Macromolecular assembly

Structure of nucleoprotein MA: The 50S ribosomal subunit from H. marismortui X-ray crystallographic model of 29 of the 33 native components, from the laboratory of Thomas Steitz. Of the 31 component proteins, 27 are shown (blue), along with its 2 RNA strands (orange/yellow).[1] Scale: assembly is approx. 24 nm across.[2]

In molecular biology, 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.

A eukaryotic ribosome, which catalytically translate the information content contained in mRNA molecules into proteins. The animation presents the elongation and membrane targeting stages of eukaryotic translation, showing the mRNA as a black arc, the ribosome subunits in green and yellow, tRNAs in dark blue, proteins such as elongation and other factors involved in light blue, the growing polypeptide chain as a black thread growing vertically from the curve of the mRNA. At end of the animation, the polypeptide produced is extruded through a light blue SecY pore[3] into the gray interior of the ER.
  1. ^ Ban N, Nissen P, Hansen J, Moore PB, Steitz TA (August 2000). "The complete atomic structure of the large ribosomal subunit at 2.4 A resolution". Science. 289 (5481): 905–920. Bibcode:2000Sci...289..905B. CiteSeerX 10.1.1.58.2271. doi:10.1126/science.289.5481.905. PMID 10937989.
  2. ^ McClure W. "50S Ribosome Subunit". Archived from the original on 2005-11-24. Retrieved 2019-10-09.
  3. ^ Osborne AR, Rapoport TA, van den Berg B (2005). "Protein translocation by the Sec61/SecY channel". Annual Review of Cell and Developmental Biology. 21: 529–550. doi:10.1146/annurev.cellbio.21.012704.133214. PMID 16212506.