Looking for the heartbeat of cellular networks

Dec 16, 2009

Our cells' molecules form an intricate network of interactions. Today's techniques, however, can only be used to measure individual molecular reactions outside the cells. Since molecular concentrations are much higher in cells than in the laboratory, scientists suspect that the kinetics of molecular reactions in living cells differ substantially from external probes.

"We expected the cellular reaction speed to be higher," confirms LMU biophysicist Professor Dieter Braun. "However, our novel optical approach showed that - depending on the length of the strands - the coupling of DNA-strands inside living cells can be both faster and slower than outside." Data yielded from living cells are highly valuable for the development of models to understand the complex interactions as well as pathological processes in biological cells. Braun and his team now plan to probe a variety of molecular reactions in living cells, visualizing the heartbeat of . (PNAS online, 14 November 2009)

In their work, the scientists investigated the hybridization - the coupling and de-coupling - of two DNA-strands, which they introduced into living cells. To determine the reaction time constant they used an to induce temperature oscillations of different frequencies in the cell and measured the concentration of the reaction partners, namely of coupled and de-coupled DNA. At low frequencies, these concentrations followed the temperature oscillations, whereas at higher frequencies they experienced a phase delay and oscillated with diminished amplitude. Both delay time and amplitude decrease, were evaluated to obtain the reaction time constant.

The team determined the concentrations using the so-called fluorescent energy transfer (FRET), which takes place between two chromophores at a certain spatial distance. They applied a FRET pair to the DNA-strands such that occurred only if the strands were coupled. The chromophores were excited with a stroboscopic lamp and a CCD camera registered time and amplitude of the fluorescence, thus visualizing the concentration alterations with a spatial resolution of about 500 nanometres. The experiments revealed that DNA-strands comprising 16 units, the so-called bases, showed a sevenfold higher reaction speed compared to values determined outside living cells.

12-base DNA-strands, on the other hand, reacted times five times slower than outside cells. This is a surprising result, since kinetics of molecular reactions has been assumed to be always faster inside cells, where much higher molecular concentrations prevail. "Apparently cells modulate the reaction speed in a highly selective way," says Braun. "The measurements provide valuable insight into in vivo kinetic data for the systematic analysis of the complexity of biological cells," adds Ingmar Schön, who conducted the demanding experiments. The scientists are now planning to probe a wide variety of molecular reactions in , visualizing the heartbeat of cellular networks.

Explore further: Toxin targets discovered

More information: "Hybridization Kinetics is Different Inside Cells," Ingmar Schoen, Hubert Krammer, Dieter Braun, PNAS online, 14 November 2009

Provided by Ludwig-Maximilians-Universität München

not rated yet
add to favorites email to friend print save as pdf

Related Stories

Models begin to unravel how single DNA strands combine

Oct 05, 2009

(PhysOrg.com) -- Using computer simulations, a team of University of Wisconsin-Madison researchers has identified some of the pathways through which single complementary strands of DNA interact and combine to form the double ...

Scientists see DNA get 'sunburned' for the first time

Feb 01, 2007

For the first time, scientists have observed DNA being damaged by ultraviolet (UV) light. Ohio State University chemists and their colleagues in Germany used a special technique to watch strands of DNA in the laboratory sustain ...

Study: Cells prevent DNA repair

Nov 23, 2005

Scientists say they've discovered cells co-opt the machinery that usually repairs broken strands of DNA to protect the integrity of chromosomes.

Structure relevant to cell growth

Oct 22, 2005

Utah researchers found a special type of molecular structure that helps keep genes properly turned off until the structure is ejected.

Recommended for you

Toxin targets discovered

4 hours ago

Research that provides a new understanding of how bacterial toxins target human cells is set to have major implications for the development of novel drugs and treatment strategies.

New method for quickly determining antibiotic resistance

11 hours ago

Scientists from Uppsala University, the Science for Life Laboratory (SciLifeLab) in Stockholm and Uppsala University Hospital have developed a new method of rapidly identifying which bacteria are causing an infection and ...

Cohesin molecule safeguards cell division

Nov 21, 2014

The cohesin molecule ensures the proper distribution of DNA during cell division. Scientists at the Research Institute of Molecular Pathology (IMP) in Vienna can now prove the concept of its carabiner-like ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.