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.