Molecular Biology Chapter 18 Vocabulary

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Operator

Back 1

In bacterial and phage DNA, a sequence of nucleotides near the start of an operon to which an active repressor can attach. The binding of the repressor prevents RNA polymerase from attaching to the promoter and transcribing the genes of the operon.

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Operon

Back 2

A unit of genetic function found in bacteria and phages, consisting of a promoter, an operator, and a coordinately regulated cluster of genes whose products function in a common pathway.

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Repressor

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A protein that inhibits gene transcription. In prokaryotes, repressors bind to the DNA in or near the promoter. In eukaryotes, repressors may bind to control elements within enhancers, to activators, or to other proteins in a way that blocks activators from binding to DNA.

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Regulatory gene

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A gene that codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes.

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Corepressor

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A small molecule that binds to a bacterial repressor protein and changes the protein’s shape, allowing it to bind to the operator and switch an operon off.

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Inducer

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A specific small molecule that binds to a bacterial repressor protein and changes the repressor’s shape so that it cannot bind to an operator, thus switching an operon on.

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Cyclic AMP (cAMP)

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Cyclic adenosine monophosphate, a ring-shaped molecule made from ATP that is a common intracellular signaling molecule (second messenger) in eukaryotic cells. It is also a regulator of some bacterial operons.

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Activator

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A protein that binds to DNA and stimulates gene transcription. In prokaryotes, activators bind in or near the promoter; in eukaryotes, activators generally bind to control elements in enhancers.

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Differential Gene Expression

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The expression of different sets of genes by cells with the same genome.

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Histone Acetylation

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The attachment of acetyl groups to certain amino acids of histone proteins.

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DNA Methylation

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The presence of methyl groups on the DNA bases (usually cytosine) of plants, animals, and fungi. (The term also refers to the process of adding methyl groups to DNA bases.)

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Epigenetic Inheritance

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Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence of a genome.

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Control Elements

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A segment of noncoding DNA that helps regulate transcription of a gene by serving as a binding site for a transcription factor. Multiple control elements are present in a eukaryotic gene’s enhancer.

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Enhancers

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A segment of eukaryotic DNA containing multiple control elements, usually located far from the gene whose transcription it regulates.

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Alternative RNA splicing

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A type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns.

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Proteasomes

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A giant protein complex that recognizes and destroys proteins tagged for elimination by the small protein ubiquitin.

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microRNAs (miRNAs)

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A small, single-stranded RNA molecule, generated from a hairpin structure on a precursor RNA transcribed from a particular gene. The miRNA associates with one or more proteins in a complex that can degrade or prevent translation of an mRNA with a complementary sequence.

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RNA Interference (RNAi)

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A technique used to silence the expression of selected genes. RNAi uses synthetic double-stranded RNA molecules that match the sequence of a particular gene to trigger the breakdown of the gene’s messenger RNA.

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Small Interfering RNAs (siRNAs)

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One of multiple small, single-stranded RNA molecules generated by cellular machinery from a long, linear, double-stranded RNA molecule. The siRNA associates with one or more proteins in a complex that can degrade or prevent translation of an mRNA with a complementary sequence. In some cases, siRNA can also block transcription by promoting chromatin modification.

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Differentiation

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The process by which a cell or group of cells become specialized in structure and function.

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Morphogenesis

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The cellular and tissue-based processes by which an animal body takes shape.

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Cytoplasmic Determinants

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A maternal substance, such as a protein or RNA, that when placed into an egg influences the course of early development by regulating the expression of genes that affect the developmental fate of cells.

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Induction

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The process in which one group of embryonic cells influences the development of another, usually by causing changes in gene expression.

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Determination

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The progressive restriction of developmental potential in which the possible fate of each cell becomes more limited as an embryo develops. At the end of determination, a cell is committed to its fate.

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Pattern formation

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The development of a multi- cellular organism’s spatial organization, the arrangement of organs and tissues in their characteristic places in three-dimensional space.

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Positional information

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Molecular cues that control pattern formation in an animal or plant embryonic structure by indicating a cell’s location relative to the organism’s body axes. These cues elicit a response by genes that regulate development.

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Homeotic genes

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Any of the master regulatory genes that control placement and spatial organization of body parts in animals, plants, and fungi by controlling the developmental fate of groups of cells.

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Embryonic lethals

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A mutation with a phenotype leading to death of an embryo or larva.

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Maternal effect gene

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A gene that, when mutant in the mother, results in a mutant phenotype in the offspring, regardless of the offspring’s genotype. Maternal effect genes, also called egg-polarity genes, were first identified in Drosophila melanogaster.

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Egg-polarity genes

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A gene that helps control the orientation (polarity) of the egg; also called a maternal effect gene.

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Bicoid

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A maternal effect gene that codes for a protein responsible for specifying the anterior end in Drosophila melanogaster.

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Morphogens

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A substance, such as Bicoid protein in Drosophila, that provides positional information in the form of a concentration gradient along an embryonic axis.

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Oncogenes

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A gene found in viral or cellular genomes that is involved in triggering molecular events that can lead to cancer.

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Proto-oncogenes

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A normal cellular gene that has the potential to become an oncogene.

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Tumor-suppressor genes

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A gene whose protein product inhibits cell division, thereby preventing the uncontrolled cell growth that contributes to cancer.

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Ras gene

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A gene that codes for Ras, a G protein that relays a growth signal from a growth factor receptor on the plasma membrane to a cascade of protein kinases, ultimately resulting in stimulation of the cell cycle.

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p53 gene

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A tumor-suppressor gene that codes for a specific transcription factor that promotes the synthesis of proteins that inhibit the
cell cycle.