DNA structure

The structure of DNA shows a variety of forms, both double-stranded and single-stranded. The mechanical properties of DNA, which are directly related to its structure, are a significant problem for cells. Every process which binds or reads DNA is able to use or modify the mechanical properties of DNA for purposes of recognition, packaging and modification. The extreme length (a chromosome may contain a 10 cm long DNA strand), relative rigidity and helical structure of DNA has led to the evolution of histones and of enzymes such as topoisomerases and helicases to manage a cell's DNA. The properties of DNA are closely related to its molecular structure and sequence, particularly the weakness of the hydrogen bonds and electronic interactions that hold strands of DNA together compared to the strength of the bonds within each strand.

Experimental techniques which can directly measure the mechanical properties of DNA are relatively new, and high-resolution visualization in solution is often difficult. Nevertheless, scientists have uncovered large amount of data on the mechanical properties of this polymer, and the implications of DNA's mechanical properties on cellular processes is a topic of active current research. 

The DNA found in many cells can be macroscopic in length - a few centimetres long for each human chromosome. Consequently, cells must compact or "package" DNA to carry it within them. In eukaryotes this is carried by spool-like proteins known as histones, around which DNA winds. It is the further compaction of this DNA-protein complex which produces the well known mitotic eukaryotic chromosomes.

What is biophysics?

 
  Biophysics is a branch of the sciences which applies chemistry and physics to the study of living organisms. For example, a biophysicist might explore cell signaling, in which cells transmit chemicals to each other to stimulate various responses. This field is extremely varied, with a number of applications, and new topics in biophysics are constantly being developed and discussed by researchers and other professionals in the field.
Biophysics is an interdisciplinary field which applies techniques from the physical sciences to understanding biological structure and function at the molecular level. In simpler terms we use a range of scientific techniques to try to understand what macromolecules like DNA, proteins, fats and sugars look like, and how they interact to form the biological systems around us. Plants, animals and even seemingly simple organisms like bacteria and archae consist of complex biological networks of chemical signals and molecular interactions, which enable them to do such things as move, respire or reproduce. Biophysics is a varied field which draws on biology, physics, chemistry, mathematics, engineering, genetics, physiology and medicine, all with the aim to understand these systems using experiments or theoretical and computational modeling. It is also a young science and is still rapidly developing - bionanotechnology and biosensors are just some of the latest fields to emerge in the last few years.