MCAT Biological and Biochemical Foundations of Living Systems Quiz: 2a Cell Cell Junctions Ecm

What this quiz covers

This quiz focuses on 2a Cell Cell Junctions Ecm, giving you a quick way to practice the rules, question types, and explanations that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Paracellular barrier function is compromised while transcellular transporter trafficking can remain intact, indicating selective disruption of tight junctions (correct answer)
2. Transcellular nutrient uptake must decrease because tight junction proteins directly form nutrient transporter pores
3. Cell–cell mechanical adhesion must fail because claudins are the primary cadherins that link actin between adjacent cells
4. Cell–ECM attachment must increase because tight junction loss upregulates integrin binding, raising TEER

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Tight junctions create paracellular barriers through transmembrane proteins like occludin and claudins, while transcellular transport occurs through specific transporters and is regulated independently. In this vignette, cytokine-induced internalization of tight junction proteins reduces barrier function without affecting transporter endocytosis. Choice A is correct because tight junction disruption specifically compromises the paracellular barrier (decreased TEER) while transcellular transport mechanisms remain functional, as evidenced by unchanged nutrient transporter trafficking. Choice B is incorrect as tight junction proteins form paracellular barriers, not nutrient transporter pores, and transcellular transport uses distinct membrane proteins. Understanding that paracellular and transcellular pathways are independently regulated helps predict how specific perturbations affect epithelial function.

Question 2

1. Failure of integrin-mediated focal adhesions decreases cell–substrate binding, causing detachment rather than intercellular tearing
2. Failure of tight junction sealing increases paracellular permeability, leading to osmotic swelling and tearing
3. Failure of gap junction communication prevents calcium diffusion, directly weakening the extracellular matrix
4. Failure of desmosome-mediated linkage to intermediate filaments reduces resistance to mechanical stress at cell–cell contacts (correct answer)

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Desmosomes are specialized adhesive junctions that link intermediate filaments between cells through desmosomal cadherins like desmoglein, providing mechanical strength to tissues under stress. In this vignette, reduced desmoglein expression specifically compromises desmosome function while other junctions remain normal. Choice D is correct because desmosomes are the primary junctions responsible for resisting mechanical stress by anchoring intermediate filaments, and their disruption explains why the monolayer tears at cell-cell boundaries under stretch. Choice B is incorrect as normal tight junction localization indicates barrier function is intact, and tight junctions don't primarily provide mechanical strength. The specific tearing at cell-cell boundaries rather than cell detachment confirms the defect is in intercellular adhesion (desmosomes) rather than cell-substrate adhesion (integrins).

Question 3

1. Loss of laminin–integrin signaling strengthens desmosomes, forcing cells into clusters by increasing intermediate filament tension
2. Loss of laminin–integrin signaling primarily blocks paracellular sealing by tight junctions, which directly determines acinar lumen formation
3. Loss of laminin–integrin signaling increases gap junction coupling, causing disorganization by equalizing intracellular ion concentrations
4. Loss of laminin–integrin signaling disrupts cell–ECM cues needed for polarity and organized tissue architecture despite preserved cell–cell adhesion protein expression (correct answer)

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Laminin in basement membranes provides crucial positional cues through integrin binding that establish and maintain epithelial polarity and tissue architecture in 3D environments. In this vignette, blocking laminin-binding integrins disrupts normal acinar morphogenesis despite preserved cell-cell adhesion proteins. Choice D is correct because laminin-integrin signaling provides essential ECM-derived cues for establishing apical-basal polarity and organizing cells into hollow structures; without these signals, cells form disorganized clusters despite maintaining cell-cell adhesion capability. Choice B is incorrect as the primary defect is in ECM signaling for polarity, not tight junction sealing, and lumen formation requires proper polarization cues beyond just barrier function. The maintenance of E-cadherin expression confirms that cell-cell adhesion machinery is intact, highlighting the specific requirement for ECM signals in tissue organization.

