Changes

'''TFIIE and TFIIH'''

'''TFIIE and TFIIH'''

After binding of the general transcirption machinery to the promoter, TFIIE and TFIIH assist Pol II in unwinding the DNA at the start site of transcription.  One of the subunits of TFIIH is a helicase responsible for the unwinding and TFIIE binds to and stablilizes the single stranded DNA.

After binding of the general transcription machinery to the promoter, TFIIE and TFIIH assist Pol II in unwinding the DNA at the start site of transcription.  One of the subunits of TFIIH is a helicase responsible for the unwinding and TFIIE binds to and stablilizes the single stranded DNA.

Another subunit of TFIIH contains a kinase activity responsible for phosphorylating the CTD region of Pol II.  Although this activity can be influenced by many factors, in simple systems it is believed to correlate with the initiation of transcription and that movement of RNA polymerase away from the promoter.

Another subunit of TFIIH contains a kinase activity responsible for phosphorylating the CTD region of Pol II.  Although this activity can be influenced by many factors, in simple systems it is believed to correlate with the initiation of transcription and that movement of RNA polymerase away from the promoter.

::# Release of polymerase from promoter

::# Release of polymerase from promoter

In prokaryotes, termination occures at discrete sites and translation can begin even before transcription has terminated.  In eukaryotes, transcription continues past the site where poly-A addition occurs and then terminates randomly (frequently 500 bases or so down stream).  RNA processing and splicing is completed in the nucleus before transported to the cytoplasm for translation.

In prokaryotes, termination occurs at discrete sites and translation can begin even before transcription has terminated.  In eukaryotes, transcription continues past the site where poly-A addition occurs and then terminates randomly (frequently 500 bases or so down stream).  RNA processing and splicing is completed in the nucleus before transported to the cytoplasm for translation.

==Translation==

==Translation==

mRNA is not a passive player in translation. It is a nucleic acid, and as such contains digital information that can target the mRNA to different parts of the cell, and has a secondary and tertiary structure that can attract the attentions of regulatory proteins.

mRNA is not a passive player in translation. It is a nucleic acid, and as such contains digital information that can target the mRNA to different parts of the cell, and has a secondary and tertiary structure that can attract the attentions of regulatory proteins.

In eukaryotes, even before mRNA leaves the nucleus, it is extensively modified from the pre-mRNA that was synthesised by RNA polymerase. mRNA is capped at its 5′ end and complexed to cap binding proteins. It is spliced by U-particles, which tag mRNA and the spliced out lariats with different hnRNPs: SR-rich proteins bind exons and hnRNPs bound to excised lariats package them up and mark them for destruction. The 3′ tail of mRNA has a poly-A tail added, which is bound by PABP. All this must occur before export factors binds, and all these items are required for appropriate export from the nucleus.

In eukaryotes, even before mRNA leaves the nucleus, it is extensively modified from the pre-mRNA that was synthesized by RNA polymerase. mRNA is capped at its 5′ end and complexed to cap binding proteins. It is spliced by U-particles, which tag mRNA and the spliced out lariats with different hnRNPs: SR-rich proteins bind exons and hnRNPs bound to excised lariats package them up and mark them for destruction. The 3′ tail of mRNA has a poly-A tail added, which is bound by PABP. All this must occur before export factors binds, and all these items are required for appropriate export from the nucleus.

[[Image:Mrna_export_ready.png|left|thumb|Export-ready RNA is really a ribonucleoprotein, with many associated proteins and RNPs.]]

[[Image:Mrna_export_ready.png|left|thumb|Export-ready RNA is really a ribonucleoprotein, with many associated proteins and RNPs.]]

Transcription reads the template DNA strand 3′→5′.  

Transcription reads the template DNA strand 3′→5′.  

RNA polymerase synthesises mRNA 5′→3′.  

RNA polymerase synthesizes mRNA 5′→3′.  

Translation reads the mRNA 5′→3′.  

Translation reads the mRNA 5′→3′.  

The ribosome synthesises protein NH3+ → COO−.  

The ribosome synthesizes protein NH3+ → COO−.  

It should be obvious, but note that the promoter is not the same thing as the start codon; nor is the RNA polymerase terminator the stop codon. There are generally untranslated regions (UTRs) at both ends of an RNA transcript, even in bacteria.

It should be obvious, but note that the promoter is not the same thing as the start codon; nor is the RNA polymerase terminator the stop codon. There are generally untranslated regions (UTRs) at both ends of an RNA transcript, even in bacteria.

With the G excised and UU inserted in the stretch.

With the G excised and UU inserted in the stretch.

== Bibliography ==  

== Bibliography ==  

*Stryer, Lubert. Biochemistry, 4th ed. New York: W. H. Freeman and Company, 1995

*Stryer, Lubert. Biochemistry, 4th ed. New York: W. H. Freeman and Company, 1995

*Tijian, Robert. "Molecular Machines that Control Genes." Scientific American 272 (1995): 54–61.

*Tijian, Robert. "Molecular Machines that Control Genes." Scientific American 272 (1995): 54–61.

==References==

==References==