Understanding Types of Cellular Junctions - AP Biology

Gap junctions are cellular junctions that attach two or more cells together but also allow the exchange of products through an opening. Tight junctions, desmosomes, and hemidesmosomes do not allow direct communication among cells.

Within the digestive tract, it is important for nutrients and toxins to remain contained within the organs to allow for proper absorption. Furthermore, the acidity and basicity of various regions of the digestive tract must be kept partitioned from the rest of the body. Tight junctions are found between most cells of the digestive tract. This type of cell junction prevents movement of material between cells, requiring it to actually move into cells via diffusion or active transport in order to pass through tissue.

Gap junctions are intercellular junctions that connect the cytoplasm of adjacent cells and are particularly important for signaling. Desmosomes are structures specialized for cell-to-cell adhesion and force transmission. Plasmodesmata are transport and communication channels in plant cells, analogous to gap junctions.

Gap junctions are formed by connexons—rings of proteins that spans the membranes of two adjacent cells. The ring surrounds a pore that allows ions, among other substances, to pass between the cells uninterrupted. The result is a quick transmission of the electrochemical signal for cardiac muscle cell contraction, so that the cells contract essentially together. Gap junctions can also be found in numerous other tissue types, but not in skeletal muscle.

Gap junctions allow the flow of water and ions. They are seen in the heart muscle cells, to allow quick electrical conduction from one cell to another, which is observed as a wavelike contraction of the heart. Tight junctions are networks of spot attachments that are impermeable to fluids. Desmosomes are random, spot attachments that are responsible for cell-cell adhesion.

In animal cells, gap junctions allow materials such as ions to flow directly from the cytoplasm of one cell to that of the next. They can be thought of as channels, or "bridges" between cells. Gap junctions are common in the muscle tissue of animals' hearts, for example, as they allow ions to pass rapidly from cell to cell to coordinate cardiac muscle contraction. Plasmodesmata connect plant cells to one another in the same way, and they enable rapid transport and communication between adjacent cells.

Desmosomes are another type of cell junction found in animal cells, though they "rivet" cells together instead of forming a channel; they most frequently prevent epithelial and some muscle cells from shearing apart.

Tight junctions form an even tighter seal than those formed by desmosomes. They form a bond that is almost completely impermeable to fluid. Tight junctions join cells together, and also help regulate the movement of molecules and ions.

Vacuoles are not a type of cell junction at all. These organelles are found in plant cells and are used for storage, digestion, and the filling of space.

Tight junctions commonly line organs such as the urinary bladder, as they prevent unwanted fluid from leaking into or out of these organs. They are most notable for their barrier function: they are almost completely impermeable to fluid.

Though desmosomes also join cells together, they are more commonly found connecting cells that are subject to mechanical stress, such as muscles or the outer layer of skin. They are comparable to a button or a rivet, and do not connect cells as tightly to one another as tight junctions do. Gap junctions are essentially channels between cells that enable the rapid transport of ions and other solutes between the cytoplasm of neighboring cells; they would not help keep urine within the urinary bladder. Plasmodesmata are only found in plants (they are analogous to gap junctions) and would therefore have no business forming a human bladder.

Cardiac myocytes (muscle cells) need to be able to contract in unison in order to ensure proper pumping of blood. This is accomplished by specialized junctions called gap junctions that allow cells to communicate with one another very quickly. These junctions join the cytoplasms of adjacent cells, allowing ions to flow between them. When one cardiac cell is depolarized, the gap junctions found in intercalated discs allow the depolarization to jump from cell to cell.

Plasmodesmata are structurally analogous to gap junctions, but are located in plant cells.

Gap junctions form pores connecting neighboring cells and allowing the mixture of cytoplasm and small solutes including ions. Desmosomes are specialized for cell-cell adhesion, and hemidesmosomes are specialized for cell-extracellular matrix adhesion. Tight junctions (occluding junctions) form a seal across a layer of cells and is virtually impermeable.

Gap junctions are protein channels that span the intercellular space that connect two cells. They allow cytoplasmic exchange in animal cells. The diameter of gap junctions limits what is able to travel though them from one cell to another. Ions, amino acids, and small molecules can flow through gap junctions; however, proteins, polysaccharides, and nucleic acids cannot. Gap junctions allow the transfer of small molecules to direct communication and cellular activities.

The answer to this question is facilitated diffusion.

