Lecture 18 - Regulation of Gene Expression

TRP operon

A type of polycistronic, repressible operon in which its product (tryptophan) inhibits its expression (expression is turned off)

What are two ways to stop transcription during regulation in prokaryotes?

1. Trp operon

2. Attenuation

How does the tryptophan operon work

1. Tryptophan binds to repressor

2. Repressor/tryptophan can bind operator and expression is turned off

Attenuation

An independent system to turn off expression

How does tryptophan attenuation work?

Translation of a small peptide STOPS transcription unless Trp is NOT available to complete the peptide

What happens if Trp is present?

Ribosome does NOT interfere with the formation of transcription termination loop

No enzymes made for synthesizing Trp (because it is already handled)

What happens if Trp is absent

Ribosome interferes with formation of transcription termination loop

Enzymes are made for synthesizing Trp (in order to compensate for Trp)

At what stage does regulation of gene expression happen in eukaryotes?

Transcriptional, but there are many levels of gene expression regulation

What are 4 transcription factors/regulations of gene expression in eukaryotes?

1. Gene expression regulated by interacting with the promoter region

2. Activators and repressors (similar to CAP and repressor in prokaryotes)

3. External environment influences

4. Differential gene expression leading to cell specialization in eukaryotes

Differential gene expression

Leads to cell specialization in eukaryotes (spatial and temporal regulation)

Gene duplication

The creation of new functions for genes through evolution without losing its old function

What are possible reasons for gene duplication?

1. Recombination errors

2. DNA replication errors

3. Transposition

4. viral integration into the genome