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Pre Initiation Complex

2018-10-25T16:09:47Z

170109781: Add content, links and some references

In [[Eukaryotes|eukaryotic]] [[Gene|gene]] expression the Pre Initiation Complex (PIC) mediates the binding between the [[Genome|genome]]'s promoter and [[RNA polymerase|RNA polymerase]]. Each type of RNA polymerase has a different PIC<ref>Cassimeris,L. et al., 2007; p219 Lewin's cells. 2nd ed. Sudbury: Jones and Bartlett.</ref>. Assembly of the PIC<ref>Sainsburys S, Bernecky C, Cramer P. Structural basis of transcription initiation by RNA polymerase II. Nature Review Molecular Cell Biology. 2015; 16:129-43.</ref> is required for initiating transcription. General transcription factors and RNA polymerase join together at the promoter, forming the PIC<ref>Lodish, H. (2016). Molecular cell biology. New York : W.H. Freeman Macmillan Learning. 2016.</ref>.

== Subunits ==

The complexity of PIC varies between the types of eukaryotic [[Rna polymerases in eukaryotes|RNA polymerase]]. For [[DNA polymerase I|polymerases I]] and [[Polymerase III|III]] the complex consists of only a few subunits.

For [[RNA polymerase II|polymerase II]] the PIC is far more complex. It consists of 6 [[General Transcription Factors|General Transcription Factors]] (GTF). [[TFIID|TFIID]] is the core recognition protein. It is made up of TATA binding protein (TBP) and TBP associated factor (TAF). TBP binds to the [[Tata box|TATA box]], initiating the assembly of PIC. [[TFIIA|TFIIA]] and [[TFIIB|TFIIB]] will then join. TFIIA stabilizes the binding complex while TFIIB helps recruit [[RNA_polymerase_II|RNA polymerase II]]. TFIIB interacts directly with [[RNA polymerase II|RNA polymerase II]] which has [[TFIIF|TFIIF]] attached to it. This allows [[TFIIE|TFIIE]] and finally [[TFIIH|TFIIH]] to bind. TFIIH has [[Helicase|helicase]] activity and starts seperating the strands at the start site, allowing the formation of an [[Open_complex|open complex]]. This process is known as promoter melting and it requires [[ATP hydrolysis|ATP-hydrolysis]]. TFIIH also contains one of the [[Kinase|kinases]] that phosphorylates the [[C-terminal domain|C-terminal domain]] (CTD) of RNA polymerase II. [[Phosphorylation|Phosphrylation]] of CTD is essential for the transition from intiation to elongation. When all GTFs and RNA polymerase II are recruited at the promoter, the assembly of PIC is complete.

However, initiating the assembly of PIC on a TATA-less promoter (promoter without TATA box but other core promoter elements) requires TAFs which responds to the activators. 

=== References ===

<references /><references /><references />

Chemotroph

2017-12-06T12:48:53Z

170109781: added and removed links, added text and references

An [[Organism|organism]] whose primary energy source is from chemical reactions. They obtain their energy by oxidising [[Organic compound|organic]] or [[Inorganic compound|inorganic compounds]]. They can also be known as chemoautotrophs and chemoheterotrophs<ref>Biology-online.org [internet] [cited 2015 Dec 2] Available from: http://www.biology-online.org/dictionary/Chemotroph</ref>.

==== Chemoautotrophs ====

Chemoautotrophs<ref>Gargaud M, Irvine W, Amils R, Cleaves H, Pinti D, Quintanilla J, Rouan D, Spohn T, Viso M and Tirard S. cyclopedia of astrobiology. 2nd Ed: Springer. 2015</ref> use inorganic carbon dioxide(CO2) as their carbon source. Chemolithographs are commonly known chemoautographs that use inorganic compounds such as ferrous iron, hydrogen, hydrogen sulfide, sulphur and ammonia to generate energy. All known chemoautotrophs are found to be prokaryotes that belongs to the [[Bacteria|bacteria ]]and [[Archaea|archaea ]]domains. They are found in extreme habitat such as deep sea vents and highly acidic environments. An example of a chemoautotroph is the ''Sulfolobus acidocaldarius'' found in highly acidic hot springs in US Yellowstone National Park<ref>Microbewiki. Sulfolobus acidocaldarius. 2010 [cited 6/12/17]; Available from: https://microbewiki.kenyon.edu/index.php/Sulfolobus_acidocaldarius</ref>.

