Why does the golgi apparatus package

How is a vesicle formed during endocytosis? How are endocytosis and exocytosis similar? How are they different? Why is endocytosis important to cells? Is the white blood cells disposing of a worn-out red blood cell carried out through The researchers used immunoelectron microscopy to follow the pathway that rigid, nm, rod-shaped, procollagen trimers took through the Golgi in mammalian fibroblasts.

Luini and his colleagues observed procollagen only within Golgi cisternae, and never within the vesicles, which are normally much smaller et al. Other researchers, including Michael Melkonian and his colleagues, observed similar results when studying the Golgi apparatus of algae.

Several types of flagellated protists construct and export scales that attach to the cell surface of these organisms.

The scales have diverse but defined sizes and shapes. Researchers observed that in different species of algae that export both very large 1. The results from these diverse cell types support the cisternal maturation model of protein transport through the Golgi.

What were all the vesicles Rothman discovered doing in the Golgi? The current cisternal maturation model proposes that these vesicles are transport vehicles for Golgi enzymes rather than for protein cargo. Retrograde vesicles that travel backward through the Golgi bud off of a cisterna to transfer enzymes to younger cisternae.

Figure 3: Cisternal maturation in Golgi of Saccharomyces cerevisiae Golgi cisternae were labeled with dyes to track their movement over time in individual yeast cells. The cycling of red and green colors reflects the transient expression of different proteins at the cisternae surface.

Video courtesy of Dr. Benjamin S. Glick, University of Chicago. Today most Golgi researchers agree that the evidence favors the cisternal maturation model Emr et al. Evidence in support of this model came from the laboratories of Benjamin Glick and Akihiko Nakano, who concurrently performed experiments that strikingly demonstrated the process of cisternal maturation.

In a stunning visual assay, both labs used live-cell fluorescence microscopy to directly observe cisternal maturation in Golgi of Saccharomyces cerevisiae Baker's yeast Figure 3 Losev et al. The Golgi of S.

Instead of appearing as the typical stack of pita bread, in S. The individual cisternae are spread in an irregular manner throughout the cell. This unusual structure was ideal for using light microscopy to observe changes in the individual cisternae over time.

The vesicular transport model would predict that an individual cis cisterna would remain cis, with characteristic cis enzymes, over its entire lifespan. However, the cisternal maturation model would predict that a newly formed cis cisterna would eventually mature into a medial, then a trans cisterna, before breaking apart when its contents were packaged for their final destinations in the cell.

In their experiments the two research groups linked fluorescent proteins glowing green or red to the proteins present in different, individual cisternae of S. The researchers designed their experiments to test the predictions of the vesicular transport and cisternal maturation models.

If the vesicular transport model were correct, then the cisternae would be stable and maintain the same fluorescently labeled Golgi resident proteins over time. In contrast, if the cisternal maturation model was not correct, then each cisterna would contain a changing set of Golgi proteins over time.

In their experiments, the researchers created beautiful movies of the yeast and observed that the individual cisternae changed color over time. After analyzing a variety of Golgi proteins, the researchers consistently observed changes in the protein composition of individual cisternae over time. Their results provided strong evidence for the cisternal maturation model. Although researchers generally agree that the cisternal maturation model best fits the current data, there is still some debate over whether or not all cargo proteins take the same path.

Jennifer Lippincott-Swartz and her colleagues pioneered fluorescence methods to quantitatively measure the dynamics of cellular membranes, including the Golgi. Using these methods, they learned that some cargo proteins travel through the Golgi more slowly than the rates at which the cisternae mature Patterson et al. The researchers concluded that the cisternal maturation model could not accurately account for their data. While they do not dispute cisternal maturation, they additionally proposed a model whereby a two-phase system of membranes determines which cargo proteins and Golgi enzymes must distribute themselves during transport.

Complicating the situation further, at least some cell types have connections between different cisternae within the Golgi stack e. For example, Luini and colleagues observed intercisternal continuities during waves of protein traffic in mammalian cells Trucco et al. Many investigators will continue to investigate and refine these new models over time. While some aspects of protein transport through the Golgi are better understood than they used to be, there are still many unresolved issues surrounding the specifics within different organisms.

Moreover, questions remain about the unifying characteristics that are shared between all Golgi. A recent gathering of prominent Golgi researchers identified several important questions to be addressed in the future, including:. The structure of the Golgi apparatus varies in different cell types.

The dispersed nature of Golgi cisternae in the yeast Saccharomyces cerevisiae allowed researchers to resolve individual cisternae. By observing fluorescently labeled proteins that normal reside within different cisternae, researchers found convincing evidence that the Golgi cisternae change over time, supporting the cisternal maturation model of protein movement through the Golgi apparatus. However, there is clearly much left to discover about the Golgi.

Alberts, B. Molecular Biology of the Cell, 5th ed. New York: Garland Science, Becker, B. The secretory pathway of protists: Spatial and functional organization and evolution. Microbiological Reviews 60 , — Anterograde transport of algal scales through the Golgi complex is not mediated by vesicles. Trends in Cell Biology 5 , — doi: Bonfanti, L. Procollagen traverses the Golgi stack without leaving the lumen of cisternae: Evidence for cisternal maturation.

Those vesicles are actually made from the Golgi network. In fact, one of the functions of the Golgi is to make new vesicles out of the existing membrane of the Golgi and put into those vesicles the glycoproteins and other substances that are made in the Golgi network.

And then those vesicles, filled with the Golgi products, move to the rest of the cell, usually through the cell to the plasma membrane, which is their end destination. William Gahl, M. A more accepted idea is that chemicals being processed in the Golgi apparatus travel from one cisterna to another in transport vesicles or possibly along microtubules. Whatever the transport method, what is clear is that different chemical reactions take place in specially designated parts of the Golgi apparatus.

Golgi biochemicals. Where do they go? How do they get there? There are three main destinations for biochemicals released from the trans Golgi network: 1 inside the cell to the lysosomes; 2 the plasma membrane and 3 outside of the cell. In each case the destination is clearly linked to function. Using the food supermarket analogy, all the biochemicals transported away from the trans Golgi network have labels and barcodes built into them. They are all packed in vesicles and the construction of the vesicle or vessel is largely related to the vesicle contents, its destination and end use.

Animal cells contain many lysosomes and it is in these structures that some life expired organelles and other materials are digested see item CU9 about lysosomes. Vesicles containing biochemicals for continuous secretion flow to and fuse with the plasma membrane. This group of secretions will contribute to the biochemicals of the extracellular matrix, act as chemical signals to other cells, and provide proteins for the repair and replacement of the plasma membrane.

This constitutive or continuous secretory pathway is also the default pathway. Products from the Golgi apparatus not labelled for other routes use this line. They move from the trans Golgi network TGN towards the plasma membrane but accumulate in number before reaching the membrane. Certain triggers will make the vesicles fuse with the plasma membrane and release their contents in regulated bursts from the cell surface.

Insulin release is an example of this when it is triggered by a rise in blood glucose level.