The basic structure that a cell fills within the outer cell membrane (plasmalemma) is called cytoplasm or cytoplasm (from ancient Greek κύτος kýtos , German 'vessel' , 'cavity' and πλάσμα plásma , German 'structure' ) .
The cytoplasm consists of the cytosol as the liquid phase together with the substances and proteins dissolved in it and the solid cytoskeleton . In the cytoplasm there are also various organelles that can be separated by membranes and are occasionally included. In the case of eukaryotic cells ( eucytes ), the nucleus surrounded by the cytoplasm is usually considered separately and its contents, which are enclosed by the nuclear membrane, are referred to as the caryoplasm .
The word "cytoplasm" was introduced by the German anatomy professor Albert von Kölliker in 1863 as a synonym for " protoplasm ". It was not until 1882 that the cell plasma without nucleus and plastids was called cytoplasm at the suggestion of Eduard Strasburger .
The cytoplasm is the basic substance of the cell. The entire basic substance together with the cell organelles is called protoplasm. If the cell organelles are removed by centrifugation, the product is called a cytosol. While the cytoplasm is more viscous at the cell edges and is known as the ectoplasm , it is more fluid inside and is called the endoplasm . Undifferentiated plasma deposits are also called paraplasm .
Prokaryotes and endosymbionts
When cytoplasm is mentioned, a eukaryotic cell (eucyte) is often assumed - as is the case here. The term stroma is more common for the cytoplasm of prokaryotic cells ( procytes , also protocytes), especially in bacteria .
According to the endosymbiont theory , a number of organelles in the eucytes are derived from bacteria, the plastids ( chloroplasts , leucoplasts , rhodoplasts, etc.) on the one hand and the mitochondria , hydrogenosomes and mitosomes on the other. The interior (plasma) of these organelles, often called the matrix , is therefore derived from the stroma of the bacterial ancestors, it is homologous to this . These organelles usually have their own DNA , unless it has been completely transferred to the cell nucleus by endosymbiotic gene transfer. As with bacteria, this is condensed within the stroma in a nuclear sphere (nuclear equivalent, nucleoid ).
Many different chemical metabolic processes of the cell take place within the cytoplasm , which are controlled by enzymes . Here energy must be provided for all processes in all cells. In addition, there are cell-specific tasks such as the formation of additional cell components during growth , the breakdown of undesired substances and the build-up of substances to be stored or released, and the transport of molecules through the membranes and through the cell.
Biomembranes serve in the cytoplasm to enclose additional differently shaped spaces and to delimit them from one another. Such membrane-bounded spaces within the cytoplasm are called compartments or cell organelles , as they, as it were, as "organs of the cell" fulfill certain functions in cell metabolism . Due to the different reaction spaces created in this way, opposing metabolic processes such as carbohydrate breakdown and carbohydrate build-up or oxidation and reduction processes can take place simultaneously within the cytoplasm .
The consistency of the cytoplasm can alternate between gel and sol , allowing movement of all particles trapped in the cytoplasm. This consistency results from the fact that most of the water is bound in hydration shells .
Chemical composition of the cytoplasm
From a chemical point of view, the cytoplasm consists of numerous organic , but also inorganic substances. With 80 to 85 percent water, the water content is high. The following list shows the average composition of animal cells:
- Water 80.5–85%
- Proteins 10-15%
- Lipids 2-4%
- Polysaccharides 0.1-1.5%
- DNA 0.4%
- RNA 0.7%
- small organic molecules 0.4%
- inorganic molecules and ions 1.5%
The pH of the cytoplasm is usually around seven. However, since protons are often bound or released during metabolic reactions , the cytoplasm is buffered . The pH value can also be changed or stabilized using ion pumps.
The cytoskeleton , which is dynamically built up and broken down, is located in the cytoplasm . This stabilizes the cell, provides solid pathways for vesicle transport and causes intracellular movements such as cytoplasmic flow, organelle and chromosome transport. The cytoplasmic flow only takes place in the endoplasm, it contributes to the mixing.
- Werner Buselmaier: Biology for Physicians . 10th edition. Springer, Heidelberg 2007, ISBN 978-3-540-29374-3 .
- Neil A. Campbell: Biology . Spectrum, Heidelberg 1998, ISBN 3-8274-0032-5 .
- Wilhelm Gemoll : Greek-German school and hand dictionary. Munich 1965.
- Helga Güttler: The terms plasma and protoplasm: their development and change in biology. In: Rete. 1, No. 3/4, 1972, pp. 365-375, especially p. 374.
- Ralf-Rainer Mendel: Cell biology of plants . Ulmer, Stuttgart 2010, ISBN 978-3-8252-3423-2 , pp. 33 .