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Prostate cancer cells, confocal light micrograph. The cells' nuclei are yellow. Stress granules (orange) have accumulated in the cells' cytoplasm due to oxidative stress (an increase of oxidants, such as free radicals, that are produced when cells metabolise oxygen). Free radicals are highly reactive. They damage molecules in the cell and can cause cancer. Messenger ribonucleic acid (mRNA) that is not coding for stress-induced proteins accumulates in the stress granules. This stops the production of non-vital proteins while the cell is adjusting to the stress. If the stress is severe the cell will undergo apoptosis, a programmed cell death. (KEYSTONE/SCIENCE PHOTO LIBRARY/Nancy Kedersha)