What kinds of cell junctions would you expect to find, and why, in the following situations?

a. in the digestive system, where material must pass through cells, and not go through the extracellular material, to get from the intestine to the blood vessels.
b. in a small animal, where a chemical signal passes rapidly though cells to go from the head to the tail.
c. in the lining of the intestine, where cells in the lining are constantly jostled by the churning of the underlying muscle.

1. Tight junction = Prevents leakage to material into the extracellular space.

2. Gap junction=Gap junctions connect the neighboring cells to allow the diffusion of ions and small molecules from one cell to the another.

3. Desmosomes: Desmosomes impart stability to cells and prevent them to separate under tension.

Explanation:

Tight junctions form strands of transmembrane proteins that fuse the outer surfaces of neighboring plasma membranes and thereby prevent the passage of materials between the neighboring cells.

Connexins, the proteins of gap junctions form channels (connexons) to connect the adjacent cells. The plasma membranes of neighboring cells are separated from each other by a very narrow gap. Connexons allow the movement of ions and small molecules from one cell to the next.

The plaques of desmosomes are attached to the intermediate filaments of the cytoskeleton. The intermediate filaments from the desmosome on the one side of the cell extend out across to the desmosomes on the opposite side of the cell to make the cells stable under pressure or tension. This pattern does not allow the cells to separate from each other when exposed to tension like churning.

the right side of the picture going down is:

polymerase

protein

transport vesicle

modified protein

the left side of the picture going down is:

dna helix

single-stranded rna

endoplasmic reticulum

ribosome

golgi apparatus

protein released from vesicle

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