In a tissue, cells are bound together by physical attachment between cell to cell or between cell to the extracellular matrix. The following are some of the characteristics of cell junctions: A. Tight junctions are cell-cell junctions connecting the intermediate filament in one cell with that in the adjacent cell. B. Desmosomes are cell-matrix anchoring junctions connecting actin filament in one cell to the extracellular matrix. C. Gap junctions are channel-forming junctions allowing the passage of small water-soluble molecules from cell to cell. D. Tight junctions are occluding junctions that seal the gap between two cells. E. Hemidesmosomes are cell-matrix anchoring junctions connecting intermediate filaments in one cell to the extracellular matrix. Which one of the following options represents the combination of ALL INCORRECT statements?
A and B
Cell Junctions and Tissue Structure
In multicellular organisms, cells within tissues are held together and organized by specialized structures called cell junctions. These junctions provide mechanical support, regulate paracellular permeability, and facilitate communication between cells or between cells and the extracellular matrix. The question asks us to identify the incorrect statements regarding different types of cell junctions.
Let's examine each statement provided:
- Statement A: Tight junctions are cell-cell junctions connecting the intermediate filament in one cell with that in the adjacent cell.
Tight junctions primarily function to seal the gap between adjacent epithelial cells, preventing the passage of molecules through the paracellular space. They are composed of proteins like claudins and occludins. They are not involved in connecting intermediate filaments between cells. Intermediate filaments are typically linked across cells by desmosomes.
Therefore, statement A is incorrect.
- Statement B: Desmosomes are cell-matrix anchoring junctions connecting actin filament in one cell to the extracellular matrix.
Desmosomes are strong cell-cell anchoring junctions, not cell-matrix junctions. They connect the intermediate filament cytoskeletons (specifically keratins in epithelial cells) of adjacent cells. Cell-matrix anchoring junctions linking to intermediate filaments are called hemidesmosomes, and those linking to actin filaments are called focal adhesions.
Therefore, statement B is incorrect.
- Statement C: Gap junctions are channel-forming junctions allowing the passage of small water-soluble molecules from cell to cell.
Gap junctions are indeed channel-forming cell-cell junctions. They consist of protein complexes called connexons, which create pores that allow the passage of small molecules (like ions, sugars, amino acids) and electrical signals directly between the cytoplasm of adjacent cells.
Therefore, statement C is correct.
- Statement D: Tight junctions are occluding junctions that seal the gap between two cells.
Tight junctions are also known as occluding junctions because they create a seal between adjacent cells, preventing leakage across epithelial sheets. This is a primary function of tight junctions, helping to maintain cell polarity and separate fluid compartments.
Therefore, statement D is correct.
- Statement E: Hemidesmosomes are cell-matrix anchoring junctions connecting intermediate filaments in one cell to the extracellular matrix.
Hemidesmosomes are cell-matrix junctions found at the basal surface of epithelial cells. They firmly anchor the cell to the underlying basal lamina (part of the extracellular matrix). They connect the intermediate filaments (keratins) inside the cell to extracellular matrix components like laminin via integrin receptors.
Therefore, statement E is correct.
Based on the analysis, the incorrect statements are A and B.
We need to find the option that represents the combination of ALL incorrect statements. The incorrect statements are A and B.
Let's check the given options:
- Option 1: A and B (A is incorrect, B is incorrect)
- Option 2: B and D (B is incorrect, D is correct)
- Option 3: C and E (C is correct, E is correct)
- Option 4: D and E (D is correct, E is correct)
The combination of ALL incorrect statements is A and B.
Important Questions from Cellular communication
In a neuron, proteins and membranes are primarily synthesized in the cell body. These materials must be transported down the axon to the synaptic region using microtubules in an anterograde fashion. Such axonal transport is directed by
Acetylcholine is a potent neurotransmitter, which is released from the neurons. After release they diffuse across the synaptic cleft and combine with nicotinic acetylcholine receptor molecules in the membrane of the postsynaptic cell. The interaction of acetylcholine with the nicotinic acetylcholine receptor produces large transient increase in the permeability of the membrane to specialized ions resulting in signal transduction for nerve impulse. Acetylcholine receptor is a
Column X represents the type of junctions and column Y represents the proteins associated with the junctions.
Column X
Column Y
A.
Anchoring junction
i.
Claudins
B.
Occluding junction
ii.
Delta-Notch
C.
Channel-forming junction
iii.
Desmoglein
D.
Signal-relaying junction
iv.
Connexin
Which one of the following options is a correct match between terms of Columns X and Y?
Bacteria employ various mechanisms to invade or enter host cells, which are either phagocytic or non-phagocytic in nature. Given below are some of the mechanisms which are generally used for carrying out this process.
A. Some bacteria express a protein called invasin that is recognized by host-cell β1 integrins.
B. Actin polymerization along with assembly of clathrin coat results in the internalization of bacteria by zipper mechanism.
C. Some bacteria, including Salmonella enterica, use trigger mechanism to inject a set of effector molecules in the cytosol through type III secretion system.
D. Some bacteria attach to host cell surface receptors inducing local elevation of Ca2+ in cell cytosol, leading to the fusion of lysosomes with bacteria containing plasma membrane vesicles.
Which one of the following represents the combination of correct mechanisms for invading non-phagocytic cells?
In C. elegans, PAR proteins segregate at the cell cortex in the zygote to establish cell polarity. This is dependent on the regulation of the cortical actin cytoskeleton by RhoA. An investigator sought to directly inhibit actin polymerization to analyze the impact of this inhibition on PAR protein localization. Which one of the following chemicals would be the most suitable?
