Breaks in DNA happen all the time, whether due to radiation or the error-prone process of duplicating DNA for cell division. If those breaks are repaired incorrectly, a cell can become cancerous. Now, using a plate of glass and a tiny magnetic bead, scientists in Holland have watched a repair process called homologous recombination. Cees Dekker of the Delft University of Technology and his colleagues suspended individual strands of DNA between the glass and the bead. Also present was an enzyme that broke the DNA, along with another enzyme, RecA (shown here as transparent blobs). The researcher...
Credit: TU Delft/Thijn van der Heijden and Frank van Heesch

CELL CYCLE. Eddy De Robertis, a developmental biologist at the University of California, Los Angeles, and his colleagues have discovered that when cells divide, the mother cell holds on to garbage -- proteins slated for destruction (shown in green), leaving the daughter cell unencumbered as it starts life. De Robertis thinks the build-up of cellular garbage may presage cell suicide.
Credit: De Robertis

A dividing human embryonic stem cell at metaphase separates cellular garbage (shown in green), storing it around the centosome -- the cellular hub from which emenates molecular rails (red) that chromosomes (blue) will ride as the cell divides.
Credit: De Robertis

A) A human embryonic stem cell at telophase, the final stage of the cell cycle. At this stage chromosomes (blue) are separated and encased in nuclear membranes in both the mother cell and daughter cell. Although proteins slated for destruction (green) are congregate in the mother cell, the garbage proteins are not associated with the mitotic apparatus (red) -- a molecular railroad that ships chromosomes to their final cellular destination. B) Both cells that result from a division of embryonic stem cells are stem cells, even though one cell gets stuck with all the undegraded proteins (green)....
Credit: De Robertis

Tasmanian tigers were hunted to extinction in the wild in the early 1900s, and the last tiger, or thylacine, died in captivity in 1936. But now scientists have resurrected a bit of the thylacine's DNA in a mouse.
Credit: Tasmanian Museum and Art Gallery