Question 4

1. Blocking the collagen-binding integrin enhanced gap junction coupling, synchronizing movement and thereby reducing single-cell speed
2. Blocking the collagen-binding integrin primarily disrupted tight junction sealing, increasing paracellular leak and slowing migration
3. Blocking the collagen-binding integrin increased desmosome assembly, immobilizing cells by strengthening intermediate filaments
4. Blocking the collagen-binding integrin reduced focal adhesion formation on collagen I, limiting traction needed for migration (correct answer)

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Integrins are transmembrane receptors that bind specific ECM proteins and link them to the actin cytoskeleton, forming focal adhesions that generate traction forces necessary for cell migration. In this vignette, blocking the collagen-binding integrin specifically prevents cell-ECM interactions on collagen I surfaces. Choice D is correct because integrin-collagen binding is essential for focal adhesion formation on collagen substrates, and without these adhesions, cells cannot generate the traction forces needed for migration. Choice B is incorrect as integrins mediate cell-ECM, not cell-cell interactions, and do not directly affect tight junctions. The specificity of the effect (only on collagen I, not laminin) and unchanged cell-cell contacts confirm that the mechanism involves direct ECM-integrin interactions rather than secondary effects on cell junctions.

Question 5

1. Reduced linkage of cadherins to the actin cytoskeleton impairs adherens junction maturation, secondarily preventing robust tight junction organization (correct answer)
2. Increased desmosome assembly compensates for cadherin truncation, restoring tight junction belts and stable polarity
3. Primary loss of integrin binding to ECM prevents E-cadherin extracellular binding, explaining unstable cell–cell adhesion
4. Primary loss of gap junction conductance prevents cadherin clustering, explaining punctate tight junction proteins

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). E-cadherin's cytoplasmic tail links to the actin cytoskeleton through catenins, and this linkage is essential for adherens junction maturation and subsequent establishment of other junctional complexes. In this vignette, deleting E-cadherin's cytoplasmic tail prevents stable adherens junction formation despite intact extracellular binding. Choice A is correct because the cadherin-actin linkage is required for adherens junction maturation, which must occur before tight junctions can properly organize into continuous belts; without this, cells maintain only transient adhesions and tight junction proteins remain punctate. Choice C is incorrect as the defect is in cadherin-actin coupling, not integrin-ECM binding, and E-cadherin's extracellular domain remains functional. The sequential assembly of junctional complexes means that defective adherens junctions prevent proper tight junction organization.

Question 6

1. Disrupting cadherin adhesion destabilizes adherens junctions and secondarily impairs tight junction organization (correct answer)
2. Disrupting cadherin adhesion selectively blocks connexin pore formation without affecting other junctions
3. Chelating calcium strengthens tight junction sealing by promoting claudin polymerization
4. Chelating calcium primarily breaks hemidesmosomes, causing loss of apical junction proteins

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the interdependence of adherens and tight junctions in epithelial cells is examined. Choice A is correct because it accurately describes how disrupting cadherin adhesion destabilizes adherens junctions and impairs tight junction organization, as evidenced by β-catenin redistribution and discontinuous claudin staining. Choice C is incorrect as it mistakenly suggests calcium chelation strengthens tight junctions, a common misconception since calcium is required for cadherin function. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as barrier defects in inflammatory conditions.

Question 7

1. Hyaluronan effects require gap junction closure to prevent metabolite sharing between cells
2. Hyaluronan reduces proliferation by strengthening tight junctions that prevent growth factor entry
3. CD44 blockade restores proliferation by increasing desmosome assembly and tissue tensile strength
4. ECM glycosaminoglycan content can regulate cell cycle behavior through receptor-mediated signaling independent of cell–cell junction number (correct answer)

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the influence of ECM glycosaminoglycan on chondrocyte proliferation is examined. Choice D is correct because it accurately describes how high hyaluronan regulates cell cycle via CD44 signaling independently of junction number, as blockade restores proliferation. Choice B is incorrect as it confuses ECM with tight junctions, a common misconception since hyaluronan signals, not seals. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as in cartilage maintenance.

