DR ELENA KISELEVA / SCIENCE PHOTO LIBRARY DR ELENA KISELEVA / SCIENCE PHOTO LIBRARY
E. coli DNA. Coloured transmission electron micrograph (TEM) of a relaxed deoxyribonucleic acid (DNA) molecule (yellow) in the bacterium Escherichia coli. Bacteria are prokaryotic organisms. They have a very simple cell structure with no organelles and no nucleus. Their DNA exists as a naked molecule within the cell's cytoplasm. The majority of the DNA forms one molecule known as the nucleoid (yellow). This is usually extensively twisted and folded, or supercoiled, to fit the large molecule into the cell. Here however, the DNA has uncoiled somewhat. Uncoiling occurs to allow replication of the DNA, and therefore replication of the cell.
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