The definition of cytoplasm
A cell is the structural, functional and biological unit of all organisms. It is a membrane-bound structure containing the protoplasm. The protoplasm is the fluid living content of the cell. In certain references, protoplasm is a synonym of the term cytoplasm. In other sources, the protoplasm includes the nucleoplasm. Thus, in stricter sense, the protoplasm is basically made up of the cytoplasm and the nucleoplasm. The cytoplasm, in turn, is the protoplasmic contents between the cell membrane and the nuclear envelope.
Features of cytoplasm
The cytoplasm is the jelly-like substance of the cell. It pertains to all the contents of a cell except that in a eukaryotic cell it does not include the nucleus. In a eukaryotic cell, the cytoplasm is made up of the cytosol, the vesicles, the cytoskeleton, the inclusions, and the organelles except for the nucleus. The cytoplasm of a eukaryotic cell is that part of the cell between the cell membrane and the nuclear envelope. In fact, the cytoplasm and the nucleus make up the protoplasm of a eukaryotic cell. In prokaryotic cells that do not have a well-defined nucleus, the cytoplasm is simply everything enclosed by the cell membrane. It therefore contains the cytosol, and all the other cellular components, including the chromosome in the nucleoid region. The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, and metabolism are carried out.
In eukaryotic cells, the cytoplasm contains cellular organelles. These organelles perform special functions. The nucleus, for instance, is the organelle that contains the genetic material and therefore it controls cellular activities such as metabolism, growth, and reproduction by regulating gene expression. Chloroplasts are plastids containing green pigments essential for photosynthesis. Mitochondria are the organelles that synthesize energy for multifarious metabolic processes. The endoplasmic reticulum occurs as an interconnected network of flattened sacs or tubules involved in lipid synthesis, carbohydrate metabolism, drug detoxification, and attachment of receptors on cell membrane proteins. It is also involved in intracellular transport, such as the transport of the products (of rough endoplasmic reticulum) to other cell parts like the Golgi apparatus. Golgi apparatus is comprised of membrane-bound stacks. It is involved in glycosylation, packaging of molecules for secretion, transporting of lipids within the cell, and giving rise to lysosomes. Other cytoplasmic structures found in the cytoplasm are vacuoles and ribosomes. In plants, movement of the cytoplasm around vacuoles is referred to as cytoplasmic streaming. Ribosomes, the site of protein synthesis, are comprised of protein and RNA. Some ribosomes are unbound whereas the others are attached to the endoplasmic reticulum.
The cytosol (the part that which remains when the organelles are removed) is the aqueous portion of the cytoplasm in an intact cell. It consists of water, organic molecules, and dissolved ions. The highest percentage of cytosol component is water, i.e. about 70%. The typical ions in the mammalian cytosol are potassium, sodium, chloride, bicarbonate, amino acids in proteins, magnesium, and calcium. The cytosol serves as the site where many chemical reactions take place. In prokaryotes, it is where most metabolic reactions take place (others occur in the cell membrane). In eukaryotes, it is where the organelles and other cytoplasmic structures are suspended. Since the cytosol contains dissolved ions, it plays a role in osmoregulation and cell signaling. It is also involved in generating action potentials such as in endocrine, nerve and muscle cells.
Cytoplasmic biochemical reactions
The cytoplasm is the site of many biochemical reactions, which may be classified into two major types: catabolism and anabolism. Catabolism includes biochemical reactions that break down complex molecules into smaller units. Often, it entails energy release. Anabolism includes biochemical reactions that are ATP-driven. Anabolic processes are biomolecular syntheses, building molecules from smaller units to more complex structures.
Biological functions of cytoplasm
The cytoplasm is a site of growth and metabolism. Various biomolecules are made and degraded in the cytoplasm. For instance, glycolysis occurs in the cytosol. Glycolysis is the initial metabolic pathway of cellular respiration, converting monosaccharide, often glucose, into pyruvate and concomitantly produce high-energy biomolecule, particularly ATP. The remaining processes of cellular respiration (i.e. citric acid cycle and oxidative phosphorylation take place inside the mitochondria.
- Greek kyto-, kýtos (“container”, “receptacle”, “body”) + Greek plásma
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