The Cell: Functions, Characteristics And Structure

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The cell: functions, characteristics and structure

Introduction

The cell is the anatomical and functional unit of living beings, being the smallest structure, capable of performing all the vital functional ones that an organism needs to function properly. We find two types of cells, prokaryotes and eukaryotes, the latter are the only ones that have a cell nucleus, this structure being the most prominent, since it allows the cell to store genetic information in the DNA. In order to understand how the transmission of genetic information of any living organism works, in this test we will address the parts that make up the cell nucleus, as well as the complexes of Poreo and the transport of proteins to the interior and exterior of the nucleus.

Developing

The nucleus is a structure formed by a double membrane that is known as nuclear wrapping, it can measure around 5um in diameter, being much greater than in prokaryotic cells. Within the nucleus is the DNA that corresponds to all the genetic information of the cell. The nucleus has an internal medium called nucleoplasma that contains the DNA fibers called chromatin and small corpuscles constituted by RNAs known as nucleolus. (Gonzalez, 2014)

Nuclear envelope

The nuclear envelope originates from the endoplasmic reticulum and is constituted by:

  • External membrane: It has ribosomes and allows communication with the re membrane.
  • Internal membrane: It has transmembrane proteins that are used as anchor for proteins that form the nuclear lamina.
  • Perinuclear Space: It is similar to cytoplasm
  • Nuclear sheet: It has fibrillary proteins which bind to the internal membrane and chromatin fibers. Its function is to serve as an envelope support.
  • Nuclear pores: They are formed by proteins and pierce the structure. Its function is to regulate the passage of cytosol proteins to the nucleus. 

 

Nuclear wrapping functions

  • Separate the cytosol from the nucleoplasma so that the metabolic processes of the two means are not mixed.
  • Regulate substance exchange through pores.
  • Allows the union to be carried out with the DNA fibers to form the chromosomes. (Gonzalez, 2014)

 

Nuclear sheet

The nuclear sheet is formed by a network of intermediate filaments that surround the entire nucleus except for pores. (Gonzalez, 2014)

Functions:

  • Its thickness is 30 to 100nm
  • It is important in the assembly of the nuclear wrapping and in the exit of the cytosolic material inside the nucleus.
  • Formed by intermediary filaments called laminar
  • Allows the formation of the nucleus
  • In birds and mammals it is formed by 3 sheets: A (74kda), B (72kda) and C (62kda)
  • It is a nucleosqueleto that has as a function the distribution of chromosomes during the interface.

Nuclear matrix

It constitutes the structural skeleton of the nucleus, is formed by actin microfilaments and is important since it maintains cell morphology and allows the directional movement of products and substances such as: ribosomal subunits, RNAm, among others. It should also be noted that it meets a main role that is to serve as a RNA guide to be transported from the place of transcription to pore complexes. (Rebolledo, 2015)

Nucleolus

It is a spherical structure that does not have a membrane and is formed by RNA and proteins. The nucleolus is organized through the so -called nuclear organizers, which are sites located in the different chromosomes. Nucleoli are able to increase their number and size when the cell is stimulated or participates in protein synthesis. An important fact is that the nucleoli disappear in cell division and form again in the chromosome nucleolar centers. Its main function is to manufacture ribosomal RNA, necessary for the synthesis and formation of ribosomas. (Gonzalez, 2014)

Chromatin

It is the main substance of the cell nucleus, it is formed by DNA filaments which are found in different degrees of condensation. Chromatin is found in the peripheral regions of the interface. (Gallegos, 2014) For chromatin to fulfill its respective functions, it must be extended, since otherwise it is not active. In cell division, this substance condenses to form chromosomes.Once the cell division is over, chromatin is depolarized and two types of chromatin are distinguished. Heterochromatin: corresponds to the condensed form of chromatin and can be:

  1. Constitutive Heterochromatin: which is condensed in all cells in an organism
  2. Optional heterochromatin: which is condensed in just some body cells.

Euchromatin: corresponds to the diffuse form of chromatin, which is more abundant in active cells than in which they are transcribing. (Gonzalez, 2014) Chromatin is responsible for facilitating genetic information with the purpose of cell organelles performing the synthesis and protein transcription. In addition it also allows to conserve and transmit the genetic information of DNA, to later double it during cell reproduction. (Gallegos, 2014)

Chromosomes

They are structures that have a baston shape and appear during the division of the nucleus, they are constituted by histones and DNA. Each chromosome is formed by two strands of DNA or also called chromatids together by a centromere, which is surrounded by a protein structure, known as Cinetocoro, which fulfills the function of organizing microtubules to facilitate the separation of both chromatids. The fundamental role played by chromosomes is to allow the transmission of the genetic information of the stem cell to daughter cells. (Gallegos, 2014)

Nuclear pores

They are large molecular aggregates that are located in the openings of the outer and internal membrane and allow the communication of the cytoplasm and the nucleoplasma. They are very numerous, approximately 3000 to 4000 pores per nucleus. The nuclear pores are formed by proteins called nucleoporins and vary according to the species, for example, mammals have about 400 nucleoporins while yeasts have only 30 nucleoporins and metazoos have about 40. (Guamán, 2017)

Pore complexes

It is a complex structure that has a diameter of 120nm with a weight of 125 million daltons and represents the channel by which polar molecules, macromolecules, ions, etc. (Rebolledo, 2015) There are also small clefts between the complexes of 8 units that would represent the means by which they cross and mobilize non -ionic molecules. (Rebolledo, 2015)

The function of the pore complex is to allow the exchange of material and substances between the cytosol and the nucleus. The nucleus and ribosomes are exported from the nucleus and histones, polymerases, lipids, etc. It should be noted that transport through this structure is fast and can be transported simultaneously and in both directions.(Contreras, 2013)

