Gene Regulation: Operons, Repressors, and Activators in Molecular Biology

Operator

the on and off signal for gene expression

Operon

entire stretch of DNA that includes the operator, promoter and the genes they control.

Repressor

protein that turns off gene expression

Regulatory gene

gene that codes for the repressor

Corepressor

molecule that cooperates with a repressor protein to switch the operon off

Inducer

inactivates a repressor to turn the operon on

Activator

stimulatory protein that turns on expression

Cyclic AMP (cAMP)

a molecule that binds CRP to help activate transcription in the lac operon

Differential gene expression

the expression of different genes by cells with the same genome

Histone acetylation

when acetyl groups are attached to the histone tail

DNA methylation

the addition of methyl groups to certain bases in DNA and is associated with reduced transcription

Epigenetic inheritance

the inheritance of traits by mechanisms not directly involving nucleotide sequence (ie alteration of DNA)

Control elements

segments of noncoding DNA that serve as binding sites for transcription factors that help regulate genes in eukaryotes

Enhancers

groups of distal (long range) control elements

MicroRNAs

small, single-stranded RNA molecules that can bind complementary sequences in mRNA

Small interfering RNAs (siRNAs)

RNA downregulates gene expression

RNA interference (RNAi)

the process of blocking gene expression by siRNAs

Long noncoding RNAs (lncRNAs)

an extended RNA that regulates mRNA expression

Differentiation

the process by which cells become specialized in structure and function

Morphogenesis

the sum of the physical processes that give an organism its shape

Cytoplasmic determinants

maternal substances in the egg that influence early development

Induction

when signal molecules from embryonic cells cause changes in nearby target cells

Determination

irreversibly commits a cell to becoming a particular cell type

Pattern formation

the development of a spatial organization of tissues and organs

Positional information

the molecular cues that control pattern formation, tells a cell its location relative to the body axes and to neighboring cells

Homeotic genes

control pattern formation in the late embryo, larva and adult stages

Embryonic lethals

mutations that cause death during embryogenesis

Maternal effect genes

genes that encode cytoplasmic determinates that initially establish the axes of the body of fruit flies (Drosophila)

Bicoid

a type of maternal effect gene that affects the front half of the body

Morphogens

a substance that helps to establish an embryo's axes and other features of its form

Oncogenes

mutations in genes that code for proteins that stimulate normal cell growth and division

Proto-oncogenes

the genes that get altered to form cancer cells

Tumor-suppressor genes

normally inhibit cell division

Ras gene

a G protein that relays a signal from growth factor receptor on the cell surface

P53 gene

suppress the cell cycle, activates cell suicide genes