Gene Regulation in Prokaryotes - plasmid, not protected by nuclear envelope - DNA is not bound up with histones -One of the best known pathways is the lac Operon

Lac Operon contains 1. a promoter (the specific nucleotide sequence tells a cell to begin transcription, RNA Polymerase binds here) 2. an operator (segment of DNA used to turn gene expression on or off, repressor protein binds here) 3. Three genes

Operation of the Lac Operon Lac Operon is turned OFF by the Repressor Protein – Binds with operator (segment of DNA) to prevent a gene from being transcribed. Lac Operon is turned ON by the presence of Lactose – Binds to repressor protein to prevent it from adhering to DNA so RNA Polymerase binds and begins transcription

Without Lactose:

With Lactose:

Eukaryotic Gene Regulation: Only a few of the available genes will be expressed in the cells of different tissues Complex!

Eukaryotic Gene Regulation: TATA box - repeating TATATATA’s signal that the gene is ahead!

Proteins that bind to enhancer sequences of a gene can work to: a.Open up tightly packed chromatin. b.Attract RNA polymerase. c. Block access to genes.

Fig. 14.9, p. 229 unit of transcription in a DNA strand exonintron mature mRNA transcript poly-A tail 5’ 3’ (snipped out) exon intron cap transcription into pre-mRNA 3’5’ RNA Editing

Hox genes

Development and Differentiation Hox genes are master control genes that control the differentiation of cells and tissues in the embryo. A mutation in hox gene in fruit flies had a leg growing where antenna should be.