1. Gene Expression Activation of a gene to transcribe DNA into RNA.
Regulation of protein synthesis so proteins are not always being created, and only when needed
Gene expression is different for pro/eukaryotic cells.
Prokaryotes:
Operon – all genes associated with protein synthesis
Structural Gene – gene coding for a protein
Promoter -DNA section recognized by RNA Polymerase
Operator – DNA section that is the on/off switch
Operon Turned Off:
Regulator gene codes for a repressor protein to be made
Repressor attaches to DNA at the operator
RNA polymerase attaches to DNA at the promoter, but is blocked by the repressor

2. Gene Expression Operon Turned On:
Lactose binds to the repressor, changing its shape, releasing it from DNA
RNA polymerase reads the structural genes
Structural genes are then transcribed and translated to produce proteins
If lactose levels drop, repressor attaches to DNA again

3. Gene Expression Eukaryotes:
Enhancer – section of DNA which must be activated for transcription to occur
RNA polymerase binds to DNA at a promoter
Transcription factors bind to the enhancer and structural genes
Trans. factor on enhancer is the “activator”
A bend in the DNA brings the transcription factor to RNA polymerase to activate transcription.

4. Gene Expression After transcription, regulation of the gene continues…
During transcription, a pre-mRNA strand is made, which cannot be made into a protein.
The pre-mRNA contains repeating gene segments of:
Introns – non-coding part of RNA; removed
Exons – part of a gene that codes for protein; remain
Introns are removed from the pre-mRNA strand
Exons are spliced together
Translation into proteins can take place