(S). Describe the process by which a cell surface glycoprotein is synthesized an
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(S). Describe the process by which a cell surface glycoprotein is synthesized and transported to the plasma membrane of the cell. (3 points) (6). What two post-translational modifications occur in the ER? (1 point) (7). Explain why the signal sequence used to target a protein to the nucleus (a signal patch) would not work for targeting a protein to the mitochondrion (an N-terminal sequence) and vice versa. Note: I'd like you to focus on the mechanism, not the exact amino acid sequence, which differs between the two.(2 points) (8). What is the fate of a vesicle lacking (a) v-SNAREs or (b) Rab? (1 points)Explanation / Answer
(5). The glycoproteins are synthesized firstly in the ribosome, then the oligosaccharides are added in the ER (O-linked oligosaccharides) or in the Golgi apparatus (N-linked oligosaccharides), then they are transportated into vesicles to the target memebrane.
(6). Protein folding and protein glycosylation of the of the O-linked oligosaccharides.
(7). The reason why a sequence that is used to target to the nucleus does not work to target a protein to the mitochondrion it is firstly because the sequence for each process is different, and this specific sequence allows the protein to interact with the component that wil translocate the protein in to the nucleus or into the mitochondrion.
Nucleus: the specific amino acid sequence binds to the nuclear import receptor protein (NIR), in the cytosol; then the complex protein-NIR interacts with a nuclear pore, which activates GTP reaction that results in a change of the configuration of the pore that allows the translocation of the protein-NIR into the nucleus and once it is there the complex dissociate and the NIR returns to the cytosol.
Mitochondrion: the specific amino acid sequence binds to the receptor in the mitochondrion, then complex receptor-protein diffuses within the membrane to a contact site, the protein is unfolded, moving across the membrane and then re-folded, all of this mediated by the protein transporter complex and its associated chaperons proteins.
(8a). The SNAREs proteins are important for the fusion of the vesicle with the target membrane, so a vesicle that lacks of its specific v-SNARE will not be available to fusion with the target membrane.
(8b). The Rab protein is important for the maduration and vesicular transport, if the vesicle lacks of this protein it is unable to get to the target membrane because it wil not interact with the SNAREs.
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