Question 8

1. Increased paracellular permeability because adherens junctions primarily create diffusion pores
2. Decreased basement membrane attachment because cadherins compete with integrins for ECM binding
3. Increased cell–cell adhesion that limits dissociation from the primary cluster, reducing invasive migration (correct answer)
4. Increased intercellular metabolite exchange because cadherins form connexon-like channels

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the impact of E-cadherin on carcinoma cell invasion through a collagen matrix is examined. Choice C is correct because it accurately describes how restoring E-cadherin increases cell–cell adhesion, limiting dissociation and invasive migration as observed in the Boyden chamber assay. Choice B is incorrect as it confuses cadherins with integrins, a common misconception since cadherins mediate cell–cell, not cell–ECM adhesion. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as enhanced metastasis in low E-cadherin tumors.

Question 9

1. Hemidesmosome-mediated anchoring of keratin intermediate filaments to the basement membrane. (correct answer)
2. Tight junction sealing that restricts paracellular water movement across the epidermis.
3. Gap junction communication that synchronizes keratinocyte proliferation across the tissue.
4. Adherens junction cadherin clustering that links actin networks between neighboring keratinocytes.

Explanation: This question tests understanding of cell-cell junctions and ECM in cellular organization (Foundational Concept 2). Hemidesmosomes are specialized cell-ECM junctions that anchor epithelial cells to the basement membrane through integrin α6β4, connecting keratin intermediate filaments to laminin in the ECM. In this vignette, reduced α6β4 integrin with normal E-cadherin indicates specific hemidesmosome dysfunction. Choice A is correct because hemidesmosomes provide the critical attachment between basal keratinocytes and the basement membrane, and their disruption causes dermal-epidermal separation characteristic of blistering disorders. Choice B is incorrect as tight junctions regulate paracellular permeability, not basement membrane attachment. Understanding epithelial architecture requires recognizing that hemidesmosomes anchor cells to ECM while desmosomes connect cells laterally.

Question 10

1. Reduced claudin-1 primarily weakens desmosome-mediated mechanical coupling, increasing shear-induced cell loss and secondarily raising dextran flux.
2. Reduced claudin-1 disrupts tight junction strand integrity, increasing paracellular permeability without requiring changes in adherens junctions. (correct answer)
3. Reduced claudin-1 decreases gap junction conductance, lowering TEER by limiting ion movement through connexons between cells.
4. Reduced claudin-1 strengthens apical–basal polarity cues, tightening the paracellular seal and thereby increasing TEER.

Explanation: This question tests understanding of cell-cell junctions and ECM in cellular organization (Foundational Concept 2). Tight junctions, composed of proteins like claudins and occludins, form selective barriers that regulate paracellular permeability between epithelial cells. In this vignette, reducing claudin-1 expression specifically impairs tight junction integrity while leaving adherens junctions (E-cadherin) intact. Choice B is correct because claudin-1 is a key structural component of tight junction strands, and its reduction directly increases paracellular permeability to ions (lowering TEER) and small molecules (increasing dextran flux). Choice A is incorrect as it confuses tight junctions with desmosomes, which provide mechanical strength rather than permeability control. To verify understanding, remember that tight junctions control paracellular transport while adherens junctions and desmosomes provide mechanical adhesion.

Question 11

1. Immediate loss of paracellular barrier function due to direct disassembly of claudin-occludin tight junction strands.
2. Rapid weakening of cell–cell cohesion with delayed barrier changes because tight junction sealing is not the first interaction disrupted. (correct answer)
3. Selective loss of electrical coupling while mechanical cohesion remains intact because connexin channels require Ca$^{2+}$ to open.
4. Enhanced resistance to detachment because cadherin disruption increases integrin affinity for ECM proteins.

Explanation: This question tests understanding of cell-cell junctions and ECM in cellular organization (Foundational Concept 2). Adherens junctions rely on calcium-dependent cadherin interactions for cell-cell adhesion, while tight junctions form the paracellular barrier independently. In this vignette, calcium chelation disrupts cadherin-based adherens junctions first, causing cell rounding and detachment. Choice B is correct because adherens junctions are rapidly disrupted by calcium removal, weakening cell cohesion, but tight junction barrier function persists temporarily since it doesn't directly require extracellular calcium for maintenance once formed. Choice A is incorrect as it suggests immediate tight junction disruption, which doesn't match the delayed barrier changes observed. This demonstrates the functional hierarchy where adherens junctions provide mechanical adhesion while tight junctions independently maintain barrier function.

