope-like architecture and relatively stable organization allow tensile forces to be distributed across the cell, helping cells resist stretching, deformation, and mechanical stress without requiring rapid filament turnover.

Q2. Two cells contain similar amounts of actin and tubulin, but Cell X contains substantially more intermediate-filament protein. Cell X is repeatedly compressed and stretched. What outcome is most reasonable?

A.Cell X should generally tolerate mechanical deformation better ✅

B.Cell X should lose its plasma membrane immediately

C.Cell X should become unable to perform any intracellular transport

D.Cell X should have no cytoskeletal organization

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Intermediate filaments provide structural reinforcement rather than serving primarily as tracks for intracellular transport or rapid shape changes. A greater intermediate-filament network can therefore improve resistance to mechanical deformation.

Q3. A researcher observes that a filament system remains intact for long periods but can still be reorganized when cells undergo major structural changes. Which interpretation best fits intermediate filaments?

A.They are completely permanent and cannot be modified

B.They are highly unstable and continuously disappear

C.They combine substantial structural stability with regulated remodeling ✅

D.They are composed only of membrane lipids

💡 Difficulty: medium | ✅ Correct: C

📖 Explanation: Intermediate filaments are generally more stable than microtubules and actin filaments, but stability does not mean absolute permanence. Cells can regulate their organization and remodeling during processes such as division, migration, and differentiation.

Q4. A mutation weakens intermediate-filament interactions in epithelial cells. The cells initially look normal, but repeated mechanical stress causes cell rupture. Which chain of reasoning best explains the observation?

A.Weakened filaments reduce tensile support, mechanical stress becomes concentrated, and structural failure becomes more likely ✅

B.Weakened filaments increase ATP production, causing membrane rupture

C.Weakened filaments increase DNA replication, producing excessive pressure

D.Weakened filaments prevent all protein synthesis, immediately killing the cells

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: Intermediate filaments form mechanically resilient networks that help distribute forces through cells and tissues. If their interactions are weakened, stress can become concentrated at vulnerable regions, so repeated deformation can eventually cause structural damage.

Q5. A scientist mistakenly concludes: "Because intermediate filaments are more stable than actin, they must be completely incapable of rearrangement." Which correction is most scientifically defensible?

A.Stability means the filaments never interact with other proteins

B.Stability describes resistance to rapid turnover, while cells can still regulate filament organization ✅

C.Intermediate filaments are actually membrane carbohydrates

D.Only tubulin can ever undergo cytoskeletal remodeling

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: The conclusion confuses relative stability with absolute immobility. Intermediate filaments generally resist rapid assembly and disassembly, yet their networks can be reorganized through regulated changes in filament-associated proteins and cellular processes.

Q6. A researcher blocks a protein required for proper intermediate-filament organization. The cell still produces normal amounts of actin and tubulin but becomes unusually fragile. Which conclusion is strongest?

A.Actin and tubulin must be chemically converted into intermediate filaments

B.Intermediate filaments have a distinct structural role that cannot be fully replaced by other cytoskeletal systems ✅

C.Intermediate filaments are unnecessary when actin is present

D.Tubulin normally performs only extracellular functions

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: Different cytoskeletal systems have overlapping but distinct functions. Actin and microtubules cannot completely substitute for the mechanical reinforcement supplied by intermediate filaments, explaining why normal amounts of other cytoskeletal proteins may not prevent fragility.

Q7. A graph records the percentage of cells remaining structurally intact after repeated mechanical stress. Group A decreases from 95% to 55%, whereas Group B decreases from 94% to 88%. Group B has increased intermediate-filament expression. What inference is best supported?

A.Intermediate filaments likely improve resistance to repeated mechanical stress ✅

B.Intermediate filaments eliminate all forms of cellular damage

C.Intermediate filaments are responsible for producing ATP

D.Intermediate filaments prevent every type of cell signaling

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The two groups begin with similar integrity, but the group with increased intermediate-filament expression retains a much larger fraction of intact cells after repeated stress. This pattern supports a role for intermediate filaments in mechanical resilience.

Q8. A drug causes rapid microtubule depolymerization but leaves intermediate filaments largely unaffected. A cell loses efficient intracellular cargo transport but remains relatively resistant to mechanical stretching. What does this comparison demonstrate?

A.All cytoskeletal systems perform exactly the same function

B.Intermediate filaments are specialized for mechanical support, whereas microtubules are important for transport organization ✅

C.Microtubules are responsible only for mechanical strength

D.Intermediate filaments function exclusively as intracellular transport tracks

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: Microtubules provide organized tracks that support movement of intracellular cargo, while intermediate filaments are particularly important for mechanical stability. The contrasting effects of the drug reveal functional specialization among cytoskeletal systems.

Q9. A scientist compares two tissues. Tissue P experiences frequent stretching, while Tissue Q experiences little mechanical stress but requires rapid changes in cell shape. If their intermediate-filament abundance differs, which prediction is most reasonable?

A.Tissue P may benefit from stronger intermediate-filament networks, whereas Tissue Q may rely relatively more on dynamic cytoskeletal systems ✅

B.Tissue P should contain no cytoskeletal proteins

C.Tissue Q must contain only intermediate filaments

D.Both tissues must have identical cytoskeletal composition regardless of function

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: Cytoskeletal composition reflects cellular demands. Tissues exposed to substantial mechanical stress often require strong intermediate-filament networks, whereas cells requiring rapid shape changes depend heavily on more dynamic systems such as actin.

Q10. A cell biologist argues that intermediate filaments are mainly responsible for generating the force that drives chromosome movement during cell division. Which evaluation is most appropriate?

A.Correct, because intermediate filaments are the primary chromosome-moving motors

B.Incorrect, because microtubules and associated proteins have the major role in chromosome movement ✅

C.Correct, because intermediate filaments directly synthesize ATP

D.Incorrect, because chromosomes move only through actin contraction

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: Chromosome movement during cell division depends primarily on the mitotic spindle formed from microtubules and associated proteins. Intermediate filaments instead contribute strongly to cellular structural integrity and are reorganized during division.

Q11. A hypothetical intermediate-filament protein forms unusually weak lateral interactions but normal individual subunits. A model predicts that filaments assemble but fail under modest tension. Which explanation best connects molecular structure to cellular behavior?

A.Weak lateral interactions can reduce filament cohesion, producing networks that assemble but transmit mechanical forces poorly ✅

B.Weak lateral interactions necessarily increase chromosome replication

C.Normal subunits guarantee mechanically perfect filaments

D.Lateral interactions affect only membrane lipid synthesis

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Intermediate-filament strength depends on how subunits associate into durable higher-order structures. If lateral interactions are weakened, filaments may still form, but their overall cohesion and ability to distribute tensile forces can be substantially reduced.

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