restriction enzyme A bacterial enzyme that cuts DNA molecules at discrete base-pair locations.

retentate The part of a mixture that is held back by a filter because of its size, shape, and/or charge.

retention time The period of time between initial application of an elution buffer and the exit from the column of a particular sample component.

RIA Radioimmunoassay; a bioanalytical method that uses specific antibodies and radiolabeled detector molecules to quantitate a defined analyte in mixtures. For safety considerations, many immunoassays are now performed using dyes or other markers in lieu of the radioactive label.

RNA Ribonudeic acid; the nucleic acid based on ribose (a sugar) and the nucleotides G, A, U, and C. It translates the information encoded by DNA into amino acid sequences the cell uses to make proteins. Similar to DNA but based on ribose, and with the base uracil (U) in place of thymine (T). Various forms of RNA are found: mRNA (messenger RNA); tRNA (transfer RNA); and rRNA (ribosomal RNA). Most RNA molecules are single-stranded, although they can form double-stranded units.

RNAi RNA interference; a system that regulates what genes are active and how active they are. Two types of RNA molecules, microRNA (miRNA) and small interfering RNA (siRNA), are central to RNA interference.

risk The combination of the probability of occurrence of harm and the severity of that harm. [From ICH Q9; see also ISO/IEC Guide 51]

risk acceptance The decision to accept risk. [From ICH Q9; see also ISO Guide 73]

risk analysis The estimation of the risk associated with the identified hazards. [From ICH Q9]

risk assessment A systematic process of organizing information to support a risk decision to be made within a risk management process. It consists of the identification of hazards and the analysis and evaluation of risks associated with exposure to those hazards. [From ICH Q9]

risk communication The sharing of information about risk and risk management between the decision maker and other stakeholders. [From ICH Q9].

risk control Actions implementing risk management decisions. [From ICH Q9; see also ISO Guide 73]

risk evaluation The comparison of the estimated risk to given risk criteria using a quantitative or qualitative scale to determine the significance of the risk. [From ICH Q9]

risk identification The systematic use of information to identify potential sources of harm (hazards) referring to the risk question or problem description. [From ICH Q9]

risk management The systematic application of quality management policies, procedures, and practices to the tasks of assessing, controlling, communicating, and reviewing risk. [From ICH Q9]

risk reduction Actions taken to lessen the probability of occurrence of harm and the severity of that harm. [From ICH Q9]

risk review Review or monitoring of output/results of the risk management process considering (if appropriate) new knowledge and experience about the risk. [From ICH Q9]

robust Strongly formed or constructed, sturdy; a product or process that doesn't break easily or remains stable and (for a process) reproducible despite physical and chemical stress or varying conditions.

roller bottle A container with large growth surfaces in which cells can be grown in a confluent monolayer. The bottles are rotated or agitated to keep cells in contact with growth media, but they require extensive handling, labor, and media. In large-scale vaccine production, roller bottles have been replaced by microcarrier culture systems that offer the advantage of scale-up, minimizing contamination.

R subgroup (or side chain) The group of atoms that differs among different amino acid molecules and thus determines their diverse chemical properties; for example, the R subgroup on a Gly molecule is simply a hydrogen atom, on an Ala it is a methyl complex (a carbon atom and three hydrogens), and on Glu it is a combination of carbon, oxygen, nitrogen, and hydrogen atoms.