Molecular Basis of Transcriptional Regulation

what is differential gene expression?

- all cells have the same DNA but differ from each other: due to differential expression of genes

- some genes are transcribed in one type of cell, while different genes may be transcribed in the other

- the types of proteins present vary in different cell types

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

- can be controlled at multiple levels

what are cis-regulatory sequences?

- promoters and enhancers

- may be sequences

what are transcription factors?

- may bind to DNA at cis-regulatory sequences and control transcription

- general ones are important for carrying out transcription

- additional ones or repressors can control whether a gene expressed under specific conditions and at what level: transcription regulation

what is transcription regulation in bacteria?

- E. coli has a single circular DNA molecule

- codes for about 4300 proteins

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

- operons coordinately regulate transcription of clusters of genes

what is transcription regulation?

gene expression can be modulated by environmental factors

what is a tryptophan operon?

- has five genes that code for enzymes necessary for the production of the amino acid tryptophan, clustered together

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

- has a single promoter: has a tryptophan operator

what is a tryptophan operator?

- recognized by a protein called tryptophan repressor (transcription regulator)

- when bound to the active tryptophan repressor, it blocks access to RNA polymerase, preventing transcription (negative regulation)

what happens when tryptophan concentrations are low?

- the repressor does not bind to the operator (inactive)

- RNA polymerase can bind genes and transcribe them: on

what happens when tryptophan concentrations are high?

- tryptophan causes the repressor to change its conformation so that it binds to the operon, blocking RNA polymerase binding

- no transcription: off

what is 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 general transcription factors bind

- includes regions further upstream and sometimes downstream or within introns

what is the regulation of transcription in eukaryotes?

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

- transcription regulators bind to DNA and regulate gene expression

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

what is the complexity of gene regulation?

- transcriptional regulators themselves can be regulated

- can be regulated at various levels: expression of the gene that codes for them, translation of the protein, translocation of the protein into the nucleus