a. Somatic Cells. Somatic cells are those of a specific individual tissue such as
heart, lung, or liver. Their functions provide life for an individual. Somatic cells give
their daughter cells operating instructions to act like they themselves acted.
b. Gonadal Cells. Gonadal cells ensure a species' continuance. When
creating a new member of the species, the operating or genetic instructions of two cells
interweave, add, subtract, and modify. If either cell has been previously modified, it
cannot pass on the genetic instructions it should.
4-22. DEOXYRIBONUCLEIC ACID AND RIBONUCLEIC ACID
All cells have one common and extremely vital characteristic: they pass on to
their daughter cells operating instructions which are extremely detailed, highly complex,
and an exact duplicate of the instructions they received from their parent cells.
Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are substances found in all
cells and serve as blueprints for cell reproduction.
a. Deoxyribonuclei Acid Molecule. The DNA molecule is a double helix that has
two important functions--replication and control of cellular activities. The fundamental unit
of DNA is the nucleotide, which consists of a phosphate group, a 5-carbon sugar, and a nitrogen
base. There are four nitrogen bases found in DNA--guanine, cytosine, adenine, and
thymine. They are shown in figure 4-11 with different shapes for illustrative purposes.
One end of each nitrogen base is identical to the others. It fits the 5-carbon sugar
perfectly, but it will not fit the phosphate group. The nitrogen bases fit each other only in
specific combinations: guanine with cytosine and adenine with thymine.
Figure 4-11. The 5 nitrogen bases found in DNA.