Cell and Tissue Characteristics

I

n most organisms, the cell is the smallest functional unit that can retain the characteristics necessary for life. Cells are organized into larger functional units called tis­sues based on their embryonic origin. These tissues com­bine to form the various body structures and organs. Although the cells of different tissues and organs vary in structure and function, certain characteristics are common to all cells. Cells are remarkably similar in their ability to exchange materials with their immediate environment, obtaining energy from organic nutrients, synthesizing com­plex molecules, and replicating themselves. Because most disease processes are initiated at the cellular level, an under­standing of cell function is crucial to understanding the disease process. Some diseases affect the cells of a single organ, others affect the cells of a particular tissue type, and still others affect the cells of the entire organism. This chap­ter discusses the structural and functional components of the cell, integration of cell function and growth, move­ment of molecules such as ions across the cell membrane and membrane potentials, and tissue types.

Functional Components of the Cell

After you have completed this section of the chapter, you should be able to meet the following objectives:

♦ List the major components of the cell protoplasm

♦ State why the nucleus is called the "control center” of
the cell

Explain the relationships among DNA, genes, and

chromosomes

Name the three types of RNA and describe their role in

protein synthesis

List the cellular organelles and state their functions

State four functions of the cell membrane

Although diverse in their organization, all eukaryotic cells have in common structures that perform unique func­tions. When seen under a light microscope, three major components of the cell become evident: the nucleus, the cytoplasm, and the cell membrane (Fig. 4-1).