Basic Parts Of A Cell

figure 4-6

Most animal cells have a cell membrane, a nucleus, and a variety of other organelles embedded in a watery substance. The surface of the cell membrane can be seen in (a). The organelles inside the cell are labeled in the diagram (b).

Despite the diversity among cells, three basic features are common to all cell types. All cells have an outer boundary, an interior substance, and a control region.

Plasma Membrane

The cell's outer boundary, called the plasma membrane (or the cell membrane), covers a cell's surface and acts as a barrier between the inside and the outside of a cell. All materials enter or exit through the plasma membrane. The surface of a plasma membrane is shown in Figure 4-6a.

Cytoplasm

The region of the cell that is within the plasma membrane and that includes the fluid, the cytoskeleton, and all of the organelles except the nucleus is called the cytoplasm. The part of the cytoplasm that includes molecules and small particles, such as ribosomes, but not membrane-bound organelles is the cytosol. About 20 percent of the cytosol is made up of protein.

Control Center

Cells carry coded information in the form of DNA for regulating their functions and reproducing themselves. The DNA in some types of cells floats freely inside the cell. Other cells have a membrane-bound organelle that contains a cell's DNA. This membrane-bound structure is called the nucleus. Most of the functions of a eukaryotic cell are controlled by the cell's nucleus. The nucleus is often the most prominent structure within a eukaryotic cell. It maintains its shape with the help of a protein skeleton called the nuclear matrix. The nucleus of a typical animal cell is shown in Figure 4-6b.

Nuclear pore Nuclear envelope Nucleolus

Mitochondrion

Microfilaments

Lysosome

Golgi apparatus

Nuclear pore Nuclear envelope Nucleolus

Mitochondrion

Microfilaments

Lysosome

Golgi apparatus

Ribosomes

Cell membrane

Microtubules

Rough ER

Smooth ER

-Nucleus

Ribosomes

Cell membrane

Microtubules

Rough ER

Smooth ER

figure 4-7

A prokaryotic cell lacks a membrane-bound nucleus and membrane-bound organelles. Most prokaryotic cells are much smaller than eukaryotic cells are.

figure 4-7

A prokaryotic cell lacks a membrane-bound nucleus and membrane-bound organelles. Most prokaryotic cells are much smaller than eukaryotic cells are.

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