Eukaryotic gene organization and expression

 Eukaryotes fall into two major groups: unicellular organisms and multicellular organisms. In both eukaryotes groups the control of gene expression is more complicated than is in the case with prokaryotes  there are number of levels at which gene expression can be regulated in eukaryotes.

 Levels of control of gene expression:

Gene expression  in eukaryotes is regulated at a number of distinct levels. Regulatory systems have been found for:

1. The control of transcription

2. of precursor RNA processing

3. of transport of the mature RNA out of the nucleus

4. of translation of the mRNAs

5. of degradation of the mature RNAs

6. of degradation of the protein products

                   The control of transcription itself involves a number of elements. At the DNA level, transcription of protein –coding genes involves the interaction of transcription factors with promoter elements and of regulatory proteins with both promoter elements and enhancer elements. Depending on the element and the protein that binds to it, the effect on transcription may be positive or negative .Activation of transcription through proteins binding at the distinct enhancer elements is thought to involve a looping of the DNA, brought about by interaction of the regulatory proteins bound at the enhancer and promoter elements.

 Transcriptional control

 transcription control

           General aspects of transcriptional control. Transcriptional control regulates whether or not a gene is to be transcribed and the rate at which transcripts are produced.eukayotic genes that are protein-coding contain both promoter elements and enhancers. The promoter elements are found just upstream of the transcription initiation site, while the enhancers are usually some distance away, usually much farther upstream. Promoter elements as modulated the function in regulation of expression of the gene with which they are associated.Certain promoter elements, such as the TATA elements, are required for transcription to begin. Other promoter elements function to determine whether or not transcription of the gene