Biomembranes (3).pdf

# Topic 1 - Biomembranes (3).pdf ## Figure 14-1: Molecular Cell Biology, Sixth Edition This figure depicts the movement of proteins through the endomembrane system of a eukaryotic cell. **Exterior of the cell:** - **1:** Proteins enter the endoplasmic reticulum (ER) through a protein channel, a...

# Topic 1 - Biomembranes (3).pdf ## Figure 14-1: Molecular Cell Biology, Sixth Edition This figure depicts the movement of proteins through the endomembrane system of a eukaryotic cell. **Exterior of the cell:** - **1:** Proteins enter the endoplasmic reticulum (ER) through a protein channel, as they are being synthesized by ribosomes. This is called co-translational transport. - **2:** ER-to-Golgi vesicles bud off from the ER and fuse with the cis-Golgi network. - **3:** Retrograde Golgi-to-ER transport. **Golgi apparatus:** - **4:** Cisternal maturation: As proteins move through the Golgi, the cisternae mature and change their composition to modify the proteins. - **5:** Retrograde transport from later to earlier Golgi cisternae. **Cytosol:** - **6:** Constitutive secretion - proteins move through the Golgi and are transported to the cell exterior. - **7:** Regulated secretion - proteins are stored in secretory vesicles and are released from the cell in response to an external signal. **Plasma membrane:** - **8:** Sorting to lysosomes - proteins are transported to lysosomes or other organelles destined for degradation. - **9:** Endocytosis - the plasma membrane folds inward (invaginates) to bring in extracellular material. **Important details:** - The pathways shown in the figure indicate the movement of proteins through the endoplasmic reticulum (ER) and the Golgi apparatus. - The Golgi apparatus is divided into compartments, represented by stacked flattened sacs in the figure, which are distinct in their composition of resident proteins. - These organelles are linked to the ER and each other by vesicles, which are membrane-bound transport containers that bud off from the donor organelle and fuse with the acceptor organelle. - The figure indicates that there are specific transport pathways that move proteins in different directions. - The figure highlights the dynamic nature of biological membranes and the highly organized transport processes occurring within a living cell.