DNA’s Double Stranded Stretch
What happens to DNA strands when stretched to the breaking point?
Theoretical physicists like to play with very unconventional toys.
Manoel Manghi from Toulouse University in France and his colleagues have adopted a seemingly playful approach to examining what happens to a double stranded molecule of DNA when it is stretched to the breaking point, in a study about to be published in EPJ E.
Instead of using optical tweezers to stretch DNA as
previously done in experimental settings, the authors
focused on using a theoretical model to account for the
structural deformations of DNA and determine how
its mechanical characteristics could explain
certain biological processes.
Over fifteen years ago, scientists discovered that DNA
undergoes two structural transitions when pulled from
both ends. The problem is that in experimental
conditions these two transitions can overlap and
become more difficult to observe.
Instead, Manghi and colleagues relied on a standard
mathematical tool referred to as a ‘coupled discrete
wormlike chain-Ising model’ to simulate DNA
stretching and match experimental observations.
Thanks to their theoretical approach, the authors confirmed that after overcoming initial resistance to stretching, at a force of around 65 piconewtons (pN) in strength, the DNA stretches to almost twice its original length while also becoming less rigid.
They also confirmed the other known structural transition occurring at around 135 pN. Although the critical forces of both transitions depend on the DNA sequence, they found it is the second one that most depends on it.
Beyond 135pN, DNA strands start peeling apart into single stranded DNAs that are similar to those obtained when DNA is heated up and undergoes thermal denaturation.
Therefore, this mathematical model bridges the gap between force-induced mechanical stretching and thermal denaturation and could potentially help us to understand how DNA performs its biological functions as in its' interaction in the production of proteins, and how it is packaged into viruses.
M. Manghi, N. Destainville, J.Palmeri (2012) Mesoscopic models for DNA stretching under force: new results and comparison to experiments, European Physical Journal E 35: 110, DOI 10.1140/epje/i2012-12110-2
The full-text article is available for journalists on request.
Original article: http://www.springer.com/about+springer/media/springer+select?SGWID=0-11001-6-1393672-0