Chapter 19 Flashcards
A gene that must be expressed continually for the cell to survive.
housekeeping gene
The continual expression of a gene.
constitutive gene expression:
The conditional expression of a gene based on the cellular need for the gene product, achieved by the presence or absence of activators, repressors, enhancers, and other regulatory factors.
regulated gene expression
The positive regulation of the expression of a gene or genes.
activation
A decrease in the expression of a gene in response to a change in the activity of a regulatory protein.
repression
In eukaryotes, a protein that affects the regulation and transcription initiation of a gene by binding to a regulatory sequence near or within the gene and interacting with RNA polymerase and/or other transcription factors.
transcription factor
(1) A DNA-binding protein that positively regulates the expression of one or more genes; that is, transcription rates increase when an activator is bound to the DNA.
(2) A positive modulator of an allosteric enzyme.
activator
A protein that binds to the regulatory sequence or operator for a gene, blocking its transcription.
repressor
A DNA sequence involved in regulating the expression of a gene; for example, a promoter or operator. Also called a regulatory site.
regulatory sequence
The increased expression of a gene by the binding of an activator protein.
positive regulation
The decreased expression of a gene due to the binding of a repressor protein.
negative regulation
The characteristic of an enzyme or other protein in which binding of the first molecule of a ligand changes the affinity for the second molecule. In positive cooperativity, the affinity for the second ligand molecule increases; in negative cooperativity, it decreases.
cooperativity
The interaction of proteins bound at distant sites on a DNA molecule so that the intervening DNA forms a loop.
DNA looping
A DNA sequence that facilitates the expression of a given gene; it may be located a few hundred, or even thousand, base pairs away from the gene. In yeast, enhancers are called upstream activator sequences (UASs).
enhancer
A protein that stimulates transcription by binding both the RNA polymerase and an activator or activators, without binding the DNA directly.
coactivator
A protein that inhibits transcription by binding both the RNA polymerase and a repressor or repressors, without binding the DNA directly.
corepressor
A short sequence of DNA that prevents inappropriate cross-signaling between regulatory elements for different genes. Also called a boundary element.
insulator
The control of gene expression by the net effect of multiple, sometimes conflicting, regulatory signals.
signal integration
A region of DNA that interacts with a repressor protein to control the expression of a group of genes organized in an operon.
operator
A small molecule that binds a transcription activator or repressor, causing a conformational change in the regulatory protein that results in an increase or decrease in transcription from the gene.
effector
A contiguous mRNA with more than two genes that can be translated into proteins.
polycistronic mRNA:
A unit of genetic expression consisting of one or more cotranscribed genes and the operator and promoter sequences that regulate their transcription.
operon
A group of genes or operons that are coordinately regulated even though some, or all, may be spatially distant in the chromosome or genome.
regulon
The use of specific combinations of a limited number of regulatory proteins to exert fine control over gene expression.
combinatorial control
The α helix in a DNA regulatory protein that recognizes and binds to the DNA regulatory site.
recognition helix
A sequence that is the reversed complement of a downstream sequence.
inverted repeat
A supersecondary protein motif consisting of two α helices separated by a β turn. This motif is crucial to the interaction of many bacterial regulatory proteins with DNA.
helix-turn-helix motif:
A conserved 60 amino acid sequence motif in transcription activators encoded by genes that regulate body pattern development.
homeodomain motif
A leucine zipper motif in which one side of the recognition helix has a series of basic residues, which facilitates DNA binding.
basic leucine zipper motif:
A protein structural motif involved in DNA recognition by some DNA-binding proteins; characterized by a single atom of zinc coordinated to four Cys residues or to two His and two Cys residues.
zinc finger motif:
A class of small RNA molecules (21 to 23 nucleotides after processing is complete) involved in gene silencing by inhibiting translation and/or promoting the degradation of particular mRNAs.
microRNA (miRNA):
Methods of gene silencing, mediated by short interfering RNAs (siRNAs) or microRNAs (miRNAs), which bind to and silence the mRNA transcript, usually by targeting it for degradation. MicroRNAs are endogenous to the cell, produced by nucleases from longer transcripts encoded in the genome; siRNAs are generated by the same cellular enzymes from exogenous double-stranded RNA, introduced into the cell by viral infection or experimental manipulation.
RNA interference (RNAi):
A large assembly of enzymatic complexes that function in the degradation of damaged or unneeded cellular proteins. In eukaryotes, also called a 26S proteasome.
proteasome
