If a cell is actively synthesizing and secreting proteins, it requires specific morphology. The nucleus of such a cell contains active chromatin or euchromatin permissive for transcription predominantly. Since any transcription means unwrapping of chromosomes, euchromatin is a fine granular, moderately electron-dense material. Being more closely packaged, transcriptionally inactive heterochromatin is usually found in the nuclear periphery as islands of varying size. In the cell nucleus, the nucleoli #1, #2 are well distinguished. An increase of nucleoli number is taken for activation of supplementary nucleolar organizing regions. The nucleoli represent a site for further production and accumulation of ribosomal components, namely rRNA and pre-ribosomal protein particles. A nucleolus contains: 1) amorphous part, 2) nucleolus-associated chromatin or nucleolar chromatin (in humans, it comprises some parts of chromosome 13, 14, 15, 21, and 22), 3) fibrous region with a fibrillar center and 4) granular component. All nucleolar components contain growing pre-ribosomal particles.

In the karyoplasm (nucleoplasm), there is a group of structural protein components and factors that control transcription; sometimes it is defined as a special structure called nuclear matrix.

The nucleus is surrounded by the nuclear envelope consisting of two lipid membranes (an inner one and an outer one). A narrow perinuclear space between the nuclear membranes communicates with cisterns of the endoplasmic reticulum.

In the perinuclear space, one may distinguish some large tiered granules that are β-granules of glycogen #1, #2, #3, comprising smaller α-granules; mitochondria #1, #2; single cisterns of endoplasmic reticulum.