Cell-cell junctions Practice Questions
20 free Cell-cell junctions practice questions for the USMLE Step 1. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which class of cell–cell junctions primarily functions to seal adjacent epithelial cells and prevent paracellular leakage of molecules and ions?
- A Anchoring junctions
- B Adherens junctions
- C Occluding junctions
- D Gap junctions
Correct answer: Occluding junctions
Occluding junctions, also known as tight junctions (zonula occludens), seal the plasma membranes of adjacent cells to prevent paracellular passage of water and solutes, maintaining a barrier between compartments.
Which transmembrane proteins are most critically involved in the formation of tight junctions between epithelial cells?
- A Connexins
- B Integrins
- C Claudins and occludin
- D Desmoglein and desmocollin
Correct answer: Claudins and occludin
Tight junctions are formed through interactions of transmembrane proteins such as claudins and occludin between adjacent cell membranes, which generate the tight seal characteristic of occluding junctions.
Which type of cell–cell junction is characterized by direct cytoplasmic connections allowing passage of ions and small molecules between adjacent cells?
- A Desmosomes
- B Hemidesmosomes
- C Tight junctions
- D Gap junctions
Correct answer: Gap junctions
Gap junctions are communicating junctions composed of connexon channels that span the membranes of two adjacent cells, enabling direct passage of small molecules and ions between their cytoplasms.
What is the basic structural unit of a gap junction channel in vertebrate cells?
- A Two cadherin molecules from opposite cells clasping together
- B A single connexon of six connexins that pairs with no partner
- C Two connexons, each six connexins, one from each adjacent cell
- D A paired claudin and occludin protein complex
Correct answer: Two connexons, each six connexins, one from each adjacent cell
A gap junction channel is formed by a connexon (hemichannel) made of six connexin proteins in one cell membrane; when that hemichannel docks with a connexon on an adjacent cell, they form a continuous intercellular channel.
Which of the following junction types links the actin cytoskeleton of one cell to that of its neighbor, providing mechanical support and maintaining tissue integrity?
- A Hemidesmosome
- B Adherens junction
- C Tight junction
- D Gap junction
Correct answer: Adherens junction
Adherens junctions (zonula adherens) use cadherin transmembrane proteins and intracellular catenins to link the actin cytoskeleton across neighboring epithelial cells, thereby contributing to mechanical cohesion and shape maintenance.
Which type of cell junction connects intermediate filaments of adjacent cells via cadherin proteins and is prominent in tissues subject to mechanical stress (e.g., skin, myocardium)?
- A Tight junction
- B Adherens junction
- C Desmosome
- D Gap junction
Correct answer: Desmosome
Desmosomes are anchoring junctions that link intermediate filament networks of neighboring cells via cadherin family proteins (desmoglein/desmocollin), thereby providing strong mechanical adhesion especially in stress-bearing tissues.
Which specialized junction type anchors epithelial cells to the underlying basement membrane via integrin proteins and cytoplasmic intermediate filaments?
- A Adherens junction
- B Desmosome
- C Hemidesmosome
- D Gap junction
Correct answer: Hemidesmosome
Hemidesmosomes link epithelial cells to the extracellular matrix (basement membrane) through integrin transmembrane proteins anchored internally to intermediate filament cytoskeleton, providing stable attachment to the substratum.
Which of the following functions is NOT typically associated with cell–cell junctions in epithelial tissue?
- A Establishing cell polarity by restricting lateral diffusion of membrane proteins
- B Allowing free diffusion of large proteins between adjacent cell cytoplasms
- C Providing mechanical adhesion between cells
- D Controlling paracellular permeability between adjacent cells
Correct answer: Allowing free diffusion of large proteins between adjacent cell cytoplasms
Cell–cell junctions like tight junctions and gap junctions regulate permeability and selective communication; they generally do not allow free diffusion of large proteins between adjacent cell cytoplasms — only small molecules/ions can pass via gap junctions.
If a toxin disrupts claudin and occludin interactions in the epithelium, which consequence is most likely?
- A Loss of direct cytoplasmic communication between cells
- B Failure of cell-to-matrix anchoring at the basement membrane
- C Increased paracellular permeability and barrier failure
- D Loss of intermediate filament network integrity
Correct answer: Increased paracellular permeability and barrier failure
Claudin and occludin are core components of tight junctions; disruption leads to failure of the occluding seal, increasing paracellular permeability and compromising the barrier function of the epithelium.
Which junctional complex is most likely to facilitate the synchronized contraction of cardiac muscle cells by allowing rapid spread of ions between cells?
- A Tight junction
- B Desmosome
- C Adherens junction
- D Gap junction
Correct answer: Gap junction
Gap junctions permit direct ionic and metabolic coupling between adjacent cardiomyocytes, enabling the rapid spread of action potentials and synchronized contraction.
The 'terminal bar' observed under light microscopy at the apical end of epithelial cells most closely corresponds to which of the following under electron microscopy?
