Question 1

Which of the following statements best describes the primary function of tight junctions in epithelial cells?

Accepted Answer

They form a barrier that seals off body cavities and controls the passage of solutes and ions across the epithelial layer.

Question 2

A researcher is studying a mutation that disrupts the function of E-cadherin in epithelial cells. Which of the following cellular processes is most likely to be directly affected?

Accepted Answer

Adherens junction-mediated cell-cell adhesion

Question 3

Which of the following cell adhesion molecules (CAMs) is most directly involved in binding to oligosaccharide molecules on neighboring cells during leukocyte extravasation?

Accepted Answer

Selectins

Question 4

Gap junctions are composed of which integral membrane protein, and what is the structural organization of the channel?

Accepted Answer

Connexin; six subunits arranged in a ring to form a connexon

Question 5

A patient has a genetic defect in the integrin β subunit. Which of the following cellular functions is most likely to be impaired?

Accepted Answer

Cell-matrix adhesion and signal transduction from the extracellular matrix

Question 6

Which of the following best explains why desmosomes are important in tissues subject to mechanical stress, such as the skin and heart?

Accepted Answer

They connect intermediate filaments of adjacent cells, providing strong mechanical coupling.

Question 7

Which of the following is a key difference between homophilic and heterophilic interactions of CAMs?

Accepted Answer

Homophilic interactions involve the same type of CAM on both cells, while heterophilic interactions involve different CAMs or molecules on each cell.

Question 8

Which of the following proteins is NOT directly involved in the structure or function of tight junctions?

Accepted Answer

Connexin

Question 9

A scientist observes that certain epithelial cells lose their polarity and allow unregulated movement of solutes across the layer. Which junction is most likely defective?

Accepted Answer

Tight junctions

Question 10

Which of the following best describes the role of hemidesmosomes in epithelial cells?

Accepted Answer

They anchor epithelial cells to the underlying extracellular matrix via intermediate filaments.

Question 11

Which of the following statements about gap junctions is correct?

Accepted Answer

They allow diffusion of molecules with a molecular mass below approximately 1000 daltons.

Question 12

Which of the following is a unique feature of plasmodesmata in plant cells compared to gap junctions in animal cells?

Accepted Answer

They are lined by plasma membrane and contain a central desmotubule.

Question 13

A mutation in the gene encoding desmoglein would most likely disrupt which of the following?

Accepted Answer

Desmosome-mediated cell-cell adhesion

Question 14

Which of the following best describes the molecular mechanism by which selectins mediate cell-cell adhesion?

Accepted Answer

They bind to oligosaccharide molecules on glycoproteins of neighboring cells via their lectin domain.

Question 15

Which of the following equations best represents the relationship for the diffusion of molecules through a gap junction, assuming the channel is open and the concentration gradient is the driving force?

Accepted Answer

$J = -D \, \frac{dC}{dx}$

Question 16

Which of the following is a function of the cytosolic domain of cadherins in adherens junctions?

Accepted Answer

Interacting with adaptor proteins such as $ \alpha $-catenin and $ \beta $-catenin to link to the actin cytoskeleton

Question 17

Which of the following scenarios best illustrates a heterotypic adhesion?

Accepted Answer

An epithelial cell interacting with a connective tissue cell via different CAMs

Question 18

Which of the following is a key function of anchoring junctions in tissues?

Accepted Answer

Imparting strength and rigidity to tissues by connecting cytoskeletal elements of adjacent cells

Question 19

A scientist is studying a tissue where the movement of ions and small molecules between adjacent cells is blocked, but the cells remain mechanically connected. Which junction is most likely non-functional?

Accepted Answer

Gap junctions

Cellular Communication and Cell Junctions: Structure and Function

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