Sandbox 173: Difference between revisions
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There is positive enthalpy associated with the formation of Metarhodopsin II. This formation of the active state, also linked with the increase in entropy, is suggested to release the constraints in the helices and expose the cytoplasmic binding sites<ref name="Article9"/>. An important part of this process includes the 9-methyl group of retinal, which is suggested to provide a scaffold for proton transfers essential for the formation of the active state<ref name="Article9"/>. | There is positive enthalpy associated with the formation of Metarhodopsin II. This formation of the active state, also linked with the increase in entropy, is suggested to release the constraints in the helices and expose the cytoplasmic binding sites<ref name="Article9"/>. An important part of this process includes the 9-methyl group of retinal, which is suggested to provide a scaffold for proton transfers essential for the formation of the active state<ref name="Article9"/>. | ||
==== | ====Signaling Cascade and Polarization of the Cell Membrane==== | ||
[[image:RhodopsinTransducinComplex.jpg|thumb|left|Rhodopsin interaction with transducin.]] | [[image:RhodopsinTransducinComplex.jpg|thumb|left|Rhodopsin interaction with transducin.]] | ||
The excited rhodopsin interacts with a large number of transducin molecules, found in the cytoplasmic face of the disk membrane. Transducin is a member of the heterotrimeric GTP-binding proteins family, and it binds to GDP in the dark. This interaction generates a signaling cascade where transducin molecules are activated through the trigger of GDP-GTP nucleotide exchange in the α subunit<ref name="Article6"/>. Each activated transducin dissociates into Tα-GTP and Tβγ subunits, and Tα-GTP activates [http://en.wikipedia.org/wiki/CGMP-specific_phosphodiesterase_type_5 cGMP-specific phosphodiesterase] by binding and removing its inhibitory subunit<ref name="Textbook">Nelson, D., and Cox, M. Lehninger Principles of Biochemistry. 2008. 5th edition. W. H. Freeman and Company, New York, New York, USA. pp. 462-465.</ref>. | The excited rhodopsin interacts with a large number of transducin molecules, found in the cytoplasmic face of the disk membrane. Transducin is a member of the heterotrimeric GTP-binding proteins family, and it binds to GDP in the dark. This interaction generates a signaling cascade where transducin molecules are activated through the trigger of GDP-GTP nucleotide exchange in the α subunit<ref name="Article6"/>. Each activated transducin dissociates into Tα-GTP and Tβγ subunits, and Tα-GTP activates [http://en.wikipedia.org/wiki/CGMP-specific_phosphodiesterase_type_5 cGMP-specific phosphodiesterase] by binding and removing its inhibitory subunit<ref name="Textbook">Nelson, D., and Cox, M. Lehninger Principles of Biochemistry. 2008. 5th edition. W. H. Freeman and Company, New York, New York, USA. pp. 462-465.</ref>. | ||