Regulation of Gene Activity

1. Regulation of Gene Activity

2. Conservation • Remember, our bodies are conservative, they only make what we need, when we need it. • How do they know this???

3. Operon • Jacob and Monod – E. coli – capable of regulating the expression of its genes • Regulator gene – codes for repressor • Repressor – controls whether the operon is active or not.

4. Operon • Promoter - DNA, beginning of gene to be transcribed, signals the start of a gene • Operator – portion of DNA where repressor binds, controls mRNA synthesis • When repressor binds here, RNA polymerase cannot attach to the promoter, prevents transcription • Structural genes – codes for primary structure of enzyme to be transcribed.

5. trp operon • Exist in “on” position – repressible • Products – 5 different enzymes, synthesis of AA tryptophan • If tryptophan is already present, it binds to repressor, which then binds to operator and no transcription takes place.

6. lac operon • Makes 3 enzymes needed for metabolism of lactose • When lactose is present, it binds to the repressor, and repressor cannot bind to operator, therefore transcription takes place • Lactose is an inducer, inducible operon

7. Eukaryotic regulation • 5 primary levels of control • Chromatin structure • Transcriptional control: transcriptional factors initiate/regulate transcription • Posttranscriptional control: mRNA processing and how fast mRNA leaves the nucleus • Translational control: when translation begins and how long it continues • Posttranslational control: after protein synthesis, polypeptide may have to undergo additional changes before it is functional.

8. Chromatin structure • Levels of chromatin organization is related to the degree that the nucleosomes coil. • Heterochromatin – highly condensed chromatin, inactive • Barr Body- only in females, small, dark, condensed chromatin, inactive X chromosome • Euchromatin – loosely compacted chromatin, potentially active, genes expressed.

9. Chromatic regulation • Chemical modifications to the histones and DNA can influence chromatin structure and gene expression • Histone acetylation – histone tails, with enzymes, catalyze the addition or removal of specific chemical groups, like acetyl, methyl and phosphate groups. • Opens up the chromatin structure and makes it accessible for transcription • Adding methyl groups to tails condenses the DNA

11. DNA Methylation • Methylate certain bases on DNA • Seen in plants, fungus and animals • Genes that are not expressed are usually more methylated • Removing methyl groups can turn on genes and this can be passed on. • Seen in X inactivation

12. Epigenetic Inheritance(histone acetylation and DNA methylation) • Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence. • Modifications to chromatin can be reversed while mutations are permanent. • May answer question to why identical twins can have different diseases.

13. Transcription regulation • Involves proteins binding to DNA and either facilitate or inhibit binding of RNA polymerase. • Transcription factors – essential for the transcription of all protein-coding genes. • Enhancers – downstream from promoter • Figure 15.10

14. Post- transcriptional regulation • RNA processing • Translational control – Initiation, elongation, termination on ribosome • Post translational control – after protein is made, before it is activiated.