Abstract

Cells, both for eukaryotic and prokaryotic systems, are thermodynamically unstable. This instability is essentially allowed by two elements: on one hand a membrane isolates the cells from the external world, on the other hand many active proteins transform the energy inside the cell. Molecular motors represent a major family of these proteins: the enzymes catalyze ATP hydrolysis, transforming ATP into the more stable ADP . During the hydrolysis reaction the chemical energy stored in ATP is transformed in mechanical power. Hundreds molecular motors are involved in cell motility (migration, muscle contraction, hearing.), intracellular transport, organelle dynamics, mitosis, and DNA replication and transcription. We focus on two “motors”: using a new generation of magnetic tweezers we investigate the dynamics of the Recombinase hRad51. This enzyme promotes the homologous recombination (HR), i.e. the strand exchange between two DNA molecules of identical sequence. HR is the base of two vital mechanisms: the DNA repair, which preserves the genetic integrity, and the DNA shuffle, which introduces genetic diversity and evolution. During this seminar, we also discuss our first attempts to bring the single molecule approach inside the cell.