Cell Junctions - Online Tutor, Practice Problems & Exam Prep

Cell junctions are crucial for communication and structural integrity between neighboring eukaryotic cells. The four main types include tight junctions, which create leak-proof barriers; anchoring junctions (desmosomes), which connect cells using intermediate filaments; gap junctions, which form channels for nutrient exchange; and plasmodesmata, the plant equivalent of gap junctions. Understanding these junctions is essential for grasping cellular interactions and tissue organization in both animal and plant cells.

Cell Junctions

In this video, we're going to begin our introduction to cell junctions. Neighboring cells of eukaryotic organisms are able to directly interact with one another using cell junctions. Now, really, there are four main types of cell junctions that you all should know that link adjacent cells together. Notice below here, we're showing you this table of the four types of cell junctions that you all should know. You can see the junction type on the left-hand side and then the description of each of the junctions on the right-hand side. Below, we have some images of each of these four junctions.

The very first junction that you all should know is the tight junctions, which are membrane proteins that link cells together in a tight fashion to create leak-proof barriers. When you drink a glass of lemonade, the lemonade does not leak between your cells and end up on the floor, thanks to tight junctions, which create leak-proof barriers. If we take a look at our image below on the left-hand side, notice that we're showing you an example of a tight junction. The yellow barriers that you see here represent the plasma membrane of two different cells. The gray circles you see represent proteins that are tightly linking these two cells together to create a leak-proof barrier. This way, liquids cannot seep in between the cells because they're so tightly held together.

The second type of junctions you all should know are the anchoring junctions, or sometimes referred to as desmosomes. The anchoring junctions are intermediate filaments that anchor neighboring cells together using complex protein structures. Below, you can see that we're showing you an image of anchoring junctions, also known as desmosomes. You can see that they use these complex protein structures made of intermediate filaments to link two neighboring cells together. Anchoring junctions may not be leak-proof, allowing things to seep between the cells, unlike tight junctions, which are so tightly held together that they are leak-proof.

Moving on, the third type of cell junction that you all should know are the gap junctions. These are protein channels that create a gap between two cells. They connect the cytoplasm of two animal cells. When we take a look below, notice that we're showing you an example of gap junctions. These proteins create channels between the cytoplasm of two neighboring cells. The yellow barriers that you see here represent the cell membranes of two neighboring cells. The protein channels you see here create a pore between the two membranes so that they can exchange nutrients and other substances.

The first three junctions we talked about—tight, anchoring, and gap junctions—are all only found in animal cells. The question then arises about plant cells that have cell walls. How do they create cell junctions? This fourth and last junction is all about the plasmodesmata. Plasmodesmata are gaps in the cell walls that connect the cytoplasm of two neighboring plant cells. These junctions are specifically found in plant cells, whereas the other three are found in animal cells. If we take a look at our image below of plasmodesmata, notice that we're showing you three neighboring plant cells, and they have gaps in their cell walls that allow these plant cells to exchange nutrients with one another, connecting the cytoplasm of the neighboring plant cells. That is what plasmodesmata allow for.

This concludes our introduction to cell junctions, and we'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.

Which of the following are only in plant cells and not in animal cells?

• A. Gap junctions.
• B. Desmosomes.
• C. Plasmodesmata.
• D. Tight junctions.

Ions can travel directly from the cytoplasm of one animal cell to the cytoplasm of an adjacent cell through:

• A. Gap junctions.
• B. Desmosomes.
• C. Tight junctions.
• D. Intermediate filaments.
• E. Plasmodesmata.
• F. Actin filaments.

Here’s what students ask on this topic:

What are the main types of cell junctions in eukaryotic cells?

The main types of cell junctions in eukaryotic cells are tight junctions, anchoring junctions (desmosomes), gap junctions, and plasmodesmata. Tight junctions create leak-proof barriers between cells, preventing substances from passing through. Anchoring junctions, or desmosomes, use intermediate filaments to connect cells, providing structural support. Gap junctions form protein channels that allow the exchange of nutrients and other molecules between the cytoplasm of adjacent animal cells. Plasmodesmata are found in plant cells and serve a similar function to gap junctions, creating channels through the cell walls to connect the cytoplasm of neighboring plant cells.

How do tight junctions function in animal cells?

Tight junctions function in animal cells by creating leak-proof barriers between adjacent cells. They are composed of membrane proteins that tightly link the plasma membranes of neighboring cells. This tight connection prevents the passage of substances between the cells, ensuring that materials must pass through the cells rather than between them. This is crucial for maintaining the integrity of tissues and preventing the leakage of fluids, such as in the lining of the intestines where tight junctions prevent digestive enzymes and other substances from seeping between cells.

What is the role of desmosomes in cell junctions?

Desmosomes, also known as anchoring junctions, play a crucial role in providing structural support and stability to tissues. They connect adjacent cells using complex protein structures made of intermediate filaments. These filaments anchor the cells together, allowing them to withstand mechanical stress and maintain tissue integrity. Desmosomes are particularly important in tissues that experience significant mechanical stress, such as the skin and heart muscle, where they help prevent cells from being pulled apart.

How do gap junctions facilitate communication between cells?

Gap junctions facilitate communication between cells by forming protein channels that connect the cytoplasm of adjacent cells. These channels allow the direct exchange of ions, nutrients, and other small molecules, enabling cells to coordinate their activities. This is essential for processes such as electrical signaling in cardiac and smooth muscle tissues, where gap junctions allow for the rapid and synchronized contraction of cells. By enabling the transfer of signaling molecules, gap junctions play a key role in maintaining tissue homeostasis and function.

What are plasmodesmata and how do they function in plant cells?

Plasmodesmata are channels that traverse the cell walls of plant cells, allowing for the direct exchange of substances between the cytoplasm of adjacent cells. These channels are lined with plasma membrane and contain a thin strand of cytoplasm, facilitating the movement of ions, nutrients, and signaling molecules. Plasmodesmata are crucial for maintaining the physiological and developmental coordination of plant tissues, enabling cells to communicate and share resources efficiently. They are the plant equivalent of gap junctions found in animal cells.