Cell Communication: Surface Receptors & Adhesion Molecules - Online Tutor, Practice Problems & Exam Prep

Cell communication is vital for immune responses, involving surface receptors and adhesion molecules. Surface receptors, which span the cytoplasmic membrane, bind specific ligands to trigger cellular responses. Adhesion molecules facilitate the binding of immune cells to endothelial cells, enabling their migration into infected tissues. This process is crucial for effective immunity, allowing immune cells to respond to infections by entering affected areas and delivering signaling molecules. Understanding these mechanisms enhances our knowledge of cellular immunity and the body's defense strategies against pathogens.

Cell Surface Receptors

This video, we're going to begin our lesson on cell communication by focusing on surface receptors and adhesion molecules. Cell surfaces contain many types of receptor proteins, as well as many types of adhesive molecules. These receptor proteins and adhesive molecules are important for communication during an infection. They allow cells of the immune system to signal an infection and to migrate to the infected location within the body. First, we're going to focus on cell surface receptors, and then later we'll focus on adhesive molecules. Cell surface receptors, or just surface receptors, are proteins on the cell surface. They specifically allow the cell to sense and respond to external signals or environmental signals. The surface receptor protein spans the entire cytoplasmic membrane, connecting the outside of the cell to the inside, allowing the cell to respond to external signals. Each specific surface receptor binds to a specific molecule.

Surface receptors do not respond to all molecules; they only respond to very specific molecules. We refer to these molecules as ligands. A ligand is a molecule that binds to a surface receptor. When a ligand binds to a surface receptor, it can elicit a response inside the cell, allowing the cell to respond to the external signal. Cells are capable of altering the number and types of surface receptors they have. This allows the cells to change their response rates and sensitivity to a certain ligand. Notice in the image below, we're showing you our map of the lesson on the scanning systems of innate immunity, which serve as security cameras. We're specifically focusing on cell communication and the surface receptors in this video. Notice that on the left-hand side, we're showing you a signaling cell that is creating some kind of signal. We can refer to this signal as the ligand in this case.

This signal or ligand can bind to these receptor proteins. The cell surface receptors are shown in purple, and this is the recipient cell. Only cells that have the specific cell receptor can respond to this specific ligand. The binding of the ligand to the cell surface receptor will trigger a cascade of events, causing one substance to lead to another, ultimately leading to some kind of cellular response allowing the cell to respond to external signals. This is how cell communication can occur and is very important for immunity. This concludes our brief introduction to the cell surface receptors that are important for cell communication. Later in our next lesson video, we'll talk more about the adhesion molecule. I'll see you all in our next video.

Which of the following is likely to be a response by a receptor protein to an approaching signal molecule?

• A. Recognize the receptor protein having the correct 3-D shape.
• B. Receptor protein binds to signal if having complementary shape.
• C. Once a signal binds to a receptor protein it induces a change in the receptor protein's shape.
• D. Change in the receptor protein's shape results in a cellular response to the signal.
• E. All of the above are correct.

Which of the following statements about cell surface receptors is incorrect?

• A. Cell surface receptors can span the entire plasma membrane connecting the exterior and interior cell environments.
• B. Once differentiated, cells cannot change the number or type of cell surface receptors that they possess.
• C. A cell has a wide range of surface receptors to allow it to respond to varying types of signals.
• D. The immune system uses ligands and cell surface receptors to provide immune support for infected tissues.

Adhesion Molecules

This video, we're going to talk about adhesion molecules and their role in cell communication. Adhesion molecules, as their name implies, are cell surface proteins involved in adhering or binding to other cells. This adhesion is very important because it allows immune system cells to bind to adhesion molecules of endothelial cells that line the blood vessels, which allows these immune system cells to enter into the tissues that are infected with microbes. These adhesion molecules can also be used by cells to attach to other cells and directly deliver signaling molecules to the cell that they are binding to.

If we take a look at our image down below on the left-hand side, notice that we're showing you our map of the lesson on the scanning systems of innate immunity, which serve as security cameras to detect signs of microbes. We're focusing specifically on cell communication and adhesion molecules here in this video. Notice here we're showing you adhesion molecules and how they are important in cellular immunity. Notice that here we're showing you our blood vessels. If a site is going to be infected in the tissues, then what can happen is the cells that line the blood vessels, the endothelial cells, can create adhesion molecules.

