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Encyclopedia > Eukaryotic transcription

Eukaryotic transcription is more complex than Prokaryotic transcription, because eukaryotes have evolved much more complex transcriptional regulatory mechanisms than prokaryotes. For instance, in eukaryotes the genetic material (DNA), and therefore transcription, is primarily localized to the nucleus, where it is separated from the cytoplasm (where translation occurs) by the nuclear membrane. DNA is also present in mitochondria in the cytoplasm and mitochondria utilize a specialized RNA polymerase for transcription. This allows for the temporal regulation of gene expression through the sequestration of the RNA in the nucleus, and allows for selective transport of RNAs to the cytoplasm, where the ribosomes reside. Kingdoms Animalia - Animals Fungi Plantae - Plants Protista Alternative Phylogeny Unikonta    Opisthokonta    Amoebozoa Bikonta    Apusozoa    Cabozoa       Rhizaria       Excavata    Corticata       Archaeplastida       Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms with a complex cell or cells, where the genetic material is organized into a membrane-bound nucleus or nuclei. ... Prokaryotes are unicellular (in rare cases, multicellular) organisms without a nucleus. ... The eukaryotic cell nucleus. ... Organelles. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... Organelles. ... Organelles. ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ...


The basal eukaryotic transcription complex includes the RNA polymerase and additional proteins that are necessary for correct initiation and elongation.

Contents

Initiation

The core promoter of protein-encoding genes also contains binding sites for the basal transcription complex and RNA polymerase II, and is normally within about 50 bases upstream of the transcription initiation site. Further transcriptional regulation is provided by upstream control elements (UCEs), usually present within about 200 bases upstream of the initiation site. The core promoter for Pol II often contains a TATA box, the highly conserved DNA recognition sequence for the TATA box binding protein, TBP, whose binding initiates transcription complex assembly at the promoter. A TATA box (also called Hogness box) is a DNA sequence (cis-element) found in the promoter region of most genes (it is considered to be a promoter sequence). ... Cartoon of the TATA binding protein structure. ...


Some genes also have enhancer elements that can be thousands of bases upstream or downstream of the transcription initiation site. Combinations of these upstream control elements and enhancers regulate and amplify the formation of the basal transcription complex. In genetics, an enhancer is a short region of DNA that can be bound with proteins (namely, the trans-acting factors, much like a set of transcription factors) to enhance transcription levels of genes (hence the name) in a gene-cluster. ...


Transcription process

Eukaryotes have three nuclear RNA polymerases, each with distinct roles and properties:[1][2]

These three RNA polymerases are commonly referred to as Pol I, Pol II and Pol III (and less often Pol A, Pol B, and Pol C, respectively). RNA polymerase I (also called Pol I) transcribes DNA to synthesize rRNA (Ribosomal RNA). ... The nucleolus is contained within the cell nucleus. ... A non-coding RNA (ncRNA) is any RNA molecule that functions without being translated into a protein. ... RNA polymerase II (also called RNAP II and Pol II) transcribes DNA to synthesize precursors of mRNA and most snRNA. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase. ... The interaction of mRNA in a eukaryote cell. ... RNA polymerase III (also called Pol III) transcribes DNA to synthesize ribosomal 5S rRNA, tRNA and other small RNAs. ... The nucleolus is contained within the cell nucleus. ... Similar to the cytoplasm of a cell, the nucleus contains nucleoplasm or nuclear sap. ... Transfer RNA (abbreviated tRNA) is a small RNA chain (74-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. ...


Transcription Regulation

The regulation of gene expression is an important aspect in organisms and rather complex in eukaryotes.[3] There are many ways a cell can regulate gene transcription and are different when prokaryotes are compared to eukaryotes. The goal though of gene expression is to control the rate and number of how many proteins are formed. Proteins are complex macromolecules and can be rather costly for cells to form on the fly and it is closely regulated by the cell to minimize waste. Gene modulation redirects here. ... A macromolecule is a large molecule with a large molecular mass bonded covalently, but generally the use of the term is restricted to polymers and molecules which structurally include polymers. ...


Gene expression in eukaryotes is also controlled by complex interactions between cis-acting elements within the regulatory regions of the DNA, and trans-acting factors that include transcription factors and the basal transcription complex. Gene expression, or simply expression, is the process by which a genes DNA sequence is converted into the structures and functions of a cell. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Protista Alternative Phylogeny Unikonta    Opisthokonta    Amoebozoa Bikonta    Apusozoa    Cabozoa       Rhizaria       Excavata    Corticata       Archaeplastida       Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms with a complex cell or cells, where the genetic material is organized into a membrane-bound nucleus or nuclei. ... Regulation has to be specific to particular genes. ... A Trans-acting factor is a molecule, generally a protein, whose task is to regulate another molecule, usually by binding to a cis-acting element. ... In molecular biology, a transcription factor is a protein that binds DNA at a specific promoter or enhancer region or site, where it regulates transcription. ...


Splicing

Also, splicing is an important aspect in the complex process of transcription in eukaryotes and can have a big influence in the final product. Ultimately this changes the mRNA message that is then translated into protein. Alternative splicing is one example of this and can easily change the proteins produced. It is currently thought now though that alternative splicing is now incorporated as much as 60% of human genetic coding. Meaning that a simple genetic code from a gene could potentially code for more then one protein. In genetics, splicing is a modification of genetic information prior to translation. ... Various modes of alternative splicing Alternative splicing is the process that occurs in eukaryotes in which the splicing process of a pre-mRNA transcribed from one gene can lead to different mature mRNA molecules and therefore to different proteins. ...


Primary (initial) mRNA transcripts in eukaryotic cells are synthesized as larger precursor RNAs that are processed by splicing out introns (non-coding sequences) and ligating exons (non-contiguous coding sequences) into the mature mRNA. Primary transcripts for some genes can be large. The primary transcripts of the neurexin genes, for instance, are as large as 1.7 megabases (1,700,000 bases), while the mature (processed) neurexin mRNAs are under 10 kilobases (10,000 bases), with as many as 24 exons and thousands of possible alternative splice variants that produce proteins with different activities. In genetics, splicing is a modification of genetic information after transcription, in which introns are removed and exons are joined. ... Diagram of the location of introns and exons within a gene. ... An exon is any region of DNA within a gene, that is transcribed to the final messenger RNA (mRNA) molecule, rather than being spliced out from the transcribed RNA molecule. ...


References

  1. ^ http://www.sparknotes.com/biology/molecular/dnatranscription/section3.rhtml
  2. ^ http://www.mun.ca/biochem/courses/3107/Lectures/Topics/euk_transcription.html
  3. ^ http://oregonstate.edu/instruction/bb492/lectures/RegulationII.html

 
 

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