Summary

6. Proteins with an endoplasmic reticulum signal sequence are synthesized on the rough endoplasmic reticulum. The growing polypeptide chain is fed across the membrane as it is synthesized. The signal sequence may then be cleaved off.

7. The default pathway for proteins synthesized on the rough endoplasmic reticulum is to pass through the Golgi apparatus and be secreted from the cell via the constitutive pathway.

8. Glycosylation in the endoplasmic reticulum and then in the Golgi apparatus has two functions: to produce the final, functional form of the protein and to add further sorting signals such as the lysosomal sorting signal mannose-6-phosphate.

9. Vesicles shuttle between most of the single-membrane cellular organelles, the exception being peroxisomes. Budding and then fission of vesicles from the donor membrane can be driven by coatamer family proteins or by clathrin plus dynamin.

10. A tight association of vesicular and target SNARE proteins forces vesicles into close association with the target membrane. Fusion requires the action of a Rab family GTPase.

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