What is the Difference Between Tight Junction and Gap Junction

The main difference between tight junction and gap junction is that tight junction regulates the movement of water and solutes between epithelial layers whereas gap junction allows the direct chemical communication between adjacent cytoplasms. 

Tight junction and gap junction are two types of cell junctions that occur between the cells of vertebrates. Furthermore, the plasma membranes involved in a tight junction are very tightly pressed against each other and contain different proteins while a gap junction contains channels from one to the other cytoplasm and membrane proteins surround each pore.

Key Areas Covered

1. What is a Tight Junction
     – Definition, Structure, Function
2. What is a Gap Junction
     – Definition, Structure, Function
3. What are the Similarities Between Tight Junction and Gap Junction
     – Outline of Common Features
4. What is the Difference Between Tight Junction and Gap Junction
     – Comparison of Key Differences

Key Terms

Cell Junction, Claudins, Communication, Connexins, Electrical Synapse, Gap Junction, Tight Junction

What is a Tight Junction

Tight junction is a multiprotein junctional complex responsible for preventing the leakage of the transporting water and solutes, sealing the paracellular pathway. That means; the main function of a tight junction is to create a watertight seal between two adjacent cells. Also, tight junctions form selective pores for the transport of molecules including ions, small cations, and water. Invertebrates contain a type of cell junctions called septate junctions, which resemble tight junctions in vertebrates.

Figure 1: Tight Junction

Furthermore, proteins called claudins are mainly responsible for the tight holding of the two plasma membranes together. These proteins are arranged into strands, forming a branching network. Therefore, a large number of strands can make a tight seal.

What is a Gap Junction

A gap junction is a type of intercellular connection that directly connects the cytoplasm of two cells. Therefore, gap junctions form regulated gates between cells. They allow the movement of various molecules between the two cells including ions. Also, they allow passing electric impulses between cells. Therefore, gap junctions serve as electrical synapse although most nerve tissue of vertebrates does not contain gap junctions in the synapses. However, gap junctions serve as electrical synapses in the nerves of the dental pulp. Besides, gap junctions play a key role in cardiac muscles by spreading the electrical signals between heart muscle cells. Especially, these junctions resemble the plasmodesmata in plants.

Figure 2: Gap Junction

Moreover, a set of six membrane proteins called connexins are responsible for the formation of an elongated, doughnut-like structure called a connexon. The alignment of two connexons of adjacent cells results in the formation of a cytoplasmic channel.

Similarities Between Tight Junction and Gap Junction

• Tight junction and gap junction are two types of cell junctions that occur between adjacent cells in vertebrates.
• Both plasma membrane and various proteins are involved in the formation of these cell junctions.
• Also, both their main function is to hold animal cells together, combining with cell adhesion molecules and extracellular matrix.

Difference Between Tight Junction and Gap Junction

Definition

Tight junction refers to a specialized connection of two adjacent animal cell membranes, such that, space usually lying between them is absent while a gap junction refers to a linkage of two adjacent cells consisting of a system of channels extending across a gap from one cell to the other, allowing the passage. This is the main difference between tight junction and gap junction.

Other Names

Other names for tight junctions are occluding junctions and zonulae occludentes while the other names for gap junctions are nexus and macula communicans.

Occurrence

Another difference between tight junction and gap junction is that tight junctions occur in the epithelia of vertebrates while gap junctions occur in all types of tissues, except in fully-developed skeletal muscles and mobile cells types.

Structure

Moreover, tight junctions contain plasma membranes, which are very tightly pressed against each other due to bound proteins while gap junctions consist of cytoplasmic channels from one to the other cytoplasm, surrounding with membrane proteins. Hence, this is one other difference between tight junction and gap junction.

Type of Proteins

Another difference between tight junction and gap junction is the type of proteins. Tight junctions contain proteins called claudins while gap junctions contain proteins called connexins.

Function

Additionally, tight junctions regulate the movement of water and solutes between epithelial layers while gap junction allows the direct chemical communication between adjacent cytoplasm. Thus, the function is a difference between tight junction and gap junction.

Other Functions

Furthermore, tight junctions prevent the leakage of extracellular fluid across the epithelial cell layer while gap junctions allow the movement of ions, sugars, amino acids, and other small molecules between cells.

Conclusion

Tight junction is a type of cell junction found between the cells of vertebrates. It contains very tightly pressed plasma membranes of two cells. The main function of tight junction is to regulate the movement of water and solutes, preventing the leakage of the extracellular fluid across the epithelial cell layer. In comparison, gap junction is another type of cell junction in vertebrates, containing channels connecting the adjacent cytoplasm. Gap junctions facilitate cell to cell communication. Therefore, the main difference between tight junction and gap junction is their structure and function.

References:

1. “Cell-Cell Junctions.” Khan Academy, Khan Academy, Available Here

image courtesy:

1. “Cellular tight junction-en” By Mariana Ruiz LadyofHats – Image renamed from File:Cellular tight junction.svg (Public Domain) via Commons Wikimedia  
2. “Gap cell junction-en” By Mariana Ruiz LadyofHats – Made with Adobe Illustrator. Image renamed from File:Gap cell junction.svg (Public Domain) via Commons Wikimedia