• Question: What is the exact transport mechanism by which proteins travel through the Golgi body?

    Asked by Frankie to vediacan, Laura on 19 Jun 2015.
    • Photo: Laura Newton

      Laura Newton answered on 19 Jun 2015:

      Hey Frankie!

      I’m sure you’ve seen pictures of the Golgi, it’s like a stack of little discs which are called cisternae, each disk has a phospholipd membrane around it. Newly made proteins arrive in little vesicles (spheres surrounded by phospholipid membranes that contain cytoplasm and the proteins) which fuse to the first stack and release their proteins into the middle of it. The proteins then start to be modified depending on what else they need attached to them.

      When they are done in the first disk, some of the membrane of the disc forms into a new vesicle and buds off from the membrane with the proteins inside. That vesicle then fuses with the membrane of the next disk and releases its proteins into it.

      There are different enzymes in each disk that can modify the protein in different ways so this fusing and budding keeps happening and the proteins move through the disks until eventually they have gone through all of them and then get sent wherever they are meant to be going in the cell.

      I hope this explains it ok, ask again if you have more questions or want more detail about it!

      Laura 🙂

    • Photo: Vedia Can

      Vedia Can answered on 22 Jun 2015:

      Hi Frankie!

      Sorry for the late reply!

      As Laura has mentioned 🙂 But here’s my attempt at explaining this process:
      The transport of proteins and lipids from Endoplasmic Reticulum to the Golgi apparatus and then to the cytosol and finally to the cell membrane is a complex process. But transport of these proteins through the Golgi body is relatively simple and occurs via one of the following transport mechanisms:
      1. Vesicular Transport – transport of the proteins via secretory vesicles (specifically the two organelles in tandem), with the help of COPI and COPII (coat proteins); they help in initiating the budding process/ membrane trafficking.
      2. Cisternal Maturation – cisternae can be viewed as transient carriers, the coated vesicles and others coming out of the ER can fuse together to form the cis cisternae. This slowly matures into a trans cisternae, which disintegrates into secretory vesicles (vesicles fuse together via homotypic fusion). So, the whole process is highly dynamic.
      3. Cisternal maturation with tubular transport – same as 2. with an exclusion of heterotypic fusion of vertically stacked cisternae. This accounts for the fused network.
      4. Rapid partitioning – This model assumes that the Golgi operates as a single compartment (remember vesicular transport, considers the Golgi as two compartments). The cargoes come in and fuse to the Golgi, partition and exit stochastically. This model matches the exponential kinetics of multiple secretory vesicles exiting from the Golgi.

      If you need a more detailed answer, google each of the mechanisms 🙂

      Best Wishes,

      Vedia

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