DICTYOSOMES: STRUCTURE AND FUNCTIONS - BIOLOGY - 2024

The dictyosomes are membranous sacs stacked considered the fundamental structural unit of the Golgi apparatus. The set of dictyosomes, with associated vesicles and tubule network, constitute the Golgi complex. Each dictyosome can be made up of several saccules, and all dictyosomes in the cell constitute the Golgi complex.

Among the most prominent membranous organelles of the cell is the Golgi complex. This has a rather complex structure similar to several flat bags stacked on top of each other.

Although in animal cells they tend to be stacked, in plants, the dictyosomes are distributed throughout the cell. For this reason, what we understand as Golgi is a construction that we make of the first, because in plant cells we see dichthyosomes but it does not seem that we see Golgi.

As the cell prepares to divide, however, the stacked-sac structure disappears and a tubular one becomes more apparent. These remain dichthyosomes.

For some it does not make sense to separate Golgi dichthyosomes as distinct signifiers. However, as they represent different levels of structural complexity, it is preferable to maintain the distinction between them. A rung does not make a ladder, but neither does it exist without those.

Golgi dichthyosomes present a polarity dictated by the orientation of the membranes towards the nucleus (cis face) or contrary to it (trans face). This is important to fulfill its function as an organelle in charge of the storage, trafficking and final location of proteins in the cell.

Structure of dictyosomes

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The architecture of the dichthyosomes, and therefore of the Golgi, is highly dynamic. This means that it changes depending on the division stage of the cell, the responses it gives to environmental conditions, or its state of differentiation.

Recent studies indicate that dictyosomes can not only be seen as flattened saccules or as tubules. There may be at least 10 different forms of dictyosomes.

With few exceptions, dichthyosomes thus consist of ovoid membranous sacs, predominantly in the form of cisternae stacked in Golgi in cis. In Golgi in trans, on the contrary, tubular forms predominate.

In any case, in animal cells, the saccules are connected to each other by a tubular network that allows them to be held together forming conspicuous ribbons.

In plant cells, the organization is diffuse. In both cases, however, the dictyosomes are always adjacent to the exit sites of the endoplasmic reticulum.

Animal cells

In general, the dictyosome (Golgi) ribbons in an interphase animal cell are located between the nucleus and the centrosome. When the cell divides, the ribbons disappear, as they are replaced by tubules and vesicles.

All these changes in structure and location are controlled in animal cells by microtubules. In the diffuse dichthyosomes of plants, by actin.

When mitosis is complete and two new cells are generated, they will have the Golgi structure of the mother cell. In other words, dictyosomes have the ability to self-assemble and self-organize.

The Golgi macrostructure in animal cells, particularly forming a ribbon of saccules, appears to function as a negative regulator of autophagy.

In autophagy, the controlled destruction of internal cellular content helps regulate development and differentiation, among other things. The structure of tape dichthyosomes under normal conditions helps to control this process.

Perhaps for this reason, when its structure is disturbed, the resulting lack of control can manifest itself in neurodegenerative diseases in higher animals.

Function

The Golgi complex functions as the distribution center of the cell. It receives peptides from the endoplasmic reticulum, modifies them, packages them, and ships them to their final destination. It is the organelle in which the secretory, lysosomal and exo / endocytic pathways of the cell also converge.

The cargo from the endoplasmic reticulum reaches the Golgi (cis) as vesicles that fuse to it. Once in the lumen of the cistern, the contents of the gallbladder may be released.

Otherwise, it will continue its course to the trans face of Golgi. In a complementary way, Golgi can give rise to vesicles of different functions: exocytic, secretory or lysosomal.

Post-translational modification of some proteins

Among the functions of this structure is the post-translational modification of some proteins, particularly by glycosylation. The addition of sugars to some proteins account for their functionality or cell fate.

Protein and carbohydrate phosphorylation

Other modifications include the phosphorylation of proteins and carbohydrates, and other more specific ones that determine the final fate of the protein. That is, a mark / signal that indicates where the protein must go to exert its structural or catalytic function.

Secretory pathways

Golgi processing pathways can converge. For example, for many proteins present in the cell matrix, both post-translational modification and targeting of their deposition must occur.

Both tasks are carried out by Golgi. It modifies these proteins by adding glycosaminoglycan residues, and then exports them to the cell matrix by means of particular vesicles.

Connection with lysosomes

Structurally and functionally, Golgi is connected with lysosomes. These are membranous cell organelles that are responsible for the recycling of internal cellular material, repair of the plasma membrane, cell signaling, and partially, energy metabolism.

Structure-function connection

More recently the connection between structure (architecture) and function of dictyosome ribbons in animal cells has been better studied.

The results have allowed us to discover that the Golgi structure per se constitutes a sensor of the stability of the cell and its functioning. That is, in animals, the Golgi macrostructure functions as a witness and reporter of the integrity and normality of cellular functioning.

References

1. Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K. Walters, P. (2014) Molecular Biology of the Cell, 6 ^th Edition. Garland Science, Taylor & Francis Group. Abingdon on Thames, United Kingdom.
2. Gosavi, P., Gleeson, PA (2017) The Function of the Golgi Ribbon Structure - An Enduring Mystery Unfolds! Bioessays, 39. doi: 10.1002 / bies.201700063.
3. Makhoul, C., Gosavi, P., Gleeson, PA (2018) The Golgi architecture and cell sensing. Biochemical Society Transactions, 46: 1063-1072.
4. Pavelk, M., Mironov, AA (2008) The Golgi apparatus: State of the art 110 years after Camillo Golgi's discovery. Springer. Berlin.
5. Tachikawaa, M., Mochizukia, A. (2017) Golgi apparatus self-organizes into the characteristic shape via postmitotic reassembly dynamics. Proceedings of the National Academy of Sciences, USA, 144: 5177-5182.