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| {{Image|Muncprotein.jpg|right|300px|Inman M ( ) Shape of a common protein module suggests role as molecular switch.}} | | {{:{{FeaturedArticleTitle}}}} |
| '''[[Macromolecular chemistry]]''' is the study of the physical, biological and chemical structure, properties, composition, and reaction mechanisms of [[macromolecules]]. A macromolecule is a molecule that consists of one or more types of repeated 'building blocks'. The building blocks are called [[Monomer|monomeric unit]]s (monomers).
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| Macromolecules (also known as polymer molecules) appear in daily life in the form of [[plastic]], [[styrofoam]], [[nylon]], etc. These [[polymer]]s, i.e., substances consisting of polymer molecules, are of great technological importance and are used in the manufacturing of all sorts of goods, from automobile parts to household appliances. The artificial polymer molecules usually exist of long repetitions of identical monomers, either in chains or networks.
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| In molecular biology macromolecules (biopolymers) play a very important role: the well-known molecules [[DNA]], [[RNA]], and [[polypeptides]] ([[proteins]]) are examples of macromolecules. In molecular biology one is mostly interested in macromolecules in solution, usually dissolved in water. The biological function of macromolecules in living cells is a highly relevant and widely studied topic of research. Although, strictly speaking, biopolymers belong to the class of polymer molecules, there is a tendency not to use the latter name in biological applications, but to speak of macromolecules. The term "polymer" is usually reserved for the substances manufactured in bulk by the chemical industry.
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| In industry, the value of synthetic macromolecules as plastics and nylon, has risen enormously over the last 60 years. They have made it possible to mould shapes that would have been impossible to create without them. When they were first developed, their resistance to rupture and degradation was seen as a profound advantage, but nowadays we seek more biologically degradable plastics such as polyethyleneglycol that pollute the environment less.
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| Biological macromolecules include, besides the molecules already mentioned, [[enzyme]]s, and [[polysaccharide]]s, such as cellulose and starch. The better understanding of the basic behavior of polymer molecules has enhanced our knowledge of these biological molecules, and studies of partially charged [[polyelectrolytes]] have led to a deeper insight into their biological function. The investigations of the three-dimensional structure of macromolecules, (their [[configuration]] and [[conformation]]), have led to the identification of specific regions that perform specialized activities. A good example is the catalytic role of particular amino acid residues in polypeptide enzymes and the role of [[functional group]]s such as [[biotin]] or [[riboflavin]] in cellular metabolism. The folding of macromolecules is now a topic of much scientific investigation, since the correct folding of these polymers is a critical factor for normal function. Abnormal folding of particular proteins is the cause of several diseases, including [[Alzheimer disease|Alzheimer's]] and [[Creutzfeldt-Jakob disease]] (CJD) .
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Latest revision as of 10:19, 11 September 2020
1901 photograph of a stentor (announcer) at the Budapest
Telefon Hirmondó.
Telephone newspaper is a general term for the telephone-based news and entertainment services which were introduced beginning in the 1890s, and primarily located in large European cities. These systems were the first example of electronic broadcasting, and offered a wide variety of programming, however, only a relative few were ever established. Although these systems predated the invention of radio, they were supplanted by radio broadcasting stations beginning in the 1920s, primarily because radio signals were able to cover much wider areas with higher quality audio.
History
After the electric telephone was introduced in the mid-1870s, it was mainly used for personal communication. But the idea of distributing entertainment and news appeared soon thereafter, and many early demonstrations included the transmission of musical concerts. In one particularly advanced example, Clément Ader, at the 1881 Paris Electrical Exhibition, prepared a listening room where participants could hear, in stereo, performances from the Paris Grand Opera. Also, in 1888, Edward Bellamy's influential novel Looking Backward: 2000-1887 foresaw the establishment of entertainment transmitted by telephone lines to individual homes.
The scattered demonstrations were eventually followed by the establishment of more organized services, which were generally called Telephone Newspapers, although all of these systems also included entertainment programming. However, the technical capabilities of the time meant that there were limited means for amplifying and transmitting telephone signals over long distances, so listeners had to wear headphones to receive the programs, and service areas were generally limited to a single city. While some of the systems, including the Telefon Hirmondó, built their own one-way transmission lines, others, including the Electrophone, used standard commercial telephone lines, which allowed subscribers to talk to operators in order to select programming. The Telephone Newspapers drew upon a mixture of outside sources for their programs, including local live theaters and church services, whose programs were picked up by special telephone lines, and then retransmitted to the subscribers. Other programs were transmitted directly from the system's own studios. In later years, retransmitted radio programs were added.
During this era telephones were expensive luxury items, so the subscribers tended to be the wealthy elite of society. Financing was normally done by charging fees, including monthly subscriptions for home users, and, in locations such as hotel lobbies, through the use of coin-operated receivers, which provided short periods of listening for a set payment. Some systems also accepted paid advertising.
