Anticodon • The three nucleotides in transfer RNA that pair with a complementary triplet (a codon) in messenger RNA.

Central dogma • The statement that information flows from DNA to RNA to polypeptide (in retroviruses, there is also information flow from RNA to cDNA).

Chromosomal mutation • Loss of or changes in position/direction of a DNA segment on a chromosome.

Codon • Three nucleotides in messenger RNA that direct the placement of a particular amino acid into a polypeptide chain. (Contrast with anticodon.)

Conditional mutations • Mutations that show characteristic phenotype only under certain environmental conditions such as temperature.

Deletion • A mutation resulting from the loss of a continuous segment of a gene or chromosome. Such mutations never revert to wild type. (Contrast with duplication, point mutation.)

Duplication (genetic) • A mutation resulting from the introduction into the genome of an extra copy of a segment of a gene or chromosome.

Elongation • Growth of a plant axis or cell primarily in the longitudinal direction.

Frame-shift mutation • A mutation resulting from the addition or deletion of one or two consecutive base pairs in the DNA sequence of a gene, resulting in misreading mRNA during translation and production of a nonfunctional protein. (Contrast with missense mutation, nonsense mutation, synonymous mutation.)

Induced mutation • A mutation resulting from treatment with a chemical or other agent.

Initiation complex • Combination of a ribosomal light subunit, an mRNA molecule, and the tRNA charged with the first amino acid coded for by the mRNA; formed at the onset of translation.

Inversion • A rare 180° reversal of the order of genes within a segment of a chromosome.

Messenger RNA (mRNA) • A transcript of one of the strands of DNA; carries information (as a sequence of codons) for the synthesis of one or more proteins.

Missense mutation • A nonsynonymous mutation, or one that changes a codon for one amino acid to a codon for a different amino acid. (Contrast with frame-shift mutation, nonsense mutation, synonymous mutation.)

Mutation • A detectable, heritable change in the genetic material not caused by recombination.

Nonsense mutation • Mutations that prematurely terminate a polypeptide by changing a codon for an amino acid to one of the codons (UAG, UAA, or UGA) that signal termination of translation. (Contrast with frame-shift mutation, missense mutation, synonymous mutation.)

Phosphorylation • The addition of a phosphate group.

Point mutation • A mutation that results from a small, localized alteration in the chemical structure of a gene; can revert to wild type. (Contrast with deletion.)

Polysome (polyribosome) • A complex consisting of a threadlike molecule of messenger RNA and several (or many) ribosomes. The ribosomes move along the mRNA, synthesizing polypeptide chains as they proceed.

Promoter • The region of an operon that acts as the initial binding site for RNA polymerase.

Proteolysis [protein + Gk. lysis: break apart] • An enzymatic digestion of a protein or polypeptide.

Retrovirus • An RNA virus that contains reverse transcriptase. Its RNA serves as a template for cDNA production, and the cDNA is integrated into a chromosome of the mammalian host cell.

RNA (ribonucleic acid) • An often single stranded nucleic acid whose nucleotides use ribose rather than deoxyribose and in which the base uracil replaces thymine found in DNA. Serves as genome from some viruses. (See rRNA, tRNA, mRNA, and ribozyme.)

RNA polymerase • An enzyme that catalyzes the formation of RNA from a DNA template.

Signal recognition particle (SRP) • A complex of RNA and protein that recognizes both the signal sequence on a growing polypeptide and receptor protein on the surface of the ER.

Signal sequence • The sequence of a protein that directs the protein through a particular cellular membrane.

Silent mutation • A change in gene sequence that, due to the redundancy of the genetic code, has no effect on the amino acid produced, and thus no effect on the protein phenotype. See synonymous mutation.

Start codon • The mRNA triplet (AUG) that acts as a signal for the beginning of translation at the ribosome. (Compare with stop codons.)

Stop codons • The mRNA codons that signal the end of protein translation at the ribosome: UAG, UGA, UAA.

Termination • The end of protein synthesis triggered by a stop codon which binds release factor that causes the polypeptide to release from the ribosome.

Transcription • The synthesis of RNA, using one strand of DNA as the template.

Transfer RNA (tRNA) • A family of double stranded RNA molecules. Each kind of tRNA carries a specific amino acid and anticodon that will pair with the complementary codon in mRNA during translation.

Translation • The synthesis of a protein (polypeptide). This occurs on ribosomes, using the information encoded in messenger RNA.

Translocation • (1) In genetics, a rare mutational event that moves a portion of a chromosome to a new location, generally on a nonhomologous chromosome. (2) In vascular plants, movement of solutes in the phloem.

Uracil (U) • A pyrimidine base found in nucleotides of RNA.