The Structure of the DNA Molecule
Glossary

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Adenine: A nitrogenous base. Pairs with thymine in DNA
molecules.

Bacteriophage: A virus whose host is a bacterium. Also called
phage.

Base: See nitrogenous
base.

Base Pair: Two nitrogenous bases held together by weak bonds. In
a DNA molecule adenine always pairs with thymine while cytosine always
pairs with guanine. Thus, one DNA strand directs the synthesis of the
other strand. This specificity of DNA base pairing is what enables
accurate replication of a DNA molecule.

Chromosome: a self-replicating genetic structure, composed
primarily of proteins and DNA, which carry nucleotide sequences known as
genes.

Complementary base pair: a pair of bases in which the identity
of one base defines the identity of its partner base. E.g.: In a DNA
molecule there are two complementary base pairs--Adenine and thymine, and
guanine and cytosine.

Cytosine: A nitrogenous base. Pairs with guanine in DNA
molecules.

DNA (deoxyribonucleic acid): the molecule that encodes genetic
information. DNA is composed of two anti-parallel strands which wind about
a common axis to form a double helix. Each strand of DNA is composed of a
linear array of nucleotides bonded in such a way that the bases extend
toward the central axis of the molecule while the two backbones are
composed of alternating sugar and phosphate subunits. The bases of the two
strands are weakly bonded to each other in a complementary fashion. In
other words, an adenine is always bound to a thymine while a cytosine is
always bound to a guanine.

Gene: An ordered sequence of nucleotides which act as the
functional subunit of hereditary information. The collection of genes in
an organism determine the characteristics of that organism.

Guanine: A nitrogenous base. Pairs with cytosine in DNA
molecules.

Meiosis: the process of cell division in which a single cell
produces four daughter cells each of which contains half of the number of
chromosomes of the parent cell. For example, a single diploid
spermatogonium (primordial germ cell) will divide meiotically to produce 4
haploid sperm cells.

Mitosis: the process of cell division in which a single cell
produces two daughter cells which are identical to on another, and to the
original parent cell.

Nitrogenous base: a molecule with the
properties of a base, which also contains the element nitrogen.

Nucleic acid: a large molecule composed of repeating nucleotides

Nucleotide: A subunit of DNA or RNA composed of a nitrogenous
base, a phosphate molecule, and a pentose sugar molecule.

Pentose sugar: A sugar molecule containing five carbon atoms.
E.g.: deoxyribose.

Phage: A virus which infects a bacterial cell. Also called a
Bacteriophage.

Purine: A nitrogen- containing, single ring compound that occurs
in nucleic acids. In DNA molecules, the purines are adenine and guanine.

Pyrimidine: A nitrogen containing, double ring compound that
occurs in nucleic acids. In DNA molecules, the pyrimidines are cytosine
and thymine.

Radioactive phosphorus (32P): radioactive isotope of 31P, an
element found in DNA molecules.

Radioactive sulfur (35S): radioactive isotope of 32S, an element
found in proteins

T Phages: A phage which infects Escherichia coli. Viral
parasites of this type are labeled T1 through T7. T2 was the first phage
observed under the electron microscope.

Thymine: A nitrogenous base. Pairs with adenine in DNA
molecules.

Virus: A particle consisting of a nucleic acid core surrounded
by a protein coat. New virus particles can only be produced by a cell
which is infected by the virus.

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