What is perfusion culture

Cell (biology)

A cell (Latin cellula, small chamber, cell) is the smallest living unit of all organisms. One distinguishes Unicellular organisms, that is, living beings that only consist of one cell, and Multi-cell, that is, living beings that consist of more than just one cell. Does the living being consist of many cells (Multi-cell), cells can be connected to functional units and thereby form tissue. The human body consists of several hundred different types of cells and tissues. From an evolutionary point of view and compared to unicellular organisms, the cells of multicellular organisms have largely lost their ability to live on their own and have specialized in a division of labor in tissues.

The science and doctrine of the cells of living beings is cytology (ancient Greek κύτοςkytos, German 'cell').

Basics

Each cell is a structurally definable, independent and self-sustaining system. It is able to absorb nutrients and to use the energy bound in them through metabolism. New cells are created through cell division. The cell contains the information for all of these functions or activities. Cells have basic abilities called the characteristics of life, although not every cell is required to have all of these characteristics:

In the course of evolution, two groups of living beings have formed which differ greatly in the structure of their cells: on the one hand, the prokaryotes, which consist of simply built cells without a nucleus, and on the other hand, the eukaryotes, which consist of cells that are much more complicated are structured and have a nucleus. Prokaryotes and eukaryotes can occur both as unicellular and multicellular cells. In multicellular cells, cells form what are known as special purpose associations. Most of the time they share functions and are often no longer viable individually. The abilities described above are limited by specializing in multicellular animals.

The size of cells varies greatly. Usually they are between 1 and 30 microns in diameter; Egg cells from higher animals are often significantly larger than the other cells. For example, the egg cell of an ostrich has a diameter of over 70 mm. The human egg cell has a diameter of 0.15 mm; it is its largest cell and the only one that can be seen with the naked eye.

The prokaryotic cell

Scheme of a prokaryotic cell (bacterium)

Prokaryotic cells do not have a real nucleus like eukaryotic cells and have a simpler internal organization than eukaryotic cells. They are also known as Procytes or Protocytes. Living beings with prokaryotic cells are called Prokaryotes. They include the bacteria and the archaea. They usually appear as single-celled organisms.

Prokaryotic cells and eukaryotic cells can generally be distinguished from one another by the following features:

  • They have a simpler structure than eukaryotic cells, they rarely form compartments.
  • The DNA is free in the cytoplasm and is not stabilized by histones (special proteins), so it is not organized in a real chromosome. It is arranged in a small space and is called a nucleoid.
  • The genome usually only consists of a single DNA molecule, which is referred to as a "bacterial chromosome". Often this DNA molecule is self-contained.
  • The cell envelopes often have a complex structure, sometimes even with two membranes.
  • The ribosomes are always smaller (sedimentation coefficient 70 S) than in eukaryotic cells (80 S).

Prokaryotes are characterized by a wide range of physiological and ecological types. Some are viable even under extreme conditions (temperature range up to over 100 ° C); oxic or anoxic environment; acidic environment (pH 1-4); high hydrostatic pressures (1000 bar). Many live parasitically, symbiotic or saprovor, some are pathogenic (disease-causing). They often contain plasmids (extrachromosomal, self-contained or linear elements of DNA). Furthermore, prokaryotes have only a limited ability to differentiate, for example in spore formation (including endospore formation in Bacillus subtilis).

The eukaryotic cell

Eukaryotic cells are also called Eucytes designated. The main difference to prokaryotic cells (procytes) is the existence of a cell nucleus with a nuclear envelope around the DNA organized in chromosomes. The nuclear envelope consists of two membrane layers with a space in between, a so-called double membrane, and is typically around 15 nanometers thick. Eukaryotic cells are much more differentiated than prokaryotic cells. Their multitude results from the very different functions that they have to fulfill. - The mean cell mass of eucytes is around 2.5 nanograms. Their length ranges from a few micrometers to several centimeters in the case of myocytes (muscle fiber cells).

Nerve cells (neurons) occupy a special position among the eucytes. These extend from the spinal cord into the peripheral extremities.

