Microstructures of the Cell
The cytoplasm can be divided into four structural units: hyaloplasm, cell organelles, metaplasm, and paraplasm.
Hyaloplasm forms the main substance of the cell body. It is made up of the jelly-like cytoplasm, a protein colloid in which filamentous protein molecules join together to form a spatial lattice, a matrix of protein filaments on which to suspend the cell organelles and other working structures. The hyaloplasm comprises 70% to 80% water, approximately 10% proteins, around 2% nucleic acid (RNA and DNA), and about 1% lipoids (fatlike substances) and fats, as well as organic materials such as sugar and inorganic ions (eg, sodium chloride and calcium). In addition to this matrix, ribosomes and the endoplasmic reticulum are present.
The endoplasmic reticulum is a branched system of fissures and cavities; it is a working structure of protein synthesis in which constructive metabolism takes place. Proteins, carbohydrates, and lipids are synthesized here and broken down to produce cell components. Broken-down carbohydrates are stored in oval structures called cyto-somes. Ribosomes are found on the membrane of the (rough) endoplasmic reticulum.
The ribosomes form the working structure of protein synthesis, which means they form the templates for special protein molecules: the RNA molecules. The matrices for identical replication of RNA molecules are found on the surface of the ribosomes.
Ribosomes and endoplasmic reticulum, to put it simply, can be seen as duplicating material for the RNA molecules, while the RNA molecules represent the duplicating material by which the DNA molecules are produced. DNA molecules are the finished protein molecules, in which all the "blueprints and working instructions" for the structure and function of a cell are stored.
Cell organelles are the small organs of a cell and include:
- The mitochondria, threadlike or oval structures comprising a lamellar system with an outer and inner membrane.They contain active substances (enzymes) for organic oxidation. The respiratory enzymes of the mitochondria can break down amino acids, fats, and glucose with the aid of oxygen while generating heat; therefore, these organelles can be seen as the cell's energy suppliers.
- The Golgi apparatus, a vesicular membrane system in which the secretory activities of the cell take place.This is where the cell's secretions are stored, altered, and if required, released as a functioning secretion. The Golgi apparatus is mainly found in glandular cells.
- The centrosome (centrosphere, centriole), which only becomes active upon cell division, when it produces protein threads, with which it arranges, divides, and attracts the chromosome threads to itself.
- Lysosomes, which contain enzymes to break down molecules that are then further broken down by the special enzymes of the mitochondria.
Metaplasm is made up of specific fibrous structures with functional tasks:
- Tonofibrils: give the cell special resistance to tensile stress
- Myofibrils: can contract like muscle cells
- Neurofibrils: conduct nerve impulses
Paraplasm is made up of dead cell inclusions, which have either been absorbed from outside or developed as degradation products from the breakdown of nutrients. However, so-called reserve carbohydrates can also be found as paraplasm, and these are still of use for cell metabolism.