Final answer:
Membrane proteins have major functions such as transport, enzymatic activity, cell surface receptor, cell-cell recognition and adhesion, and attachment to the cytoskeleton and extracellular matrix.
Step-by-step explanation:
The major functions of membrane proteins include:
Transport: Membrane proteins act as transporters, facilitating the movement of molecules across the cell membrane. This can include both passive transporters, which utilize facilitated diffusion, and active transporters, which use energy to move molecules against their concentration gradient.
Enzymatic Activity: Some membrane proteins function as enzymes, catalyzing crucial reactions within the cell. Examples include the electron transport complexes in mitochondria and the F1 ATP synthase enzyme.
Cell Surface Receptor (Signal Transduction): Membrane proteins can act as receptors, receiving signals from external molecules such as hormones or neurotransmitters, and initiating intracellular signaling pathways in response.
Cell-Surface (Cell-Cell) Recognition and Cell-to-Cell Adhesion: Membrane proteins play a role in cell recognition, allowing cells to recognize and bind to each other. They are involved in important processes such as tissue and organ formation during development.
Attachment to Cytoskeleton and ECM: Some membrane proteins anchor the cell to the cytoskeleton or extracellular matrix (ECM), maintaining cell structure and providing stability.