Ch 11 – Gene Expression The control of a gene at transcription, translation for even the polypeptide.

Prokaryotes (Bacteria) Operons – control of transcription These comprise of a structural gene, operator and promoter. Promoter region organizes RNA polymerase and starts transcription. Operator region is binding site for a repressor protein. This protein will stop RNA polymerase from binding.

Also involved is a regulator gene that codes for that repressor protein. These proteins have binding sites for a particular molecule. The binding of that molecule will make the repressor protein release from the operator.

Example from the book (lac operon) Repressor protein is attached to operator. Lactose will bind to the repressor protein causing it to release from the operator and transcription begins. The protein formed is a lactose metabolizing protein. It is important to control the production of protein until they are needed. Why? Energy (ATP)

Eukaryotes use different systems 1. Control of transcription In eukaryotic cells, RNA polymerase need transcription factors to attach RNA polymerase to the promoter region on the DNA. These factors can “hold” RNA polymerase ready to transcribe a gene. “Up stream” of the promoter and structural gene is the enhancer region. Other transcription factors bind here and act as activators.

When the DNA is bent by bending proteins the transcription factors are brought together and the RNA polymerase is allowed to transcribe the structural gene.

2. Control after translation The mRNA (pre-mRNA) is made up of exons and introns. Exon (EXpressed) are translated into proteins. Introns (INtervening) are removed and not translated. The introns are removed, the exons assembled together and the new mRNA is translated.

3. Epigenetics The control of genes form outside “on top” of the genome. Environmental conditions can change the function of your DNA by changing your epigenome (and your offspring). Methyl groups can be added to cytosines and adenines turning off the gene. (This could be good or bad) Tight coiling of areas of DNA prohibit the promoter region being accessed and thus stopping transcription of the gene. Histones

4. Homeotic Genes Regulatory genes that control the pattern of body formation during early development. legs, wings, body segments, etc.

5. Protein Modification Modification of proteins Insulin