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macromolecular assembly
The term macromolecular assembly (MA) refers to massive chemical structures such as viruses and non-biologic nanoparticles, cellular organelles and membranes and ribosomes, etc. that are complex mixtures of polypeptide, polynucleotide, polysaccharide or other polymeric macromolecules. They are generally of more than one of these types, and the mixtures are defined spatially (i.e., with regard to their chemical shape), and with regard to their underlying chemical composition and structure. Macromolecules are found in living and nonliving things, and are composed of many hundreds or thousands of atoms held together by covalent bonds; they are often characterized by repeating units (i.e., they are polymers). Assemblies of these can likewise be biologic or non-biologic, though the MA term is more commonly applied in biology, and the term supramolecular assembly is more often applied in non-biologic contexts (e.g., in supramolecular chemistry and nanotechnology). MAs of macromolecules are held in their defined forms by non-covalent intermolecular interactions (rather than covalent bonds), and can be in either non-repeating structures (e.g., as in the ribosome (image) and cell membrane architectures), or in repeating linear, circular, spiral, or other patterns (e.g., as in actin filaments and the flagellar motor, image). The process by which MAs are formed has been termed molecular self-assembly, a term especially applied in non-biologic contexts. A wide variety of physical/biophysical, chemical/biochemical, and computational methods exist for the study of MA; given the scale (molecular dimensions) of MAs, efforts to elaborate their composition and structure and discern mechanisms underlying their functions are at the forefront of modern structure science.
== Roles ==
The complexes of macromolecules that are referred to as MAs occur ubiquitously in nature, where they are involved in the construction of viruses and all living cells. In addition, they play fundamental roles in all basic life processes (protein translation, cell division, vesicle trafficking, intra- and inter-cellular exchange of material between compartments, etc.). In each of these roles, complex mixtures of become organized in specific structural and spatial ways. While the individual macromolecules are held together by a combination of covalent bonds and ''intra''molecular non-covalent forces (i.e., associations between parts within each molecule, via charge-charge interactions, van der Waals forces, and dipole-dipole interactions such as hydrogen bonds), by definition MAs themselves are held together solely via the noncovalent forces, except now exerted ''between'' molecules (i.e., intermolecular interactions).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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