[shininglight]

hi im having some trouble preparing for a lab on cell signalling and immunoblots! i have completed all the pre questions bar these two-i would be v.grateful if someone could help me out? 

discuss/speculate on methods to differentiate between post translationally modified proteins taking JNK as an example! 

which is more abundant in growth factorstimulated cells, serine/threonine or tyrosine phosphorylation,, why??? 

thanks

[Yggdrasil]

Here are some starting questions to consider:

How is JNK post-translationally modified?  How do people usually study this type of post-translational modification?

What are some growth factors?  What receptors do these growth factors stimulate?  How do these growth factor receptors function?

[shininglight]

well im not really sure, i think the answer is tyrosine as this  type of phosphorylation is of importance in cell signalling cascades of growth factors such as  EGF and IGF, receptor tyrosine kinases are the receptor types , but i don't know why it is tyrosine and not s/t phosphorylation?
and as for JNK i dont know how it is studied post translationally, but i guess a modification would be the attatchment of a phospahte group?? this is as much as i know,this will be my last post until this lab so any help would be great!

[Yggdrasil]

Yes.  Most growth factor receptors (EGFR, FGFR, etc.) are receptor tyrosine kinases.  As the name imply, these receptors transduce the extracellular stimulus of growth factor binding to an intracellular message, tyrosine phosphorylation.  Tyrosine kinases are different from serine/threonine kinases because of the different structures of tyrosine and serine/threonine side chains.  Whereas the OH on serine and threonine is relatively close to the backbone of the protein, the OH in tyrosine is more distant because of the aromatic ring.  The aromatic ring also slightly changes the properties of the OH (tyrosine's OH resembles a phenol whereas serine/threonine's OH resembles an alcohol).

JNK, like most mitogen-activated kinases (MAPKs), is phosphorylated.  So, you should look up methods to study protein phosphorylation.

[Equi]

I'd like to throw in that some growth-factor pathways in development include a lot of Ser/Thr kinase activity.