Molecular Basis of Transcription Regulation (L15)

differential gene expression

-all cells have the same DNA but differ vastly from each other

-different cell types have very different characteristics, even if they come from the same individual and have the same genetic code

-some genes are transcribed in one type of cell while other genes may be transcribed in another

-gene expression differs in different types of cells

-external signals can lead to changes in gene expression under different conditions

cis-regulatory sequences

-promoters and enhancers

-transcription factors may bind to DNA and control transcription

-additional transcription factors can control whether a gene is expressed under specific conditions --> transcription regulation

bacteria

-E. coli has a single circular DNA molecule that codes for about 4300 proteins

-only some of the genes are turned on at any given time

-transcription regulation: gene expression can be modulated by environmental factors

transcription regulation in bacteria

-operons coordinately regulate the transcription of clusters of genes

-ex: 5 genes that code for enzymes that are necessary for the production of tryptophan are clustered together on the tryptophan operon

-the genes on the operon are all transcribed when tryptophan concentrations in the environment are low

tryptophan operon (trp operon)

-has a single promoter

-contains a tryptophan operator within the promoter

-tryptophan operator is recognized by a tryptophan repressor

-active tryptophan repressor binds the operator --> blocks access to RNA polymerase --> prevents transcription (negative regulation)

low tryptophan concentration

-the repressor does not bind to the operator

-RNA polymerase can bind

-genes are transcribed

-operon on

high tryptophan levels

-tryptophan causes the repressor to change its conformation so it binds to the operon

-RNA polymerase binding is blocked

-no transcription

-operon off

the gene control region in eukaryotes

-refers to the whole region of DNA involved in controlling the expression of the gene

-includes the promoter region where transcriptional factors bind and regions further upstream

-sometimes includes regions downstream or within introns

-proteins that bind to these different regions of DNA can often interact with each other

transcription regulation in eukaryotes

-transcription factors bind to DNA and regulate gene expression

-co-activators and co-repressors play a role in regulating gene expression, often without binding to DNA directly

-co-activators activate transcription --> gene on

-co-repressors repress transcription --> gene off

combinations of transcription activators

can act synergistically

regulation of transcription regulators/factors

-expression of the gene that encodes for them

-translation of the protein

-translocation of the protein into the nucleus

In bacteria, what is the primary function of the operon?

To regulate the expression of a group of functionally related genes

3 multiple choice options