Differences between plant, animal and fungal cells

Cells from animals, plants, and fungi are eukaryotic cells, but there are some differences in their structure. Characteristic differences are listed in a table below.

propertyplant cellsanimal cellsFungus cells
Cell wall, main components always present, with cellulose, in softwood also a lot of glucomannan, often as galactoglucomannanalways without cell wallsregularly available[1], with chitin (cell walls can, however, be omitted between cells)
Plastidsalways present, mostly as (green) chloroplastsnever existednever existed[2]
Vacuolesalways present (surrounding membrane: tonoplast)mostly absent (but characteristic of adipocytes)always present[1]
high-energy carbohydrate storage molecule StrengthGlycogen[3]Glycogen[3]
Intercellular space in tissuesMiddle lamella with contact areas (pits), no collagenExtracellular matrix, always with collagenno collagen
Cell division (usually cell membrane constriction, budding can also occur) then formation of the cell wall between the daughter cells
Exchange of substances with neighboring cells partly via plasmodesmata, which result from cell divisionvia desmosomes or gap junctions, which have emerged as new formations after complete cell divisionGap junctions or similar structures
Lysosomesmay or may not be includedpresent, often in the role of a lytic vacuole
Cell nucleus in the interphasealways present singularlymostly present (absent e.g. in human erythrocytes)mostly present, may not be found in plasmodia or syncytia or be present several times (merging of several neighboring cells without intervening cell walls and cell membranes)

Peculiarities of plant cells

  • The cell wall is designed in such a way that it gives the cell and thus the entire plant body a more or less solid shape. It is permeable to water, dissolved nutrients and gases. It consists mainly of cellulose. In cells with thick cell walls through which substances are still transported, there are pits in the cell walls. These are openings in the cell wall through which neighboring cells - separated only by a thin membrane - are in contact with one another and through which the exchange of substances is facilitated.
  • The chloroplasts contain a complex system for using light energy for photosynthesis, which among other things contains chlorophyll (a green dye). The energy of light is captured (absorbed), converted into chemical energy in the form of glucose and stored in the form of starch.
  • The vacuoles are spaces in the cytoplasm that are filled with cell sap. This can contain dyes (for example flavones), toxins (for example caffeine), fragrances and others.
  • The tonoplast is the selectively permeable membrane that separates the vacuole from the plasma.

Structure of the cell

Every cell, whether prokaryotic or eukaryotic, has a cell membrane. This cell membrane separates the cell from its environment and controls what is taken in and what is transported out of the cell. There are ions in different concentrations on each side of the cell membrane. The cell membrane maintains this difference in concentration, which creates a chemical potential. The medium enclosed by the cell membrane is the cytoplasm. All cells capable of dividing have DNA, in which the genetic information is stored, as well as proteins which, as enzymes, catalyze reactions in the cell or form structures in the cell, and RNA, which is primarily necessary for the construction of proteins. Important cell components are listed and briefly described below:

Cell membrane - the protective cover

Each cell is enclosed by a cell membrane (also called a plasma membrane or sometimes called a pellicle). This membrane separates the cell from the environment and also protects it. It mainly consists of a double lipid layer and various proteins that, among other things, enable the exchange of ions or molecules between the cell and its environment. Their thickness is around 4 to 5 nm.

Cell cortex

The cytoplasmic layer, which lies directly on the inside of the cell membrane, is referred to as the cell cortex (also cell cortex, syn. Actin cortex or actomyosin cortex). It is a special layer of cytoplamatic proteins rich in cytoskeletal elements.[4][5][6]

Cell skeleton - the framework of the cell

The cell skeleton gives the cell its shape and mechanical stability. The cell skeleton also fulfills other functions. It is responsible for active movements of the cell as a whole, as well as for movements and transport within the cell. It also plays an important role in cell division and the reception of external stimuli and their transmission into the cell.

In eukaryotic cells, the cell skeleton consists mainly of three types of different protein filaments: microfilaments (actin filaments), microtubules and intermediate filaments.

The existence of the three cytoskeletal elements as the basic equipment of every cell was recognized in the 1960s using electron microscopy and novel fixation (glutaraldehyde fixation) and detection methods (actin decoration by myosin head groups) and goes back to the pioneering work of Sabatini and Ishikawa.[7][8]

The genetic material

There are two types of genetic material in the cell: deoxyribonucleic acids (DNA) and ribonucleic acids (RNA). Organisms use DNA to store information over a long period of time. The RNA is often used to transport the information (for example mRNA) and for enzyme-like reactions (for example rRNA).

