Electron micrograph of a nucleus, showing the heterochromatin (HC) and euchromatin (EC). Unlabeled arrows indicate the nucleolus-associated chromatin around the nucleolus (NU). Arrowheads indicate the perinuclear cisterna. Underneath the cisterna is a layer of heterochromatin, the main component of the so-called nuclear membrane seen under the light microscope. x26,000.
Illustration showing the structure, the localization, and the relationship of the nuclear lamina with chromosomes. The drawing also shows that the nuclear pore complex is composed of two protein rings in an octagonal organization. From the cytoplasmic ring, long filaments penetrate the cytosol, and from the intranuclear ring arise filaments that constitute a basketlike structure. The presence of the central cylindrical granule in the nuclear pore is not universally accepted.
Electron micrographs of nuclei showing their envelopes composed of two membranes and the nuclear pores (arrows). A, B: Transverse sections; C: A tangential section. Chromatin, frequently condensed below the nuclear envelope, is not usually seen in the pore regions. x80,000.
Electron micrograph obtained by cryofracture of a rat intestine cell, showing the two components of the nuclear envelope and the nuclear pores. (Courtesy of P Pinto da Silva.)
Simplified representation of two nuclear pore complexes. In this model, the final nuclear portion is seen to be a more continuous structure, in the shape of a ring.