The many and complex chemical reactions that are
necessary to maintain life can take place only in a delicately balanced
Living cells, such as the
cheek cells shown on the borders of this
page, are the life support chambers that maintain this special
environment. Cheek cells are the cells that are collected for use in DNA
testing for genealogy. (Click the thumbnail to
see Mr. James Dorsey collecting cheek cells for the Dorsey/Kelley
All living organisms are made
up of cells.
Just as a brick is the basic
unit of structure of a house, a cell is the basic unit of structure of all
living things. All organisms consist of one or more cells.
New cells can be formed only by the division of existing cells. A
plant or animal starts as a single cell and grows by increasing the number
of cells. The human body contains approximately 100 trillion cells,
most of which are less than a tenth of a millimeter across.
An organism acquires energy by breaking
down food within its cells. It then uses this energy to maintain each
internal chemical environment, to build organic molecules, to grow, and to
reproduce by cell division.
Most cells (excluding bacteria)
have three main parts:
1. The cell membrane is a thin but tough covering made of lipids and proteins that forms the
outside of the bag. The cell membrane protects the inner contents of the
cell, gives the cell shape and supports and controls what goes in and out
of the cell.
2. The cytoplasm (means cell substance) contains water, various salts, and many large
macromolecules. The cytoplasm also contains a variety of smaller subunits
or compartments of the cell called organelles
which perform various tasks.
nucleus houses the cell’s genetic material (DNA and RNA) and proteins.
The genetic material
contains directions for making the cell’s proteins.
Of particular interest
to the molecular genealogist, are the
and one of the smaller
organelles found in the cytoplasm, the
Fig. 1 adapated from the National Human Genome Glossary:
For a simulated, interactive look at cheek cells
through a microscope try: