Page 93 - Atlas of Histology with Functional Correlations

membrane (3a) is in contact with the cell cytoplasm (4), whereas the inner

nuclear membrane (3b) is associated with the nuclear chromatin (7). The
nuclear envelope is continuous with the rough endoplasmic reticulum (1), and
the outer nuclear membrane (3a) usually contains ribosomes. At certain intervals
around the nucleus, the two membranes of the nuclear envelope (3) fuse and
form numerous nuclear pores (2, 6).

FIGURE 2.8 ■ Nuclear envelope and nuclear pores. ×110,000.

FUNCTIONAL CORRELATIONS 2.7 ■ Nucleus,

Nucleolus, and Nuclear Pores

The nucleus is the control center of the cell; it stores and processes most of
the cell’s genetic information. The nucleus directs all of the activities of the
cell through the process of protein synthesis and ultimately controls the

structural and functional characteristics of each cell. The cell’s genetic
material, deoxyribonucleic acid (DNA), is visible in the cell in the form of
chromatin. When the cells are not actively producing protein, the DNA is
not condensed and does not stain.

The nucleolus is a dense-staining, nonmembrane-bound structure within
the nucleus. One or more nucleoli may be visible in a given cell. The
nucleolus functions in synthesis, processing, and assembly of ribosomes. In
nucleoli, the ribosomal ribonucleic acid (RNA) is produced and combined
with proteins to form ribosomal subunits. These ribosomal subunits are then

transported to the cell cytoplasm through the nuclear pores to form complete
ribosomes. Consequently, nucleoli are prominent in cells that synthesize
large amounts of proteins.

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