Programming with the Light Switch (IMAGE) University of Freiburg Caption Exposure to light releases the molecule ATP. It provides the energy for an enzyme (blue) that joins DNA building blocks into a strand. Another enzyme (green) separates the strand at these binding sites so that the strand is dynamically lengthened and shortened. Credit Illustration: Michal Rössler Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.