Math Is Fun Forum

2450) Tunnel

Gist

A tunnel is a passage that runs underground or through something, like a train tunnel that cuts through a mountain. Some theme parks have networks of underground tunnels so that employees can move around out of sight of visitors.

Some tunnels, like New York's Lincoln Tunnel and the Holland Tunnel, which connect New York City to New Jersey, are large and solid enough to drive cars through. Others are much smaller, like the tunnels small animals dig through snow or soil for safety and shelter.

Summary

A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is usually completely enclosed except for the two portals common at each end, though there may be access and ventilation openings at various points along the length. A pipeline differs significantly from a tunnel, though some recent tunnels have used immersed tube construction techniques rather than traditional tunnel boring methods.

A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. The central portions of a rapid transit network are usually in the tunnel. Some tunnels are used as sewers or aqueducts to supply water for consumption or for hydroelectric stations. Utility tunnels are used for routing steam, chilled water, electrical power or telecommunication cables, as well as connecting buildings for convenient passage of people and equipment.

Secret tunnels are built for military purposes, or by civilians for smuggling of weapons, contraband, or people. Special tunnels, such as wildlife crossings, are built to allow wildlife to cross human-made barriers safely. Tunnels can be connected together in tunnel networks.

A tunnel is relatively long and narrow; the length is often much greater than twice the diameter, although similar shorter excavations can be constructed, such as cross passages between tunnels. The definition of what constitutes a tunnel can vary widely from source to source. For example, in the United Kingdom, a road tunnel is defined as "a subsurface highway structure enclosed for a length of 150 metres (490 ft) or more." In the United States, the NFPA definition of a tunnel is "An underground structure with a design length greater than 23 m (75 ft) and a diameter greater than 1,800 millimetres (5.9 ft)."

Details

Tunnels and underground excavations are horizontal underground passageway produced by excavation or occasionally by nature’s action in dissolving a soluble rock, such as limestone. A vertical opening is usually called a shaft. Tunnels have many uses: for mining ores, for transportation—including road vehicles, trains, subways, and canals—and for conducting water and sewage. Underground chambers, often associated with a complex of connecting tunnels and shafts, increasingly are being used for such things as underground hydroelectric-power plants, ore-processing plants, pumping stations, vehicle parking, storage of oil and water, water-treatment plants, warehouses, and light manufacturing; also command centres and other special military needs.

True tunnels and chambers are excavated from the inside—with the overlying material left in place—and then lined as necessary to support the adjacent ground. A hillside tunnel entrance is called a portal; tunnels may also be started from the bottom of a vertical shaft or from the end of a horizontal tunnel driven principally for construction access and called an adit. So-called cut-and-cover tunnels (more correctly called conduits) are built by excavating from the surface, constructing the structure, and then covering with backfill. Tunnels underwater are now commonly built by the use of an immersed tube: long, prefabricated tube sections are floated to the site, sunk in a prepared trench, and covered with backfill. For all underground work, difficulties increase with the size of the opening and are greatly dependent upon weaknesses of the natural ground and the extent of the water inflow.

History:

Ancient tunnels

It is probable that the first tunneling was done by prehistoric people seeking to enlarge their caves. All major ancient civilizations developed tunneling methods. In Babylonia, tunnels were used extensively for irrigation; and a brick-lined pedestrian passage some 3,000 feet (900 metres) long was built about 2180 to 2160 bce under the Euphrates River to connect the royal palace with the temple. Construction was accomplished by diverting the river during the dry season. The Egyptians developed techniques for cutting soft rocks with copper saws and hollow reed drills, both surrounded by an abrasive, a technique probably used first for quarrying stone blocks and later in excavating temple rooms inside rock cliffs. Abu Simbel Temple on the Nile, for instance, was built in sandstone about 1250 bce for Ramses II (in the 1960s it was cut apart and moved to higher ground for preservation before flooding from the Aswān High Dam). Even more elaborate temples were later excavated within solid rock in Ethiopia and India.

The Greeks and Romans both made extensive use of tunnels: to reclaim marshes by drainage and for water aqueducts, such as the 6th-century-bce Greek water tunnel on the isle of Samos driven some 3,400 feet through limestone with a cross section about 6 feet square. Perhaps the largest tunnel in ancient times was a 4,800-foot-long, 25-foot-wide, 30-foot-high road tunnel (the Pausilippo) between Naples and Pozzuoli, executed in 36 bce. By that time surveying methods (commonly by string line and plumb bobs) had been introduced, and tunnels were advanced from a succession of closely spaced shafts to provide ventilation. To save the need for a lining, most ancient tunnels were located in reasonably strong rock, which was broken off (spalled) by so-called fire quenching, a method involving heating the rock with fire and suddenly cooling it by dousing with water. Ventilation methods were primitive, often limited to waving a canvas at the mouth of the shaft, and most tunnels claimed the lives of hundreds or even thousands of the slaves used as workers. In ad 41 the Romans used some 30,000 men for 10 years to push a 3.5-mile (6-kilometre) tunnel to drain Lacus Fucinus. They worked from shafts 120 feet apart and up to 400 feet deep. Far more attention was paid to ventilation and safety measures when workers were freemen, as shown by archaeological diggings at Hallstatt, Austria, where salt-mine tunnels have been worked since 2500 bce.

