DNA Structure and
DNA provides the set of coded instructions required by every
organism for specifying its traits. The DNA molecule
also provides for a reliable way for parents to pass their
genetic code from one generation to the next.
Heredity refers to this passage
of these instructions from one generation to another.
DNA is a double stranded molecule which has the shape of a
twisted ladder. This shape is called an alpha
helix. The sides of this twisted ladder are
composed of alternating phosphate and deoxyribose sugar units,
while the rungs of the ladder are composed of pairs of
nitrogenous bases. These bases are called adenine
(A), thymine (T), guanine (G), and cytosine (C).
These bases exist in pairs on the rungs of the ladder with A
always pairing with T and G pairing with C. This
principle is sometimes called complementary base pairing.
(The saying G CAT provides a means of remembering this idea.)
Structure of the DNA molecule
Location of DNA
Hereditary information is contained
in genes, which are composed of DNA, located in
the chromosomes of each cell. Chromosomes
are found in the nucleus of each cell.
The Gene Chromosome Model
Each gene carries a separate
piece of information. An inherited trait of an individual can
be determined by one genes, but is usually determined by the
interaction of many different genes.
A single gene can influence more than one trait. A human
cell contains many thousands of different genes coding for
many different traits. Changes in the sequence of the
DNA molecule and therefore the gene are called mutations.
A mutation may change the manner in which a trait is expressed
by an organism.