Interior and exterior transport of the nucleus

The transport of molecules inward and outside the nucleus, can be performed thanks to the nuclear envelope since the nuclear pores mediated by the multiproteic complexes are found. There are many transport routes such as import and export proteins (Chaco, 2007)

Protein import

Within the molecules that could be imported to the nucleus were: the DNA polymerases necessary for replication and transcription, proteins for the synthesis of ribosomes and some ions, etc. (Chaco, 2007)

  1. We are going to import a protein to the nucleus, to be recognized by Pore, it has to have a signal molecule to which a nuclear location sequence (SLN) is dominated. A protein called importin is added, which will facilitate the import of protein, nucleoporins cooperation, allow the Pore Diameter to delay. (Balcazar, 2012) (In the nucleus we have the RAN-GEF proteins nucleotide exchanger, it is the protein that will convert the RAN GDP that comes from the cytoplasm in RAN GTP) (Bazán, 2008)
  2.  Once inside the nucleus it is necessary that the protein separates from the importation for this is necessary another protein that is called RAN GTP (Balkzar, 2012)
  3. When Ran GTP one is important to the separation of the protein with the importation, that is, on the one hand, the protein will be free and on the other hand an importing complex RAN GTP
  4.  Once the protein is free;The importine must go back to the cytoplasm since it only works outside the nucleus. (Balkzar, 2012)
  5. The RAN GTP helps in this process all the molecules that leave the nucleus since they must be linked to GTP this complex will come out through the nuclear pores to the cytoplasm. (Balkzar, 2012)
  6.  In the cytoplasm we have another enzyme related to the cycle of the RAN GTP that is the ran-gat enzyme which helps to hydrolyz its GTP to turn it into RAN-GDP, it no longer has an affinity for importaIt is free to return to another molecule that will be transported to the nucleus and the GDP is able to enter only the nucleus and the cycle would be repeated (Balkzar, 2012)

 

Protein export

Molecules that have to be transported from the nucleus to the cytoplasm for example of this type of molecules: ArnM arnr arnr

  1. When exporting a nucleus protein, it must be recognized by PORO, so you have to have a signal molecule called the NES export sequence to which export is to be joined (Mendez, 2014)
  2.  All the molecule that are exported from the nucleus to the cytoplasm must be linked with RAN-GTP, these three united molecules will be those that go through the nuclear pores to the cytoplasm (Mendez, 2014)
  3.  To separate these molecules we have the RAM-GAB in the cytoplasm, which helps to convert RAN GTP into Ran GDP. (Mendez, 2014)
  4.  By becoming Ran GDP, it loses affinity for export, which is released and this in turn loses affinity for the transported protein, being released in the cytoplasm to perform its function. (Mendez, 2014)
  5. The GDP and export are available to return to the nucleus, the RAN-GDP becomes RAN-GTP thanks to the RAN-GEF exchanger proteins;The export is ready to find another molecule that must be transported.

 

Conclusions

The nuclear envelope is a double membrane structure that forms the nucleus by separating the nucleoplasma from the cytosol. It contains chromatin that are DNA filaments, which is responsible for all genetic information and is also the nucleolo that are small RNA fragments. In the structure of the nucleus there are perforations called nuclear pores, they help the exchange of substances between core to cytosol. When chromatin condenses in cell division, it forms chromosomes, constituted by two strands of DNA united by a centromere, in this way it allows the transmission of the genetic information of the stem cell to the daughter cells and when the cell division concludes this isdepolarize and distinguish 2 types of chromatin: heterochromatin and euchromatin.

Bibliography

  1. Balkzar, m. (July 14, 2012). Obtained from https: // is.Slideshare.net/riccibw/ranciclo2
  2. Bazán, l. A. (2008). BIOLOGICAL SCIENCES FACULTY . Obtained from https: file: /// d:/users/user/downloads/thesis%20lidia%20ara%c3%low%20baz%c3%a1n2008.PDF
  3. Chaco, s. P. (7 Wednesday of May 2007). Obtained from http: // www.biology.Edu.AR/CEL_EUCA/FILESPDF/CELLA2.PDF
  4. Contreras, r. (11 of 04 of 2013). Biology. Obtained from nuclear pore: https: // biology.Laguia2000.com/Citologia/El-Poro-Nuclear
  5. Gallegos, g. (16 of 05 of 2014). biology department. Obtained from cell nucleus: https: // institutonational.CL/WP-CONTENT/UPLOADS/2016/06/2-BIOLOGY%C3%ADA-GU%C3%ADA-DE-EL-N%C3%Bacleulular-Cailular.PDF
  6. Gonzalez, J. R. (11 of 08 of 2014). Biology Area Hypertexts. Obtained from cell nucleus: http: // www.biology.Edu.AR/CEL_EUCA/FILESPDF/CELLA2.PDF
  7. Guamán, p. (03 of 2017). Plant and animal histology atlas. Obtained from nuclear pores: https: // mmegias.websites.Uvigo.es/5-ciles/4-by.PHP
  8. Mendez, j. (August 9, 2014). Obtained from https: // www.academy.EDU/24064915/review_tem%c3%a1tico_del_3er._Parcial_de_biolog%c3%ada_celular_cor._Almaceamient
  9. Paz, j. (23 of 12 of 2016). Cell biology. Obtained from cell nucleus: https: // www.Hiru.EUS/Es/Biologia/El-Nucleo-Celular
  10. Rebolledo, i. (07 of 02 of 2015). Interface nucleus. Obtained from http: // bibmed.UCLA.Edu.VE/EDOCS_BMUCLA/MATERIALDIDACTIC/CELLOUS/NUCLEOINTER.PDF

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