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BIOLOGY 2B03 (285)
Kim Dej (39)
Lecture 5

Lecture 5 Summary

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Kim Dej

Cell BioLecture 5 PostModification in Proteins GlycolysationAdding of carbohydratesPrimarily found in secretory protein or on the exoplasmic domain of membrane proteinsN linkedmost common form Addition of an ogliosaccharide to block the NH2 group from the Asn aa residue Olinkedaddition of 14 sugar residues on the OH group of SerThrAs polypep enters the ER lumenit is glycosylated by the addition of an ogliosaccharide as an intact unit to the asn aa from the lipid called dilichol FunctionsProtein foldingTransport Stability Celltocell adhesion and Cell identity FoldingAccelerated by ER resident proteins1 PDIs Protein Disulphide Isomerase2 Chaperones Hsc70 and BiP 3 Lectinsbinds to unfoldedmisfolded polypeptides carbohydrate adding onescalnexin4 Peptidylpropylisomerasemonitors rotation about the peptide bondPromotes reliable and rapid folding in proteins in the ER and the assembly of single subunits into multisubunitsProteolytic Cleaving of signalSecreted proteins and Type 1 integral membrane proteins signal Cleavagecleaved by signal peptidase Disulphide Bond interintra molecular disulphide bonds stabilize the tertiary and quartenary structures of a Formation protein oxidative linkages between SH groups on 2 cysteine aa residuesSpontaneously occurs in oxidizing environments ie the ER while the cyto is a reducing environProtein Disulphide IsomeraseAccelerates disulphide bond formation via 2 thiodisulphide transfer reactionsIts an ER resident protein It forms a disulphide bonded enzymesubstrate intermediate Start with substrateProtein with two SH groups bondedIn comes oxidizing enzyme with doubled bonded S Then an intermediate forms where this double S bond breaks and it is formed with the substrate Once a transfer of H ions occurs The enzyme is reduced with two SH attached and the substrate oxidizing with a horizontal disulphide bridge When 2 cysteines in close proximity to each other it is possible to create an incorrect vertical disulphide bond formation PDIs accelerates the rearrangement of this bond and corrects it to the right horizontal conform Unfolded Protein ResponseUnfolded proteins presentBiP dissociates with Ire1 and binds to unfolded proteinIre1 dimerizes forming an active endonuclease This endonuclease cleaves the Hac 1 mRNA and the HAC1 transcription factor is spliced and translated This HAC1 goes to the nucleus and upregulates the genes associated with the UPR response ie lectins PDIs chaperones etcWhy unfolded proteins in the first placeCells that make lots of secretory proteins need lots of chaperones
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