Question

Using Figure 4.15, list the organelles of the endomembrane system and briefly describe their functions. 1. 2. 3. 4. 5. 6. Describe each of the parts of Figure 4.30.

Answer 1

The endomembrane system is crucial in the transportation of the proteins after they are synthesized to their desired location.

Different organelles work in unison to ensure this process. These organelles are:

1. Cytoplasm: Here, most of the proteins are synthesized.

2. Endoplasmic reticulum: The rough endoplasmic reticulum harbors ribosomes and therefore synthesizes proteins in its lumen. Here, the proteins are folded properly and checked for by the chaperones. Based on the localization signal, they are then packaged into appropriate vesicles.

3. Vesicles: These are the cargos for proteins. They package the proteins and transport them through the cytoplasm to their desired target which can be the nucleus, mitochondria, chloroplast, Golgi, cell membrane, etc.

4. Golgi: The proteins are transported from ER to the Golgi via vesicles. Here, they are post-translationally modified with appropriate modifications like glycosylation, SUMOylation, ubiquitylation, phosphorylation. These modifications are essential for the functionality of the protein. Again after they are modified, based on the localization signal present, they are packaged into vesicles and sent towards the target site.

5. Plasma membrane: Transmembrane proteins are delivered here. Vesicles dock and fuse with the membrane. In the process, the proteins are released and are embedded in the membrane. The proteins that are to be secreted out are also released outside the membrane by the fusion of the vesicles with the plasma membrane.

6. Lysosomes: Not all proteins are folded correctly. Hence, such proteins need to be degraded to ensure proper functioning of the cell. These proteins are sent to lysosomes where the pH is acidic and this results in the proteins being denatured.