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The cell

5. VESICULAR TRAFFIC

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Organelles are membrane bound cellular compartments.

Many organelles are communicated between each other by vesicles.

Vesicular traffic is used by many molecules, which are included in vesicles, to travel from a source organelle to a target organelle.

There two main vesicular paths. Secretion: starting in the endoplasmic reticulum and ending in the plasma membrane. Degradation: starting in the plasma membrane and finishing in lysosomes.

An eukaryotic cell may resemble a big city with several districts. Each of them is specialized in a particular role, such as energy production, manufacturing products, exportation, importation, communication with other cities, recycling, and many other. For this system to work properly, a rich and complex communication system is necessary between districts, which is carried out by transporters that go through different roads.

The cellular districts are the intracellular compartments and many of them are compartments delimited by a membrane, i.e. organelles. Each organelle is specialized in one or several function. For example, endoplasmic reticulum is in charge of synthesizing proteins for secretion and lipids for making membranes, Golgi complex produces carbohydrates to be attached to proteins and lipids, and is also a distribution center, lysosomes are in charge of degradation, mitochondria and chloroplasts synthesize ATP, etcetera.

Communication between some organelles is mediated by vesicles, which carry molecules both inside and as part of the vesicular membrane. Vesicular traffic is the name for all of these vesicular communication paths and the involved organelles. There are two main roads in this traffic map. One, which is known as secretory pathway, starts in the endoplasmic reticulum, which sends vesicles to the Golgi complex, and the vesicles from the Golgi complex are targeted to the cell membrane (exocytosis). The secretory pathway releases molecules into the extracellular space, and also carries molecules to the plasma membrane. The other pathway, which is an importing pathway, starts at the plasma membrane where vesicles and large compartments are originated by invagination (endocytosis). These vesicles fuse with the endosomes, which end up becoming lysosomes, where the incorporated molecules are degraded. It is a degradative pathway. There are other communication roads mediated by vesicles.

Vesicular traffic

Main pathways of communication mediated by vesicles between organelles. Roads and compartments constitute the vesicular traffic. Communication is usually bidirectional. No all the communication paths are depicted.

It is not yet fully demonstrated, but it would exist a bidireccional vesicular communication between organelles, i.e. if a source organelle sends vesicles to a target organelle, this last one will send back vesicles to the source organelle. For example, endoplasmic reticulum sends vesicles to the Golgi complex, which in turn send vesicles back to the reticulum. It is the same for the communication between plasma membrane and endosomes.

There are organelles, such as mitochondria, chloroplasts and peroxisomes, which are not part of the vesicular traffic because they do not send nor receive any vesicle. However, these organelles communicate with other organelles by other mechanisms, for example, by physical contacts of their membranes.


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Updated: 2016-05-17. 14:15