Question

The cell membranes of adjacent cells are fused at which of the following cell junctions?
A. Macula adherens
B. Zonula adherens
C. Zonula occludens
D. Nexus

Answer 1

Cell junctions, also known as intercellular bridges, are a group of cellular structures that consists of multi-protein complexes which provide contact or adhesion between neighbouring cells or between the cell and the extracellular matrix in animal cells.

Complete answer: Zonula occludens denotes tight junctions. Plasmalemma of two cells fuses and forms an impermeable or occluding junction. For instance, the epithelial cells or the capillaries and the brain cells. These are scaffolding proteins that provide the structural basis for the assembly of multiprotein complexes at the cytoplasmic surface of intercellular junctions. In addition, they provide a link between the integral membrane proteins and the filamentous cytoskeleton.
a) Macula adherens denote desmosomes that are the welded areas between the adjacent cells that have intracellular transmembrane linkers, thickening materials, disc-shaped intracellular thickening which is adjacent to each membrane and contains tonofibrils.
b) Zonula adherens denote terminal bars, namely, desmosomes which lack tonofibrils and in these junctions, the discoid thickenings are replaced by the bands of micro and intermediate filaments.
c) A gap junction can also be called a Nexus or Macula communicans. It is involved in intracellular adhesion and intracellular transport.
So, the correct answer is option C.

Additional Information: Gap junctions also known as nexus, allow the flow of ions, metabolites like amino acids, and other water-soluble molecules. They do not allow macromolecules such as proteins to pass through the channel because of its narrow diameter.

Note: The cardiac muscle cells contain three different kinds of intercellular junctions:
1)gap junctions 2) spot desmosomes 3) sheet desmosomes also known as fasciae adherents. These junctions are present in a definite portion in the plasma membrane which is the intercalated disk.