38 Questions
What is the primary function of tight junctions?
To restrict the diffusion of solutes larger than 1.8 nm in diameter
What is the role of Claudins and occludins in tight junctions?
They bind to similar proteins on adjacent cells, sealing the intercellular space
What is the blood-brain barrier responsible for?
Preventing the passage of substances from blood to the brain
What is the result of claudin 16 mutations?
Hypomagnesemia and impaired reabsorption of Mg and Ca
What is the function of zonula occludens (ZO) proteins?
They link the tight junction to the actin cytoskeleton
What is the result of inflammatory states such as meningitis on the blood-brain barrier?
It reduces the integrity of the blood-brain barrier
What is the primary function of endothelial cells in the brain and spinal cord?
To form a physical barrier, separating the blood from the nervous tissue
What is the result of tight junctions between endothelial cells in the brain and spinal cord?
It creates a physical barrier, separating the blood from the nervous tissue
Desmosomes contain plaque shaped structures on the _______ face of the junction.
cytoplasmic
Which of the following is NOT a plaque protein in desmosomes?
Laminin
What is the main function of desmosomes in tissues?
To provide mechanical strength
In which of the following tissues are desmosomes especially abundant?
Epidermis
What is the name of the autoimmune disease that affects desmosomal cadherins?
Pemphigus
What is the result of the disruption of desmosomes in pemphigus?
Severe blistering of the skin
What type of intermediate filaments are found in epithelial cells?
Keratin filaments
What determines the type of intermediate filaments found in a cell?
Cell type
What type of junction is characterized by the presence of a single dense plaque on the cytoplasmic surface?
Hemidesmosome
Which protein binds to keratin intermediate filaments in hemidesmosomes?
Plectin
What is the main function of hemidesmosomes?
Cell-matrix adhesion
Which disease is caused by autoantibodies attacking type XVII collagen?
Bullous pemphigoid
What type of junction allows for direct communication between cells?
Gap Junction
Which of the following tissues does NOT have gap junctions?
Nerve tissue
Which of the following is a function of anchoring junctions?
To provide cell-cell adhesion and bind cytoskeleton to the cell surface
Which claudin gene mutation is associated with hereditary deafness?
Claudin-14
What is the primary function of adherens junctions?
To hold cells together and maintain physical integrity of the epithelium
Which of the following proteins is involved in binding cytoskeleton to the cell surface?
Vinculin
What is the location of adherens junctions in epithelial cells?
Near the apical surface
Which type of junction is an anchorage site for actin filaments?
Adherens junctions
Which of the following is a type of anchoring junction?
Desmosome
Which claudin gene mutations are associated with this syndrome?
Claudin-16 and 19
What is the primary function of gap junctions?
To allow for the free interchange of ions and larger molecules
What is the diameter of the molecules that can pass through gap junctions between mammalian cells?
1.2 nm
What is the mechanism by which gap junctions are regulated?
Posttranslational modification of connexins
What is the term for the small intracellular signaling molecules that can pass through gap junctions?
Second messengers
What is the width of the intercellular space between plasma membranes of adjoining cells?
20 A⁰
What is the structure of gap junctions that allows for the formation of a hydrophilic channel?
Tube-like protein structures
What is the term for the protein subunits that make up a connexon?
Connexins
What is the effect of a decrease in pH and an increase in Ca ions on the permeability of gap junctions?
Decrease the permeability
Study Notes
Tight Junctions
- Restrict the diffusion of solutes larger than 1.8 nm in diameter
- Prevent the passage of water-soluble substances
- Formed by transmembrane proteins, such as claudins and occludins, that bind to similar proteins on adjacent cells
- Associate with intracellular proteins of zonula occludens (ZO) to link to the actin cytoskeleton
- Responsible for the blood-brain barrier and blood-testes barrier
Blood-Brain Barrier
- Formed by endothelial cells of capillaries in the brain and spinal cord joined by continuous tight junctions
- Separates the blood from the nervous tissue
- Prevents the passage of substances from the blood to the brain
- Helps to protect the brain, but also creates difficulties in treating brain disorders
Anchoring Junctions (Adhering Junctions)
- Composed of two classes of proteins: transmembrane adhesion proteins (cadherins) and intracellular anchor proteins (vinculin, alpha-actinin, catenin, desmoplakin)
- Functions: cell-to-cell adhesion and binding of cytoskeleton to the cell surface
- Found in two forms: adherens junctions (zonula adherens) and desmosomes
Adherens Junctions (Zonula Adherens)
- Surround the entire periphery of epithelial cells near their apical surface
- Form adhesion belts that link neighboring cells together
- Maintain the physical integrity of the epithelium
- Found in heart muscle, where it is called fascia adherens, connecting cardiomyocytes together
Desmosomes
- Contain plaque-shaped structures on the cytoplasmic face of the junction
- Provide attachment sites for intermediate filaments
- Contain desmoglein and desmocollin, which link adjacent cells together
- Found in skin, heart muscle, and the neck of the uterus
- Important for mechanical strength in tissues
Hemidesmosomes
- Resemble desmosomes morphologically
- Cell uses hemidesmosomes to attach to the basal lamina
- Contain integrins that bind to laminin in the basal lamina and anchor to keratin intermediate filaments
- Important for attachment to the extracellular matrix
Channel-Forming Junctions (Communicating Junctions)
- Gap junctions: allow for the free interchange of ions and larger molecules between cells
- Found in almost all tissues, except for skeletal muscle cells and blood cells
- Physiologic experiments demonstrate that fluorescent dyes can pass into neighboring cells
Gap Junctions
- Consist of assemblies of six connexins, which form a hydrophilic channel
- Allow for the passage of ions, amino acids, nucleotides, sugars, and cyclic AMP
- Permeability is regulated by posttranslational modification of connexins
- Serve as direct connections between the cytoplasm of adjacent cells
- Permit the passage of molecules up to 1.2 nm in diameter
This quiz covers the structure and function of tight junctions in cell membranes, including their role in restricting the diffusion of solutes and water-soluble substances.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
