Key Terms in Molecular Biology and Genetics

Proteins and Gene Expression

• Activator: A DNA-binding protein that positively regulates the expression of one or more genes, i.e., the rate of transcription increases when an activator is bound to DNA. It is a positive modulator.
• Aminoacyl-tRNA Synthetase: Allosteric enzymes that catalyze the synthesis of aminoacyl-tRNA at the expense of ATP energy.
• Attenuation/Attenuator: An RNA sequence involved in the regulation of the expression of certain genes. The terminator functions in transcription.
• Inductor: A signal molecule that, when coupled with a regulatory protein, produces an increase in the expression of a particular gene.
• Leucine Zipper: A structural protein motif involved in protein-protein interactions in many eukaryotic regulatory proteins. It consists of two alpha helices interacting; the presence of leucine residues every seven residues is a prominent feature of interacting surfaces.
• Zinc Finger: A protein motif involved in specialized DNA recognition by some DNA-binding proteins. It is characterized by a single zinc atom coordinated with four cysteine residues, two histidine residues, or two cysteine and two histidine residues.

DNA, RNA, and Genetic Material

• Antibiotic: An organic product formed and secreted by different species of microorganisms and plants. Antibiotics are toxic to other species and probably have some defensive function.
• cDNA Cloning: DNA used in DNA cloning, normally obtained using reverse transcriptase. It is complementary to a specific mRNA.
• Cloning: The production of large amounts of identical DNA molecules from a single DNA molecule or progenitor cell in cells or organisms.
• Codon: A sequence of three adjacent nucleotides in a nucleic acid that codes for a specific amino acid.
• Genetic Code: All the triplet codewords in DNA that encode amino acids in proteins.
• Genomic Library: A DNA library containing DNA segments that represent all or most of an organism's genome sequence.
• Chromosome: A large, single molecule of DNA and associated proteins containing many genes; it stores and transmits genetic information.
• Filamentous Chromatin: A complex of DNA, histones, and other proteins that constitute a eukaryotic chromosome.
• Denaturing: The partial or complete unfolding of the specific native conformation of a polypeptide chain, protein, or nucleic acid.
• DNA (Deoxyribonucleic Acid): A polynucleotide with a specific sequence of deoxyribonucleic units covalently linked by 3',5'-phosphodiester bonds; it acts as a carrier of genetic information.
• DNA Ligase: An enzyme that creates a phosphodiester bond between the 3' end of one segment of DNA and the 5' end of another.
• Exon: A segment of a eukaryotic gene encoding a portion of the final product of a gene. It is a portion that remains after post-transcriptional processing and is translated into protein or incorporated into the structure of an RNA.
• Gene: A segment of a chromosome that encodes a single polypeptide chain or functional RNA molecule.
• Intron: A sequence of nucleotides in a gene that is transcribed but eliminated by splicing before translation.
• Mutation: A heritable change in the nucleotide sequence of a chromosome.
• Restriction Endonucleases: Endonucleases that produce site-specific cuts in both strands of DNA at points within or near the specific site recognized by the enzyme. They are important tools in genetic engineering.