In prokaryotes, the DNA is in a simple, self-contained (“circular”) form. This structure is called the bacterial chromosome, although it differs considerably from the chromosomes of eukaryotic cells. In eukaryotic cells, the DNA is distributed in different places: in the cell nucleus and in the mitochondria and plastids, cell organelles with a double membrane. In the mitochondria and the plastids, the DNA is "circular" like in prokaryotes. The DNA in the cell nucleus is organized linearly in so-called chromosomes. The number of chromosomes varies from species to species. The human cell has 46 chromosomes.

Ribosomes - The Protein Factories

The ribosomes are complexes made up of RNA and proteins in prokaryotes and eukaryotes. They are responsible for the synthesis of proteins from amino acids. The mRNA serves as information for the type and sequence of the amino acids in the proteins. Protein biosynthesis is very important for all cells, which is why there are many ribosomes in the cells, sometimes hundreds to thousands of ribosomes per cell. Their diameter is 18 to 20 nm.

Centrioles

Centrioles are cylindrical structures measuring around 170 × 500 nanometers. They are involved in the formation of the MTOC (microtubule organizing center), which forms the spindle apparatus for separating the chromosomes during mitosis, but also contributes to the organization and physical stabilization of the cell during the interphase. Centrioles occur in most animal cells and the cells of lower plants, but not in higher plants (angiosperms).

The organelles

In multicellular organisms, the cells are usually grouped into tissues that specialize in certain functions. Such tissues often form a complex called an organ. In humans, for example, the lungs are responsible for the gas exchange of carbon dioxide and oxygen. There are similar function-related structures on the smallest scale within the cell. Such organelles can be found in every eukaryotic cell. The structure of plant and animal cells partly differs in the number and function of some organelles. Important organelles are listed below.

Cell nucleus - the control center of the cell

The cell nucleus forms the control center of the eukaryotic cell: it contains the chromosomal DNA and thus the majority of the genes. In mammalian cells it has a diameter of 6 µm. The nucleus is separated from the cytoplasm by the nuclear envelope, a double membrane with a gap, total thickness about 35 nm. It is broken through by nuclear pores, which enables an exchange of molecules between the substance of the nucleus interior, the so-called karyoplasm, and the cytoplasm. The outer membrane of the nuclear envelope is connected to the endoplasmic reticulum. The synthesis of RNA (transcription) takes place in the cell nucleus. Those RNA types that are required for protein synthesis (translation) are transported from the cell nucleus through the nuclear pores into the cytoplasm. With a light microscope, a globular structure with a diameter of about 2 to 5 µm can be seen in the nucleus, which is called a nucleus or nucleolus. The DNA in this area of ​​the nucleus contains the blueprints for the ribosomal RNA, i.e. for the catalytic RNA of the ribosomes.

Mitochondria - the power plants

The mitochondria belong to the self-reproducing organelles and are only contained in eukaryotic cells, and in varying numbers. They contain their own genome, which contains many, but not all, of the genes that are important for the mitochondria. The other genes are in the chromosomes in the nucleus. Therefore the mitochondria are semi-autonomous. Mitochondria are called the “energy power plants” of the cell. In them the oxidation of organic substances with molecular oxygen takes place, whereby energy is released and stored in the form of chemical energy (as ATP). They have a diameter of about 0.5 to 1.5 µm and are about 0.8 to 4 µm long.

Plastids

Plastids only exist in eukaryotes that carry out photosynthesis, i.e. plants and algae. Like the mitochondria, the plastids have their own genome and, like the mitochondria, are self-reproducing, i.e. also semi-autonomous. There are different plastids, all of which are derived from the so-called "proplastid". They are able to transform into a different plastid shape. The chloroplast is the most frequently mentioned. It is used to use light to build up organic substances (photosynthesis) and contains all cell components required for photosynthesis, especially membrane systems with chlorophyll, auxiliary dyes, electron and hydrogen carriers and ATP synthase as well as enzymes of the Calvin cycle for CO2-Assimilation. Another plastid is, for example, amyloplast, which is able to store starch, an end product of photosynthesis.

