Final answer:
Cell-surface receptors are integral proteins with external ligand-binding, membrane-spanning, and intracellular domains. They are key for signal transduction, responding to various ligands, and can be exploited by pathogens to invade cells.
Step-by-step explanation:
Cell-surface receptors, also known as transmembrane receptors, are integral proteins located on the cell surface that play a crucial role in signal transduction. These receptors are composed of three main components:
- An external ligand-binding domain or extracellular domain that binds to specific signaling molecules such as hormones, neurotransmitters, growth factors, or mating factors.
- A hydrophobic membrane-spanning region that anchors the receptor within the cell's plasma membrane.
- An intracellular domain that communicates the signal to the interior of the cell, often triggering a cascade of cellular responses.
There are different types of cell-surface receptors, such as enzyme-linked receptors, ion channel-linked receptors, and G-protein-linked receptors. Each type is specialized in its function and responds to different ligands. Enzyme-linked receptors have intracellular domains associated with membrane-bound enzymes, whereas G-protein-linked receptors activate G-proteins to transmit signals internally.
Lastly, viruses and pathogens can exploit these receptors to invade cells by mimicking the ligands that they are designed to bind, with examples including HIV and hepatitis viruses targeting specific cell types.