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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