Endoplasmic reticulum and Golgi apparatus

These two systems consist of cavities bounded by membranes and are found in most eukaryotes. They are functionally closely linked. The endoplasmic reticulum (ER) is the fast transport system for chemical substances; the new nuclear membrane is also pinched off by the ER during mitosis. It is also important for translation, protein folding, post-translational modifications of proteins and protein transport. These proteins are then "distributed" by the Golgi apparatus. In the Golgi apparatus, the proteins are modified, sorted and transported to their destination. Defective proteins are sorted out and broken down.

Lysosomes and peroxisomes - the digestive organelles of the cell

Lysosomes are tiny cell organelles in eukaryotes that are enclosed by a membrane. They contain hydrolytic enzymes and phosphatases. Their main function is to digest foreign matter absorbed by the enzymes they contain. In plants, cell sap vacuoles perform the tasks of the lysosomes. Peroxisomes (glyoxisomes in the storage tissue of plant seeds), also called microbodies, are evolutionarily very old cell organelles in eukaryotic cells. They act as detoxification machines. The peroxisomes contain around 60 enzymes called monooxygenases and oxidases, which catalyze the oxidative breakdown of fatty acids, alcohol and other harmful compounds.

Vacuole - storage and detoxification organ

Vacuoles are large reaction spaces enclosed by a membrane, mainly in plants, which can occupy up to 90% of the cell volume, but can also occur, for example, in paramecium. They perform a wide variety of tasks, including maintaining cell pressure (turgor), storing toxic substances, coloring the cell, digesting macromolecules and, in the case of the contractile vacuole, excreting water.

The history of the cell's discovery

Please refer:History of Cell Biology

Cells as drugs

Cells and tissues can also be used as advanced therapy drugs to treat diseases.

See also

literature

  • May-Britt Becker, Armin Zülch, Peter Gruss: From the undifferentiated cell to the complex organism: Concepts of ontogeny. In: Biology in our time. Vol. 31, No. 2, 2001, ISSN0045-205X, pp. 88-97.
  • David S. Goodsell: How cells work. Economy and production in the molecular world. 2nd Edition. Spectrum, Akademischer Verlag, Heidelberg 2010, ISBN 978-3-8274-2453-2.
  • Friedrich Marks: Data processing through protein networks: the brain of the cell. In: Biology in our time. Vol. 34, No. 3, 2004, pp. 159-168.
  • Sabine Schmitz: The experimenter. Cell culture. Elsevier, Spektrum, Akademischer Verlag, Munich 2007, ISBN 978-3-8274-1564-6.
  • Sven P. Thoms: Origin of life (= Fisherman 16128 Fischer compact). Fischer, Frankfurt am Main 2005, ISBN 3-596-16128-2.
  • Joachim Ude, Michael Koch: The cell. Atlas of the ultrastructure. 3. Edition. Spektrum, Akademischer Verlag, Heidelberg and others 2002, ISBN 3-8274-1173-4.
  • Klaus Werner Wolf, Konrad Joachim Böhm: Organization of microtubules in the cell. In: Biology in our time. Vol. 27, No. 2, 1997, pp. 87-95.
  • Gerald Karp: Molecular cell biology. 1st German edition. Springer, Berlin / Heidelberg and others 2005 (table of contents under http://www.gbv.de/dms/hebis-mainz/toc/128186429.pdf).

Web links

- Collection of pictures, videos and audio files

Individual evidence

  1. abC. J. Alexopoulos, C. W. Mims, M. Blackwell: Introductory Mycology. John Wiley and Sons, 1996, ISBN 0-471-52229-5.
  2. Plastids - Lexicon of Biology. Retrieved November 19, 2016.
  3. abJ. Lomako, W. M. Lomako, W. J. Whelan: Glycogenin: the primer for mammalian and yeast glycogen synthesis. In: Biochim. Biophys. Acta., Volume 1673, 2004, pp. 45-55 (PMID 15238248).
  4. ↑ Bruce Alberts, Dennis Bray, Karen Hopkin, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Peter Walter; Jochen Graw (Ed.): Textbook of molecular cell biology. Wiley-VCH, 4th edition 2012, ISBN 978-3-527-32824-6; P. 405.
  5. ^ Cell cortex, on: Spectrum Lexicon of Biology.
  6. ^ Cell cortex, on: DocCheck Flexikon.
  7. ↑ Sabatini et al., 1963 J. Cell Biol.
  8. ↑ Ishikawa et al., 1968 J. Cell Biol.