==== Chemoheterotrophs ====

Chemoheterotrophs<ref>Gargaud M, Irvine W, Amils R, Cleaves H, Pinti D, Quintanilla J, Rouan D, Spohn T, Viso M and Tirard S. cyclopedia of astrobiology. 2nd Ed: Springer. 2015</ref> use reduced organic compounds as their energy and carbon source. It is usually known as [[Heterotroph|heterotrophs]]. 



=== References ===

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Oseltamivir

2017-12-05T00:21:53Z

170109781:

Oseltamivir is an [[Influenza|influenza]] [[Antiviral medication|antiviral medication]] which is taken orally. It is often sold under the brand name "Tamiflu"<ref>Omudhome Ogbru P. oseltamivir, Tamiflu: Drug Facts, Side Effects, and Dosing. MedicineNet. [cited 3 December 2017]. Available from: https://www.medicinenet.com/oseltamivir/article.htm</ref>.

It is a [[Neuraminidase|neuraminidase]] inhibitor<ref>PubChem. Oseltamivir. 2017 [cited 5/12/17];
Available from: https://pubchem.ncbi.nlm.nih.gov/compound/oseltamivir#section=Top</ref>. It blocks the [[Active site|active sites]] of neuraminidases, which are [[Enzyme|enzymes]] on the surface of influenza [[Viruses|viruses]] that cleave sialic acid, and prevents the viruses from entering the host cells. It also prevents the release of newly assembled influenza viruses from the host cells.

=== '''Structure of oseltamivir''' ===

=== [[Image:Structure of oseltamivir.png]] ===

Fig. 1: Structure of oseltamivir<ref>ChemIDplus. Oseltamivir. 2017 [cited 5/12/17];
Available from: https://chem.nlm.nih.gov/chemidplus/name/oseltamivir</ref>  

Oseltamivir is an acetamido cyclohexene and its structure is homologous to sialic acid.

Influenza viruses use sialic acid as receptors for entering the host cells. 

=== References ===

<references /><references /><references />

Oseltamivir

2017-12-05T00:21:01Z

170109781: Added text and reference

Oseltamivir is an [[Influenza|influenza]] [[Antiviral medication|antiviral medication]] which is taken orally. It is often sold under the brand name "Tamiflu"<ref>Omudhome Ogbru P. oseltamivir, Tamiflu: Drug Facts, Side Effects, and Dosing. MedicineNet. [cited 3 December 2017]. Available from: https://www.medicinenet.com/oseltamivir/article.htm</ref>.

It is a [[Neuraminidase|neuraminidase]] inhibitor<ref name="3">PubChem. Oseltamivir. 2017 [cited 5/12/17];
Available from: https://pubchem.ncbi.nlm.nih.gov/compound/oseltamivir#section=Top</ref>. It blocks the [[Active_site|active sites]] of neuraminidases, which are [[Enzyme|enzymes]] on the surface of influenza [[Viruses|viruses]] that cleave sialic acid, and prevents the viruses from entering the host cells. It also prevents the release of newly assembled influenza viruses from the host cells.

=== '''Structure of oseltamivir''' ===

=== [[Image:Structure_of_oseltamivir.png]] ===

Fig. 1: Structure of oseltamivir<ref name="2">ChemIDplus. Oseltamivir. 2017 [cited 5/12/17];
Available from: https://chem.nlm.nih.gov/chemidplus/name/oseltamivir</ref> 

Oseltamivir is an acetamido cyclohexene and its structure is homologous to sialic acid.

Influenza viruses use sialic acid as receptors for entering the host cells. 

=== References ===

<references /><references /><references />

File:Structure of oseltamivir.png

2017-12-04T23:55:35Z

170109781: Structure of oseltamivir

Structure of oseltamivir