Facilitated diffusion involves the movement down a concentration across a plasma membrane without ATP. Bulk flow is a completely different process and active transport is the movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy. Active transport needs an input of energy, unlike facilitated diffusion. Osmosis is the simple diffusion of water.

Within the digestive tract, it is important for nutrients and toxins to remain contained within the organs to allow for proper absorption. Furthermore, the acidity and basicity of various regions of the digestive tract must be kept partitioned from the rest of the body. Tight junctions are found between most cells of the digestive tract. This type of cell junction prevents movement of material between cells, requiring it to actually move into cells via diffusion or active transport in order to pass through tissue.

Gap junctions are intercellular junctions that connect the cytoplasm of adjacent cells and are particularly important for signaling. Desmosomes are structures specialized for cell-to-cell adhesion and force transmission. Plasmodesmata are transport and communication channels in plant cells, analogous to gap junctions.

Gap junctions are formed by connexons—rings of proteins that spans the membranes of two adjacent cells. The ring surrounds a pore that allows ions, among other substances, to pass between the cells uninterrupted. The result is a quick transmission of the electrochemical signal for cardiac muscle cell contraction, so that the cells contract essentially together. Gap junctions can also be found in numerous other tissue types, but not in skeletal muscle.

Gap junctions allow the flow of water and ions. They are seen in the heart muscle cells, to allow quick electrical conduction from one cell to another, which is observed as a wavelike contraction of the heart. Tight junctions are networks of spot attachments that are impermeable to fluids. Desmosomes are random, spot attachments that are responsible for cell-cell adhesion.

In animal cells, gap junctions allow materials such as ions to flow directly from the cytoplasm of one cell to that of the next. They can be thought of as channels, or "bridges" between cells. Gap junctions are common in the muscle tissue of animals' hearts, for example, as they allow ions to pass rapidly from cell to cell to coordinate cardiac muscle contraction. Plasmodesmata connect plant cells to one another in the same way, and they enable rapid transport and communication between adjacent cells.

Desmosomes are another type of cell junction found in animal cells, though they "rivet" cells together instead of forming a channel; they most frequently prevent epithelial and some muscle cells from shearing apart.

Tight junctions form an even tighter seal than those formed by desmosomes. They form a bond that is almost completely impermeable to fluid. Tight junctions join cells together, and also help regulate the movement of molecules and ions.

Vacuoles are not a type of cell junction at all. These organelles are found in plant cells and are used for storage, digestion, and the filling of space.

Tight junctions commonly line organs such as the urinary bladder, as they prevent unwanted fluid from leaking into or out of these organs. They are most notable for their barrier function: they are almost completely impermeable to fluid.

Though desmosomes also join cells together, they are more commonly found connecting cells that are subject to mechanical stress, such as muscles or the outer layer of skin. They are comparable to a button or a rivet, and do not connect cells as tightly to one another as tight junctions do. Gap junctions are essentially channels between cells that enable the rapid transport of ions and other solutes between the cytoplasm of neighboring cells; they would not help keep urine within the urinary bladder. Plasmodesmata are only found in plants (they are analogous to gap junctions) and would therefore have no business forming a human bladder.

Cardiac myocytes (muscle cells) need to be able to contract in unison in order to ensure proper pumping of blood. This is accomplished by specialized junctions called gap junctions that allow cells to communicate with one another very quickly. These junctions join the cytoplasms of adjacent cells, allowing ions to flow between them. When one cardiac cell is depolarized, the gap junctions found in intercalated discs allow the depolarization to jump from cell to cell.

Plasmodesmata are structurally analogous to gap junctions, but are located in plant cells.

Gap junctions form pores connecting neighboring cells and allowing the mixture of cytoplasm and small solutes including ions. Desmosomes are specialized for cell-cell adhesion, and hemidesmosomes are specialized for cell-extracellular matrix adhesion. Tight junctions (occluding junctions) form a seal across a layer of cells and is virtually impermeable.

Gap junctions are protein channels that span the intercellular space that connect two cells. They allow cytoplasmic exchange in animal cells. The diameter of gap junctions limits what is able to travel though them from one cell to another. Ions, amino acids, and small molecules can flow through gap junctions; however, proteins, polysaccharides, and nucleic acids cannot. Gap junctions allow the transfer of small molecules to direct communication and cellular activities.

Plasmodesmata are the plant structures that are analogous to gap junctions in animal cells. Plasmodesmata are protein channels between the cell walls of plant cells. They facilitate communication and the transport of solutes and small proteins between plant cells.