Bio 20A, Chapter 16., Regulation Of Gene Expression

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virus

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Any of a group of ultramicroscopic particles constructed of nucleic acid and protein (and, sometimes, lipid) that require living cells in order to reproduce. Viruses evolved multiple times from different cellular species

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virion

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The virus particle, the minimum unit capable of infecting a cell

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negative regulation

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A type of regulation in which a gene is normally transcribed, and the binding of a repressor protein to the promoter prevents transcription.

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positive regulation

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A form of gene regulation in which a regulatory macromolecule is needed to turn on the transcription of a structural gene; in its absence, transcription will not occur

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lytic cycle

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A viral reproductive cycle in which the virus takes over a host cell's synthetic machinery to replicate itself, then bursts (lyses) the host cell, releasing the new virus

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bacteriophage

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Any of a group of viruses that infect bacteria. Also called phage.

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capsids

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The outer shell of a virus that encloses its nucleic acid

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transduction

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Transfer of genes from one bacterium to another by bacteriophage

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lysogeny

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A form of viral replication in which the virus becomes incorporated into the host chromosome and remains inactive. Also called a lysogenic cycle.

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prophage

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The noninfectious units that are linked with the chromosomes of the host bacteria and multiply with them but do not cause dissolution of the cell. Prophage can later enter into the lytic phase to complete the virus life cycle.

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retorovirus

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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 host cell

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enveloped virus

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A virus enclosed within a phospholipid membrane derived from its host cell

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reverse transcriptase

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An enzyme that catalyzes the production of DNA (cDNA), using RNA as a template; essential to the reproduction of retroviruses

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provirus

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Double-stranded DNA made by a virus that is integrated into the host's chromosome and contains promoters that are recognized by the host cell's transcription apperatus

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inducer

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A compound that stimulates the synthesis of a protein

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inducible

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Produced only in the presence of a particular compound or under particular circumstances.

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constitutive

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Always present; produced continually at a constant rate

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structural gene

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A gene that encodes the primary structure of a protein not involved in the regulation of gene expression

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operon

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A genetic unit of transcription, typically consisting of several structural genes that are transcribed together; the operon contains at least two control regions: the promoter and the operator

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operator

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The region of an operon that acts as the binding site for the repressor

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repressor

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A protein encoded by a regulatory gene that can bind to a specific operator and prevent transcription of the operon

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regulatory gene

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A gene that codes for a protein (or RNA) that in turn controls the expression of another gene

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catabolite repression

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In the presence of abundant glucose, the diminished synthesis of catabolic enzymes for other energy sources

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restriction site

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A specific DNA base sequence that is recognized and acted on by a restriction endonuclease

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TATA box

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An eight-base-pair sequence, found about 25 pairs before the starting point for transcription in many eukaryotic promoters, that binds a transcription factor and thus helps initiate transcription

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transcription factors

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The synthesis of RNA using one strand of DNA as a template

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structural motifs

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A three-dimensional structural element that is part of a larger molecule. For example, there are four common motifs in DNA-binding proteins: helix-turn-helix, zinc finger, leucine zipper, and helix-loop-helix

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epigenetics

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The scientific study of changes in the expression of a gene or set of genes that occur without change in the DNA sequence

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methylation

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The addition of a methyl group (--CH3) to a molecule

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CpG islands

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DNA regions rich in C resides adjacent to G residues. Especially abundant in promoters, these regions are where methylation of cytosine usually occurs

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demethylase

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An enzyme that catalyzes the removal of the methyl group from cytosine, reversing DNA methylation

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genomic imprinting

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The form of a gene's expression is determined by parental sources (ie.e, whether the gene is inherited from the male or female parent)

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interference RNA

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(RNAi) A mechanism for reducing mRNA translation whereby a double-stranded RNA, made by the cell or synthetically, is processed into a small, single-stranded RNA< whose binding to a target mRNA results in the latter's breakdown

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alternative splicing

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A process for generating different mature mRNAs from a single gene by splicing together different sets of exons during RNA processing

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microRNA

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A small, noncoding RNA molecule, typically about 21 bases long, that binds to mRNA to inihibit its translation

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ubiquitin

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A small protein that is covalently linked to other cellular proteins identified for breakdown by the proteosome

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proteasome

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In the eukaryotic cytoplasm, a huge protein structure that binds to and digests cellular proteins that have been tagged by ubiquitin