Gene Regulation 1: Prokaryotes (Genetics: Exam 2 Biology 1 UF)

Gene regulation

ensures that only certain genes are expressed in certain cells at

the correct time

Inducible genes

genes that are not expressed unless products are needed

(ex: genes the encode for lactose-digesting enzymes are only expressed if lactose is present)

Repressible genes

genes that are usually expressed unless products are not needed

(ex: genes that encode for the proteins used to synthesize tryptophan are always expressed until no more tryptophan is needed)

Constitutive genes

genes that are expressed nearly all of the time

(ex: genes that encode for tRNAs and ribosomes are essentially

always expressed)

Transcription factors

regulatory proteins that control gene activity

Repressors

transcription factor that prevents transcription

Activators

transcription factor that stimulates transcription

Lac operon

inducible series of genes that create products that break down lactose (turned on when lactose is present)

trp operon

repressible series of genes that create products used to synthesize tryptophan (turned off when enough tryptophan present)

Operon

A series of genes with a single promoter

Promoter

regulatory sequence on DNA that RNA polymerase binds

Activator

Regulatory proteins

Operator

a regulatory sequence between the promoter and the genes

Negative regulation

when the repressor blocks the RNA polymerase, preventing transcription

Positive regulation

When activators bind to a site near the promoter to stimulate

transcription of an operon

DNA-binding site

where transcription factors bind to target DNA

Allosteric site

where other molecules (like lactose or tryptophan) can bind

Allolactose

inducer that binds to repressor, changes repressor’s shape, can no longer bind to operator, genes for lactose metabolism enzymes are expressed

Inducer

Co-repressor

Inducible

repressible