Bacteria: Bacteria (singular: bacterium) are a major group of living organisms. The term "bacteria" has variously applied to all prokaryotes or to a major group of them, otherwise called the eubacteria. Here, bacteria is used specifically to refer to the eubacteria. Bacteria are the most abundant of all organisms. They are ubiquitous in soil, water, and as symbionts of other organisms. Many pathogens are bacteria.

Bacteriophage: A virus that infects bacteria. The bacteriophage DNA has served as a basis for cloning vectors, and is also utilized to create phage libraries containing human or other genes.

Beta sheet: A three dimensional arrangement taken up by polypeptide chains that consists of alternating strands linked by hydrogen bonds. The alternating strands together form a sheet that is frequently twisted. One of the secondary structural elements characteristic of proteins.

Base pair: A pair of nitrogenous bases (a purine and a pyrimidine), held together by hydrogen bonds, that form the core of DNA and RNA i.e the A:T, G:C and A:U interactions.

Bioinformatics: The field of endeavor that relates to the collection, organization and analysis of large amounts of biological data using networks of computers and databases (usually with reference to the genome project and DNA sequence information).

Base-pairing: The attachment of one polynucleotide to another -- or one part of a polynucleotide to another part of the same polynucleotide -- by base pairs.

Bit score: The value S' is derived from the raw alignment score S, in which the statistical properties of the scoring system used have been taken into account.

BLAST: A set of programs, used to perform fast similarity searches.

Block: Conserved ungapped patterns approximately 3-60 amino acids in lenght in a set of related protein.

Browser: Program used to access sites on the WWW. Hyper Text Markup Language (HTML) enables browsers to represent a web page the same way regardless of computer platform.

Binding site Specific DNA/RNA sequences a protein or protein complex bind. Some examples of protein binding sites are promoters, ribosome entry sites, and replication origins.

Blunt ends Digestions of double-stranded DNA by many restriction enzymes (e.g. EcoR V) generate ends without any single-stranded sequences. Such ends are called blunt ends.