Question 12

1. Increased ECM stiffness enhances integrin-based adhesion and cytoskeletal tension, promoting YAP nuclear localization. (correct answer)
2. Increased ECM stiffness reduces integrin engagement, decreasing actin tension and passively driving YAP into the nucleus.
3. ECM stiffness primarily alters paracellular sealing by tightening claudin-based junctions, which increases YAP nuclear localization.
4. ECM stiffness changes ligand diffusion through gap junctions, increasing YAP nuclear localization by improving intercellular metabolite exchange.

Explanation: This question tests understanding of cell-cell junctions and ECM in cellular organization (Foundational Concept 2). The extracellular matrix provides not only structural support but also mechanical cues that cells sense through integrin receptors, influencing cellular behavior and gene expression. In this vignette, ECM stiffness affects cell spreading and YAP localization, a key mechanotransduction pathway. Choice A is correct because increased ECM stiffness enhances integrin clustering and focal adhesion formation, generating cytoskeletal tension that promotes YAP nuclear translocation where it acts as a transcriptional coactivator. Choice B is incorrect as it suggests the opposite - stiff substrates actually increase, not reduce, integrin engagement and actin tension. Understanding mechanotransduction requires recognizing that cells actively sense and respond to ECM mechanical properties through integrin-cytoskeleton linkages.

Question 13

1. Poly-D-lysine supports outgrowth through basement membrane assembly that substitutes for laminin
2. Laminin promotes outgrowth by forming tight junctions that polarize neuronal membranes
3. RGD reduces outgrowth by blocking cadherin-dependent adherens junctions between neurons
4. Laminin promotes outgrowth via specific integrin-mediated signaling rather than nonspecific surface adhesion (correct answer)

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the influence of laminin on neuronal outgrowth via integrins is examined. Choice D is correct because it accurately describes how laminin promotes outgrowth through integrin-mediated signaling, as RGD blockade affects laminin but not nonspecific adhesion. Choice B is incorrect as it confuses ECM with tight junctions, a common misconception since neurons lack typical epithelial junctions. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as in neural development disorders.

Question 14

1. Greater reliance on gap junction conductance to replace traction forces during migration
2. Greater reliance on tight junction sealing to increase tissue barrier and promote movement
3. Greater reliance on desmosomes to increase intermediate filament coupling for rapid crawling
4. Greater reliance on integrin-mediated cell–ECM adhesion to generate traction forces on fibronectin (correct answer)

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the shift during EMT toward ECM-dependent migration is examined. Choice D is correct because it accurately describes greater reliance on integrin–ECM adhesion for traction when cell–cell junctions are reduced, supporting increased migration on fibronectin. Choice B is incorrect as it confuses ECM adhesion with tight junctions, a common misconception since EMT reduces junctions to enable motility. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as in cancer invasion.

Question 15

1. Loss of synchronized electrical activity due to disrupted connexin channels in keratinocytes
2. Loss of paracellular barrier due to disrupted claudin-based tight junction sealing in the epidermis
3. Loss of basal attachment due to disrupted integrin binding to laminin at hemidesmosomes
4. Loss of cell–cell mechanical cohesion within the tissue due to disrupted desmosomal adhesion (correct answer)

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the effect of desmoglein antibodies on epidermal integrity in blistering disease is examined. Choice D is correct because it accurately describes how disrupted desmosomal adhesion causes loss of cell–cell mechanical cohesion, leading to intraepidermal separation. Choice B is incorrect as it confuses desmosomes with tight junctions, a common misconception since desmosomes provide strength, not barriers. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as in autoimmune skin disorders.

