ABSTRACT
Polymer translocation is one of the most fundamental macromolecular processes in life. This ubiquitous phenomenon deals with how electrically charged polymer molecules, such as polynucleotides and proteins, move from one region of space to another in crowded environments. Examples of biological phenomena for which polymer translocation is a crucial fundamental step include passage of mRNA through nuclear pore complexes, injection of DNA from a virus head into a host cell, gene swapping through pili, and protein translocation across biological membranes through channels (Lodish et al. 2007, Alberts et al. 2008). In addition, primarily due to societal and technological demands on DNA sequencing, there has recently been a tremendous effort to monitor and control the translocation of single macromolecules through a single pore made of proteins or synthetic solid-state materials. Although these apparently diverse phenomena emerge from different specific chemical details that are unique to each of these phenomena, we seek to identify the most common universal features behind these phenomena. The chemical details indeed decorate the basic universal feature of the passage of long macromolecules differently and impart specific directions and targets. We will first attempt to identify the common universal aspects of translocation and then to explore ways of incorporating the specific details relevant to different contexts. After illustrating the richness of the phenomenon with a few examples, we will offer an operating definition of the process and introduce the main concept, namely the entropic barrier idea (Muthukumar 2007), behind the polymer translocation. This will be followed by a brief outline of the various significant components, which need to be put together for a molecular understanding of the polymer translocation phenomenon.
