Figure 13. Schematic drawing of an animal cell.
STRUCTURAL COMPONENTS OF A CELL
a. Nucleus. The nucleus plays a central role because it is from this structure
that information is distributed which guides the life processes of the cell. In particular,
the nucleus plays a central role in cellular reproduction. Two types of structures found
in the nucleus are chromosomes and nucleoli. Chromosomes are distinct only during
cell division. They are composed of both nucleic acid and protein, and contain genes
(basic hereditary units). Nucleoli are darkly staining ovoid bodies whose chief chemical
constituent is ribonucleic acid (RNA). When protein systhesis is occurring in the cell,
nucleoli are involved in interactions between the nucleus and cytoplasm.
b. Centrioles. Centrioles are found in pairs in the cytoplasm. They are
cylindrical bodies oriented at right angles to one another. Their primary function is to
assist in the division of the cell.
c. Endoplasmic Reticulum. The endoplasmic reticulum was so named
because it was once thought to be confined entirely to the endoplasm (that part of the
cytoplasm close to and surrounding the nucleus). It is now known to extend to the
peripheral regions of the cell and is sometimes attached to the cell membrane. It is a
complex network of thin membranebound cavities that vary considerably in shape.