Figure 13.3: Under the electron microscope, DNA molecules undergoing transcription exhibit Christmas-tree-like structures. (a) Electron micrograph of structures similar in appearance to Christmas trees. (b) The trunk of each “Christmas tree” (a transcription unit) represents a DNA molecule; the tree branches are RNA molecules that have been transcribed from the DNA. As the transcription apparatus moves down the DNA, transcribing more of the template, the RNA molecules become longer and longer.
[Part a: Dr. Thomas Broker/Phototake.]