APPENDIX C: BIOINFORMATICS GLOSSARY 271
Adenine: one of the nitrogenous bases that has a double - ring structure, clas-
sifi ed as a purine, found in DNA and RNA.
A DNA: a more dehydrated form of DNA than the typical, B form. It is more
compact, with 11 nitrogen bases per turn of the helix. RNA – DNA and
RNA – RNA helices typically exist in this form.
Agents: software modules that can search the Internet for data. These modules
are independent and autonomous.
Algorithm
1,2
: a series of steps defi ning a procedure or formula for solving a
problem that can be coded into a programming language and executed.
Bioinformatics algorithms typically are used to process, store, analyze, visu-
alize, and make predictions from biological data.
Alignment: the result of a comparison of two or more gene or protein
sequences in order to determine their degree of nitrogen base or amino
acid similarity or dissimilarity. Sequence alignments are used to determine
the similarity, homology, function, or other degree of relatedness between
two or more genes or gene products.
Allele: a given form of a gene that occupies a specifi c position or locus on a
chromosome.
Alpha carbon: the central carbon atom in an amino acid to which side chains
(R groups) are bound.
Alpha helix
1,2
: one of two types of protein secondary structure. An α - helix is
a tight helix that results from the hydrogen bonding of the carboxyl (CO)
group of one amino acid to the amino (NH) group of another amino acid,
four residues away (toward the carboxyl terminus).
Alternative splicing: the production of two or more mRNA molecules from
a single hnRNA by using different splice junctions.
Amino acid: one of the 20 chemical building blocks that are joined by amide
(peptide) linkages to form a polypeptide chain of a protein.
Amphipathic: a molecule that has hydrophilic and hydrophobic characteris-
tics simultaneously. This term is often used to describe large proteins with
several domains of composed of different types of amino acid residues.
Annotation: a collection of comments, notations, references, and citations,
either in free format or utilizing a controlled vocabulary, that together
describe all the experimental and inferred information about a gene or
protein. Annotations can also be applied to the description of other biologi-
cal systems. Batch, automated annotation of bulk biological sequence is one
of the key uses of bioinformatics tools.
Anticodon: the triplet of contiguous bases on tRNA that binds to the codon
sequence of nucleotides on mRNA (e.g., the codon for glycine is GGG, on
mRNA; the anticodon for glycine is CCC, on tRNA).
Antigen: any foreign molecule that stimulates an immune response in a ver-
tebrate organism. Many antigens are proteins, such as the surface proteins
of foreign organisms. Antigens bind to antibodies.