CK12 Life Science

Table 3.1: Comparison of Prokaryotic and Eukaryotic Cells

Feature Prokaryotic cells Eukaryotic cells

DNA Single “naked” circle;

plasmids

In membrane-enclosed

nucleus

Membrane-enclosed

organelles

No Yes

Examples Bacteria Plants, animals, fungi

The main difference between eukaryotic and prokaryotic cells is that eukaryotic cells store
their DNA in a membrane-enclosed nucleus. The presence of a nucleus is the primary
distinguishing feature of a eukaryotic cell. In addition to the nucleus, eukaryotic cells have
othersubcompartments, smallmembrane-enclosedstructurescalledorganelles. Membrane-
enclosed organelles and a nucleus are absent in prokaryotic cells. Eukaryotic cells include
the cells of fungi, animals, protists, and plants.

The Plasma Membrane and Cytosol

Both eukaryotic and prokaryotic cells have a plasma membrane. Theplasma membrane
is a double layer of specialized lipids, known as phospholipids, along with many special
proteins. The function of the plasma membrane, also known as the ”cell membrane,” is to
control what goes in and out of the cell.

Some molecules can go through the cell membrane in and out of the cell and some can’t, so
biologists say the membrane issemipermeable. It is almost as if the membrane chooses
what enters and leaves the cell.

The cell membrane gives the cell an inside that is separate from the outside world. Without
a cell membrane, the parts of a cell would just float away. A cell needs a boundary even more
than we need our skin. Without a cell membrane, a cell would be unable to maintain a stable
internal environment separate from the external environment, what we call homeostasis. You
can learn more about cell membranes in theCell Functionschapter.

Eukaryoticandprokaryoticcellsalsoshareaninternalfluid-likesubstancecalledthecytosol.
The cytosol is composed of water and other molecules, including enzymes that speed up the
cell’s chemical reactions. Everything in the cell - the nucleus and the organelles - sit in
the cytosol. The termcytoplasmrefers to the cytosol and all the organelles, but not the
nucleus.