Chapter 3
Question 23-Compare the structure and function of tight junctions, desmosomes, and gap junctions

1)In tight junctions, there are plasma membranes of adjacent cells that fuse together. In the membranes are a series of integral proteins molecules. They form an impermeable junction that makes a circle around the cell. These tight junctions help prevent molecules from passing through the spaces between other cells nearby. For example tight junctions between epithelial cells lining the digestive tract keep digestive enzymes and microorganisms in the intestine, and leaking into the blood.
2)Desmosomes act as anchoring junctions. There are mechanical couplings all along the other cells to keep them from separating. They have a thickening plaque on the cytoplasmic face of each plasma membrane. The adjacent cells are held together by zipper like linker proteins filaments that extend from the plaque and form the zipper in the intercellular space. There are thicker protein filaments that extend across the cell to the other side of it. Desmosomes are also contribute to a continuous internal network of strong "guy wires" also, they bond cells near themselves together. They are subject to pulling forces, like in the skin and heart muscle
3)Gap junctions is a junction that communicates, and lets chemical substances to go between cells near by. The cells that are connected by hollow cylinders are called connexons and are composed of transmembrane protiens, that are very close to the adjacent plasma membranes. Gap junctions are in electrically excitable tissues such as the heart and smooth muscle where ions move cell to cell, to sync the electrical activity and contraction