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