Regulation of Gene Expression Eukaryotes

I. Regulation at Stages A. All organisms prokaryotes and eukaryotes alike have to regulate which genes are expressed. 1. both uni- and multicellular organisms must continually turn genes on and off in response to signals B. All cells have the same genome however, the genes expressed by each cell is unique allowing for cells to carry out specific functions. 1. Cells do not differ in genes present but differential gene expression

II. Eukaryotes Gene Expression A. To express a gene through protein synthesis there are several control points which gene expression can be turned on or off 1. The most common point is during transcription. Coming as a response to signals coming from outside the cell. 2. But it can be controlled along the structure of the chromosome, during initiation complex, RNA editing, attachment on ribosome, translation and protein processing.

III. Regulation of Chromatin Structure A. Along our cells our DNA is condensed into tightly packed chromatin made up of units called nucleosomes. 1. The location of a gene on the nucleosomes can affect how its expressed. B. Histones the proteins that DNA is wrapped around can allow some enzymes (transcription factors) to bind and allow access to genes. Depending on if the histone is acetylated – this causes histones to be loosely packed. If not acetylated chromosome is densely packed preventing the DNA from being read.

C. DNA methylation – regions of DNA that are usually not transcribed, inactivated genes due to the addition of the methyl groups. If they are removed DNA can then turn on these genes. D. Both DNA methylation & histone acetylation are examples of epigenetic inheritance traits transmitted by the mechanisms not directly involving the sequence.

IV. Regulation of Transcription Initiation A. There are several control elements that allow for transcription to occur including: 1. transcription factors 2. RNA polymerase 3. enhancers – affected by activators or repressors 4. mediated proteins B. The specific way when enhancers are activated (several different ways)are then folded along the DNA to mediated proteins which will interact with the promoter to help assemble the initial complex to start transcription.

Mediated proteins Transcription factors

V. Transcription Between the classes of cells A. Unlike prokaryotes that have all the genes for a specific function all located close together on an operon to be transcribed by one enzyme starting from one promoter site. B. Eukaryotes that are going to express several genes together (co-expressed) are scattered along several chromosomes. So several activators need to recognize the control elements along those chromosomes to allow for simultaneous transcription.

VI. Post-Transcriptional Regulation A. After transcription the mRNA can be alternatingly spliced changing which sections are treated as exons and introns by regulatory proteins.

VII. mRNA Degradation A. mRNA molecules in eukaryotes have a fairly long life span and can be translated several times before it is degraded.

VIII. Regulation of Translation A. Regulatory proteins can prevent mRNA from attaching correctly to the ribosome preventing translation. B. Protein factors can also activate or inactivate translation for ALL mRNA molecules in a cell at the same time.

IX. Regulation Along Protein Processing A. Some proteins in order to function properly need to undergo chemical modifications. Others have to be folded to begin working and still many proteins need to be transported to a specific location in the cell to begin functioning correctly. 1. At every point proteins can be regulated B. How long each protein functions can also be regulated by selective degradation. 1. Ubiquitin a small protein marks other proteins for degradation by proteasomes.