bio lec - 8-11 PART 2 - Page 2 The ER is not only the place...

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Page 2 T he ER is not only the place to transfer the ptn into the vesicle but it also the place where the glycocilation take place so the modification which changes the properties of the ptn considerably Most of the glycocilation steps start in the ER there are only rare Eg in the cytocolic ptn. So here is the typical Eg of the modification found in the ptn which is translocated through the translocator into the lumen of the ER The ptn asp is linked to a glycoside tree And this is very complicated bec The series of event to build up this tree is not determine by the genetic directly “not by a series of nucleic acid” but it depend on a series of the glycocyle transferase acting on that residue
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Page 3 oligosaccharyl transferase , carries the completed tree from this lipid directly to the Asp and the remaining dolicholP is the carrier which is needed to build up the tree of complicated sugar residues so the glycoyilation is a cotransportation process : at the same time when the ptn is pushed through the translocator these trees are transferred to the asparagin residue The dolicholP is located in the ER mem To receive some mannose or Glu residue it has to be charged by these residues form the precursor which are normaly CP glucose or some thing like that - the phosphorelation step is needed first for dolichol “D” lead to D phosphoate - and then transfer of the UDP glucose residue is done leading to the D phosphate - then flipped to the inner part - then addition steps take place to build up this tree only understand the principle so the tree of this sugar residues are not constructed at the ptn but they are constricted on the lipid molecule and then they are transfer from the lipid molecule as a complete tree to the ptn and this is done on the asp residue
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Page 4 What is the impo about the glycosylation ???? Folding of the ptn is impo step controlled by the sugar residue transfer to the molecule And in the some part it is impo to have a glycosylation tree bec the excess proteases from the pancreases is prevented by a tree of glycocyl residue on the surface of the ptn
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bio lec - 8-11 PART 2 - Page 2 The ER is not only the place...

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