Regulation of Gene Activity

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

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.

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.

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.

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

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.

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.

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

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

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.

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

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