Question 16

1. E-cadherin primarily anchors cells to laminin via integrins to prevent detachment from the ECM
2. E-cadherin primarily forms paracellular diffusion barriers by sealing the apical membrane domain
3. E-cadherin primarily enables electrical coupling by forming intercellular channels for ions
4. E-cadherin–based adherens junctions coordinate lateral adhesion needed for epithelial architecture and polarity cues (correct answer)

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the role of E-cadherin in maintaining epithelial polarity and architecture in intestinal organoids is examined. Choice D is correct because it accurately describes how E-cadherin-based adherens junctions coordinate lateral adhesion for epithelial architecture and polarity cues, as shown by loss of polarity and multilayering upon blockade. Choice B is incorrect as it confuses adherens junctions with tight junctions, a common misconception since adherens provide adhesion but not primary sealing. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as in cancer progression where E-cadherin loss promotes invasion.

Question 17

1. Hemidesmosomes regulate dye exchange by controlling paracellular solute movement across epithelia
2. Tight junction permeability regulates intercellular exchange of cytosolic dyes through connexon pores
3. Adherens junctions regulate dye exchange by forming direct aqueous channels between cells
4. Gap junction permeability regulates intercellular exchange of small molecules and can be modulated without altering barrier sealing (correct answer)

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, the role of gap junctions in facilitating intercellular communication via small molecule exchange is examined, with modulation by connexin phosphorylation. Choice D is correct because it accurately describes how gap junctions regulate the exchange of small molecules like dyes and can be modulated independently of barrier functions maintained by tight junctions, as evidenced by unchanged TEER. Choice B is incorrect as it confuses tight junctions with gap junctions, attributing connexon pores—which are specific to gap junctions—to tight junction function, a common misconception. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption, such as impaired signaling in tissues reliant on gap junction communication.

Question 18

1. Toxin-induced strengthening of adherens junctions increases small-solute leak by expanding pore size
2. Toxin-induced loss of desmosomes increases paracellular permeability only to large macromolecules
3. Toxin-induced activation of gap junctions allows selective passage of 4 kDa tracer but excludes 70 kDa dextran
4. Toxin-induced disruption of tight junction scaffolding increases paracellular permeability primarily to small solutes (correct answer)

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, toxin mislocalizes ZO-1, disrupting tight junctions in intestinal epithelium. Choice D is correct because it accurately describes increased small-solute permeability from scaffolding loss, consistent with selective tracer flux. Choice B is incorrect as it confuses tight junctions with desmosomes, a common misconception in size-selective permeability. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption in barrier epithelia.

Question 19

1. Gap junctions provide low-resistance pathways for ionic current between cells, supporting electrical conduction (correct answer)
2. Tight junctions prevent ions from moving between cells, and inhibiting them slows conduction
3. Adherens junctions form voltage-gated pores, and blocking them decreases conduction velocity
4. Hemidesmosomes transmit depolarization from cell to ECM, and inhibiting them slows conduction

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, connexin inhibition affects electrical conduction in cardiomyocytes via gap junctions. Choice A is correct because it accurately describes gap junctions enabling ionic current for conduction, consistent with slowed propagation velocity. Choice B is incorrect as it confuses gap junctions with tight junctions, a common misconception in electrical coupling. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption in excitable tissues like heart.

Question 20

1. Integrin–ECM signaling supports survival pathways and cytoskeletal organization, and inhibiting FAK weakens these outputs (correct answer)
2. Integrin–ECM binding primarily forms paracellular seals, and inhibiting FAK increases serum-dependent leakiness
3. Integrin–ECM binding primarily opens connexin pores, and inhibiting FAK reduces nutrient sharing between cells
4. Integrin–ECM binding primarily strengthens cadherin junctions, and inhibiting FAK reduces cadherin transcription

Explanation: This question tests understanding of cell–cell junctions and ECM in cellular organization (Foundational Concept 2). Cell–cell junctions like tight junctions regulate permeability, while ECM provides structural support and signaling cues. In this vignette, FAK inhibition downstream of integrins affects epithelial survival and cytoskeleton on ECM. Choice A is correct because it accurately describes integrin-ECM signaling supporting these pathways, consistent with reduced stress fibers and survival. Choice B is incorrect as it confuses integrins with paracellular sealing, a common misconception in adhesion signaling. Ensure understanding of specific junction functions and ECM roles in cellular processes; apply this to predict effects of their disruption in anchorage-dependent behaviors.