Gene Expression and Regulation

Study Notes

Gene expression is the process of using the information from a gene to create a functional product.
This product is usually a protein.
Non-protein coding genes like rRNA, tRNA, or snRNA create functional RNA.
Eukaryotes and prokaryotes use this process.

Adapting to environmental challenges requires altering gene expression.
Tissue-specific gene expression results from transcription control.
Hormones, heavy metals, and chemicals influence gene regulation.
Disease can result from the dysregulation of gene expression.
Positive and negative regulation are important.
A positive regulator (enhancer or activator) mediates positive regulation.
Inhibition of a negative regulator also results in positive regulation.
A negative regulator (silencer or repressor) mediates negative regulation.
An inducible gene's expression increases in response to an inducer or activator and has a low basal rate of transcription.
Genes with a high basal rate are downregulated by repressors and called repressible genes.

An operon is a cluster of structural genes that are expressed together, along with their promoter and operator.
The lac operon (lactose operon) is required for the transport and metabolism of lactose in Escherichia coli and other enteric bacteria.
It has three structural genes: lacZ, lacY, and lacA.

The lac operon enzymes are induced by the presence of lactose or isopropyl thiogalactoside (IPTG), a lactose analog.
When a bacterium is starved of a carbon source, it accumulates cAMP.
Glucose is the preferred carbohydrate source for E. coli.
When glucose is absent, the lac operon is turned on so the bacterium can metabolize alternative carbohydrates like lactose.
The lac operon promoter has two binding sites.
One site is where RNA polymerase binds.
The second is the binding site for the catabolite activator protein (CAP) and cyclic AMP (cAMP) complex.
This complex induces the lac operon enzymes.