Cell Communication: Surface Receptors & Adhesion Molecules: Videos & Practice Problems

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.

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.

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.

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.

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.