- A A single isolated tight junction seal
- B A single desmosome anchoring junction
- C Tight junction, adherens junction, and desmosome together
- D A cluster of gap junction channels only
Correct answer: Tight junction, adherens junction, and desmosome together
The terminal bar is a light-microscope artifact representing a complex of multiple junctional structures (tight junction, adherens junction, desmosome) at the apical lateral border of epithelial cells, which can only be resolved by electron microscopy.
Which family of proteins mediates calcium-dependent adhesion at adherens junctions and desmosomes?
- A Connexins
- B Claudins
- C Cadherins
- D Integrins
Correct answer: Cadherins
Cadherins are transmembrane adhesion molecules that mediate calcium-dependent cell–cell adhesion at adherens junctions and desmosomes, linking adjacent cells mechanically through cytoskeletal attachments.
Which of the following statements accurately distinguishes between adherens junctions and tight junctions in epithelial cells?
- A Tight junctions connect actin cytoskeletons; adherens junctions form a paracellular seal.
- B Adherens junctions give actin-based adhesion; tight junctions seal against paracellular passage.
- C Both junction types anchor intermediate filaments firmly between neighboring cells.
- D Only tight junctions permit direct intercellular diffusion of small molecules.
Correct answer: Adherens junctions give actin-based adhesion; tight junctions seal against paracellular passage.
Adherens junctions provide mechanical adhesion between cells via actin-cytoskeleton linking, while tight junctions act as occluding junctions that seal adjacent cell membranes to prevent paracellular flow.
Which type of junction would be most compromised in a disease that weakens intermediate filament linkage between epithelial cells, potentially causing blister formation under mechanical stress?
- A Tight junctions
- B Gap junctions
- C Hemidesmosomes or desmosomes
- D Adherens junctions
Correct answer: Hemidesmosomes or desmosomes
Desmosomes (and hemidesmosomes attaching to basal lamina) anchor intermediate filaments between cells or to extracellular matrix; if these attachments weaken, epithelial integrity under stress is lost, leading to blister formation, as seen in some skin diseases.
Which cell–cell junction type can be dynamically regulated (opened or closed) to modulate intercellular communication between neighboring cells?
- A Tight junctions
- B Gap junctions
- C Desmosomes
- D Hemidesmosomes
Correct answer: Gap junctions
Gap junction channels, composed of connexins, can be regulated (e.g., by phosphorylation or pH changes) to open or close, thereby controlling passage of ions and small molecules between adjacent cells.
In which scenario is a hemidesmosome most critical for normal tissue function?
- A Between two adjacent epithelial cells in the intestine for barrier function
- B Connecting basal epithelial cells to the underlying basement membrane
- C Allowing cardiac myocytes to synchronize contraction
- D Permitting paracellular diffusion of water in kidney proximal tubule
Correct answer: Connecting basal epithelial cells to the underlying basement membrane
Hemidesmosomes anchor basal epithelial cells to the basement membrane via integrin-mediated linkage to intermediate filaments — a key for stable attachment of epithelia to underlying connective tissue.
Which junctional complex is most directly responsible for maintaining apical–basal polarity of epithelial cells by restricting lateral diffusion of membrane proteins between domains?
- A Desmosomes
- B Adherens junctions
- C Tight junctions
- D Gap junctions
Correct answer: Tight junctions
Tight junctions create a barrier that prevents free diffusion of membrane proteins and lipids between the apical and basolateral domains, thus preserving epithelial cell polarity.
Which of the following statements about communicating junctions is true?
- A They use cadherins to link cytoskeletons of neighboring cells.
- B They block paracellular diffusion of small dissolved molecules.
- C They form cytoplasmic channels passing ions and small metabolites.
- D They anchor cells firmly to the surrounding extracellular matrix.
Correct answer: They form cytoplasmic channels passing ions and small metabolites.
Communicating junctions (gap junctions) consist of channel-forming connexons that directly connect cytoplasm of adjacent cells, allowing passage of ions and small metabolites — facilitating intercellular communication.
Which of the following would likely impair gap junction–mediated intercellular communication in a tissue?
- A Loss of claudin protein expression
- B Degradation of the actin cytoskeleton network
- C Mutation in connexin proteins forming connexons
- D Removal of the underlying basement membrane
Correct answer: Mutation in connexin proteins forming connexons
Gap junctions depend on connexin proteins to form connexons; mutations in connexin genes can impair formation of functional channels, thus blocking intercellular communication.
Which of the following junction types is LEAST likely to be found between adjacent endothelial cells of a leaky capillary where high permeability is required?
- A Adherens junctions
- B Desmosomes
- C Tight junctions
- D Gap junctions
Correct answer: Tight junctions
Tight junctions create tight seals — in leaky capillaries (e.g., certain fenestrated or sinusoidal endothelium) such seals are minimized to allow high permeability; thus tight junctions are reduced or absent in such areas. Anchoring and communicating junctions may still be present.