Notice that these adhesion molecules that are created by these particular cells lining the blood vessels allow for cells of the immune system to bind, and what you can see here is a binding event where adhesion molecules on the immune cells can bind to adhesion molecules on the endothelial cells lining the blood vessels. This binding event can slow down these immune system cells and allow these immune system cells to migrate from the blood into the tissues. That migration of these immune system cells into the tissues allows them to attack and generate immune responses to the microbial infection or the bacterial infection here in this case. Adhesion molecules are very important for cell communication and allowing cells to migrate to an area of infection.

This here concludes our brief lesson on adhesion molecules and their role in cell communication. We will be able to apply these concepts as we move forward. Also, we'll talk about cytokines in upcoming sessions. So I'll see you all in our next video.

Why are adhesion molecules considered a form of cell communication in immune responses?

• A. Adhesion molecules allow immune cells to attach to infected cells & signal immune responses.
• B. Adhesion molecules allow immune cells to attach to endothelial cells & trigger immune cell entry into tissues.
• C. Adhesion molecules act as channels that allow signals to travel between two neighboring cells.
• D. Adhesion molecules are signals sent from immune cells to infected cells to trigger apoptosis.
• E. A and B.
• F. C and D.
• G. All of the above.

If the endothelial cells of the blood vessels in the body did not possess adhesion molecules, which of the following would occur?

a) The immune cells which respond to infection or injury would not be able to leave the blood stream.

b) The immune cells would not be able to detect where the infection is in the body.

c) The immune cells would not be able to phagocytose the infecting microbes and damaged tissue.

d) The blood vessels would adhere to the immune cells allowing them entry to infected regions of the body.

• A. The immune cells which respond to infection or injury would not be able to leave the blood stream.
• B. The immune cells would not be able to detect where the infection is in the body.
• C. The immune cells would not be able to phagocytose the infecting microbes and damaged tissue.
• D. The blood vessels would adhere to the immune cells allowing them entry to infected regions of the body.

Here’s what students ask on this topic:

What are cell surface receptors and how do they function in cell communication?

Cell surface receptors are proteins located on the cell membrane that play a crucial role in cell communication. These receptors span the entire cytoplasmic membrane, connecting the outside of the cell to the inside. They function by binding to specific molecules known as ligands. When a ligand binds to its corresponding receptor, it triggers a cascade of intracellular events, leading to a cellular response. This process allows the cell to sense and respond to external signals, which is vital for various physiological processes, including immune responses. Cells can also alter the number and types of surface receptors they express, thereby modulating their sensitivity and response to specific ligands.

What role do adhesion molecules play in the immune system?

Adhesion molecules are cell surface proteins that facilitate the binding of immune cells to other cells, such as endothelial cells lining blood vessels. This binding is essential for immune responses, as it allows immune cells to migrate from the bloodstream into infected tissues. The adhesion molecules on endothelial cells bind to those on immune cells, slowing them down and enabling their migration into tissues. This process is crucial for the immune system to effectively respond to infections, allowing immune cells to reach and attack pathogens in the affected areas. Additionally, adhesion molecules can help deliver signaling molecules directly to target cells, enhancing immune communication.

How do ligands and surface receptors interact to trigger a cellular response?

Ligands are specific molecules that bind to cell surface receptors, initiating a cellular response. Each surface receptor is designed to bind to a specific ligand. When a ligand binds to its corresponding receptor, it causes a conformational change in the receptor protein. This change triggers a series of intracellular signaling pathways, often involving secondary messengers and protein kinases. These pathways lead to various cellular responses, such as gene expression, enzyme activation, or changes in cell behavior. This interaction is fundamental for cells to respond to external signals, enabling processes like immune responses, cell growth, and differentiation.

Why is the ability of cells to alter the number and types of surface receptors important?

The ability of cells to alter the number and types of surface receptors is crucial for modulating their sensitivity and response to specific ligands. This adaptability allows cells to fine-tune their responses to changing environmental conditions and external signals. For example, during an immune response, cells may increase the expression of certain receptors to enhance their ability to detect and respond to pathogens. Conversely, cells can downregulate receptors to reduce sensitivity and prevent overactivation. This dynamic regulation ensures that cells can effectively respond to various stimuli, maintaining homeostasis and proper physiological function.

How do adhesion molecules facilitate the migration of immune cells to infected tissues?

Adhesion molecules facilitate the migration of immune cells to infected tissues by enabling these cells to bind to endothelial cells lining blood vessels. When an infection occurs, endothelial cells express specific adhesion molecules. Immune cells, such as leukocytes, have complementary adhesion molecules that bind to those on the endothelial cells. This binding slows down the immune cells, allowing them to adhere to the blood vessel walls. Subsequently, the immune cells can migrate through the vessel walls into the surrounding infected tissues. This process, known as extravasation, is essential for immune cells to reach and combat pathogens effectively.