Electron Microscopy: Active Genes

A. Electron micrograph of active genes. During transcription the compact chromatin (the dark areas on the lower left side) opens up and long loops of DNA being transcribed is visable (two loops are indicated with arrows). On the loop of DNA the growing RNP (pre-mRNA+protein) being synthesized can be seen.

B. Schematic presentation of a transcription loop. The base line inside the loop represents the DNA. Along the DNA axis many RNA polymerases (too small to be visible at this resolution) synthesize the RNA that grow longer and longer from the beginning (left) to the end (right) of the gene. The RNA is packed with proteins into RNP and forms a globular structure growing in size and released at the end of the gene.

C. Magnification of one of the loops from figure A. At this maginification it is easier to compare the micrograph with the schematic representation in figure B.

Images kindly provided by Bertil Daneholt, Department of Cell and Molecular Biology, Karolinska Institutet. Reference: Insect Ultrastructure, Vol 1, Plenum Publishing Corporation 1982

next picture »