Ligands membrane-associated molecules

Fig. 3. Levels of complexity in receptor state and location. Receptors may be unbound, bound, or coupled with other membrane-associated molecules. Receptors and their ligands may be internalized and routed through intracellular compartments. Both receptors at the cell surface and receptors inside the cell may have signaling capabilities, although these capabilities are likely to be a function of the receptor state and location.

PTKs are monomeric in the active form, and consist of an extracellular binding domain, single membrane-associated a-helix and cytosolic domain with the kinase activity. Ligand binding induces dimerization and autophosphorylation that enables binding to adaptor molecules. These molecules connect the receptor to the signal transmitting biopolymers. 

Noncovalent interactions are central to many key biological functions. The self-assembly of the plasma and organelle membranes, association between receptors and ligands, and folding of RNA and protein molecules are all controlled by noncovalent interactions. Noncovalent forces in the design of proteins have proved useful in gaining insight into... 

FRAP is a powerful tool for investigating transmembrane proteins or proteins associated with the cell membrane. For instance, FRAP of molecules on the cell membrane can provide information about the molecules size, environment, and participation in intermolecular interactions, including ligand-driven associations... 

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