The Cell Junctions allowing exchange of cytoplasmic molecules between two cells are called:
A. Gap Junctions
B. Tight Junctions
C. Anchoring Junctions
D. Focal Junctions
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Answer is A. Gap Junctions.
Gap Junctions are a type of intercellular junction comprising a narrowed portion (about 3 nm) of the intercellular space, that contains channels or pores (2 nm) composed of hexagonal arrays of membrane spanning proteins around a central lumen (connexon) through which pass ions and small molecules such as most sugars, amino acids, nucleotides, vitamins, hormones and cyclic AMP.
Gap junctions were so named because of the "gap" shown to be present at these special junctions between two cells. One gap junction is composed of two connexons (or hemichannels) which connect across the intercellular space. It directly connects the cytoplasm of two cells, which allows various molecules and ions to pass freely between cells.
To come to a definite conclusion about this answer, let us review the different types of cell connections. There are 3 major forms of direct cell connections.
A. Gap Junctions
B. Tight Junctions
C. Anchoring Junctions
D. Focal Junctions
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Answer is A. Gap Junctions.
Gap Junctions are a type of intercellular junction comprising a narrowed portion (about 3 nm) of the intercellular space, that contains channels or pores (2 nm) composed of hexagonal arrays of membrane spanning proteins around a central lumen (connexon) through which pass ions and small molecules such as most sugars, amino acids, nucleotides, vitamins, hormones and cyclic AMP.
Gap junctions were so named because of the "gap" shown to be present at these special junctions between two cells. One gap junction is composed of two connexons (or hemichannels) which connect across the intercellular space. It directly connects the cytoplasm of two cells, which allows various molecules and ions to pass freely between cells.
To come to a definite conclusion about this answer, let us review the different types of cell connections. There are 3 major forms of direct cell connections.
- Desmosomes: Small 'spot-welds' that hold adjacent cells together. Fibres on the outer surface of each desmosome interlock with each other. Internally, they are anchored by fibres of the cytoskeleton.
- Adjacent Skin Cells are typical examples of desmosome.
- Gap Junctions: Formed when membrane channels of adjacent plasma membranes adhere to each other. These serve two effects:
- Form gaps or tunnels that join cytoplasm of two cells.
- Fuse the two plasma membranes into a single structure
- Examples include Myocardial Fibres, Central Nervous System
- Tight Junctions: Occur in cells that are joined by collars of tightly fused membranes. Molecules cannot penetrate or spread through cracks in between cells.
- Example includes Lining of the intestine (the only way molecules can get past is through controlled channels or carrier molecules in plasma membrane).
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