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Radioimmunoassay (RIA) A test combining
radioisotopes and immunology to detect trace
substances. Such tests are useful for studying antibody
interactions with cell receptors, and can be developed
into clinical diagnostics.
Rational drug design Using the known three-dimensional
structure of a molecule, usually a protein, to design a
drug molecule that will bind to it. Usually viewed as an
alternative to drug discovery through screening many
molecules for biological activity.
Reagent Substance used in a chemical reaction.
Recombinant DNA (rDNA) The DNA formed by
combining segments of DNA from two different
sources.
Regeneration Laboratory technique for forming a new
plant from a clump of plant cells.
Regulatory gene A gene that acts to control the proteinsynthesizing
activity of other genes.
Replication Reproduction or duplication, as of an exact
copy of a strand of DNA.
Replicon A segment of DNA (e.g., chromosome or
plasmid) that can replicate independently.
Repressor A protein that binds to an operator adjacent
to a structural gene, inhibiting transcription of that
gene.
Restriction enzyme An enzyme that breaks DNA in
highly specific locations, creating gaps into which new
genes can be inserted.
Restriction fragment length polymorphism (RFLP) The
variation in the length of DNA fragments produced by
a restriction endonuclease that cuts at a polymorphic
locus. This is a key tool in DNA fingerprinting and
is based on the presence of different alleles in an
individual. RFLP mapping is also used in plant
breeding to see if a key trait such as disease resistance
is inherited.
Reticuloendothelial system The system of macrophages,
which serves as an important defense system against
disease.
Retrovirus A virus that contains the enzyme reverse
transcriptase. This enzyme converts the viral RNA into
DNA, which can combine with the DNA of the host cell
and produce more viral particles.
Rheology Study of the flow of matter such as
fermentation liquids.
Rhizobium A class of microorganisms that converts
atmospheric nitrogen into a form that plants can
utilize for growth. Species of this microorganism grow
symbiotically on the roots of certain legumes, such as
peas, beans and alfalfa.
Ribonucleic acid (RNA) A molecule similar to DNA that
delivers DNA's genetic message to the cytoplasm of a
cell where proteins are made.
Ribosome A cellular component, containing protein and
RNA, that is involved in protein synthesis.
RNA interference A natural process used by organisms to
block protein production.
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