From the Middle Ages to the present

Canal and railroad tunnels

Because the limited tunneling in the Middle Ages was principally for mining and military engineering, the next major advance was to meet Europe’s growing transportation needs in the 17th century. The first of many major canal tunnels was the Canal du Midi (also known as Languedoc) tunnel in France, built in 1666–81 by Pierre Riquet as part of the first canal linking the Atlantic and the Mediterranean. With a length of 515 feet and a cross section of 22 by 27 feet, it involved what was probably the first major use of explosives in public-works tunneling, gunpowder placed in holes drilled by handheld iron drills. A notable canal tunnel in England was the Bridgewater Canal Tunnel, built in 1761 by James Brindley to carry coal to Manchester from the Worsley mine. Many more canal tunnels were dug in Europe and North America in the 18th and early 19th centuries. Though the canals fell into disuse with the introduction of railroads about 1830, the new form of transport produced a huge increase in tunneling, which continued for nearly 100 years as railroads expanded over the world. Much pioneer railroad tunneling developed in England. A 3.5-mile tunnel (the Woodhead) of the Manchester-Sheffield Railroad (1839–45) was driven from five shafts up to 600 feet deep. In the United States, the first railroad tunnel was a 701-foot construction on the Allegheny Portage Railroad. Built in 1831–33, it was a combination of canal and railroad systems, carrying canal barges over a summit. Though plans for a transport link from Boston to the Hudson River had first called for a canal tunnel to pass under the Berkshire Mountains, by 1855, when the Hoosac Tunnel was started, railroads had already established their worth, and the plans were changed to a double-track railroad bore 24 by 22 feet and 4.5 miles long. Initial estimates contemplated completion in 3 years; 21 were actually required, partly because the rock proved too hard for either hand drilling or a primitive power saw. When the state of Massachusetts finally took over the project, it completed it in 1876 at five times the originally estimated cost. Despite frustrations, the Hoosac Tunnel contributed notable advances in tunneling, including one of the first uses of dynamite, the first use of electric firing of explosives, and the introduction of power drills, initially steam and later air, from which there ultimately developed a compressed-air industry.

Simultaneously, more spectacular railroad tunnels were being started through the Alps. The first of these, the Mont Cenis Tunnel (also known as Fréjus), required 14 years (1857–71) to complete its 8.5-mile length. Its engineer, Germain Sommeiller, introduced many pioneering techniques, including rail-mounted drill carriages, hydraulic ram air compressors, and construction camps for workers complete with dormitories, family housing, schools, hospitals, a recreation building, and repair shops. Sommeiller also designed an air drill that eventually made it possible to move the tunnel ahead at the rate of 15 feet per day and was used in several later European tunnels until replaced by more durable drills developed in the United States by Simon Ingersoll and others on the Hoosac Tunnel. As this long tunnel was driven from two headings separated by 7.5 miles of mountainous terrain, surveying techniques had to be refined. Ventilation became a major problem, which was solved by the use of forced air from water-powered fans and a horizontal diaphragm at mid-height, forming an exhaust duct at top of the tunnel. Mont Cenis was soon followed by other notable Alpine railroad tunnels: the 9-mile St. Gotthard Pass (1872–82), which introduced compressed-air locomotives and suffered major problems with water inflow, weak rock, and bankrupt contractors; the 12-mile Simplon (1898–1906); and the 9-mile Lötschberg (1906–11), on a northern continuation of the Simplon railroad line.

Simplon Tunnel

Nearly 7,000 feet below the mountain crest, Simplon encountered major problems from highly stressed rock flying off the walls in rock bursts; high pressure in weak schists and gypsum, requiring 10-foot-thick masonry lining to resist swelling tendencies in local areas; and from high-temperature water (130° F [54° C]), which was partly treated by spraying from cold springs. Driving Simplon as two parallel tunnels with frequent crosscut connections considerably aided ventilation and drainage.

Lötschberg was the site of a major disaster in 1908. When one heading was passing under the Kander River valley, a sudden inflow of water, gravel, and broken rock filled the tunnel for a length of 4,300 feet, burying the entire crew of 25 men. Though a geologic panel had predicted that the tunnel here would be in solid bedrock far below the bottom of the valley fill, subsequent investigation showed that bedrock lay at a depth of 940 feet, so that at 590 feet the tunnel tapped the Kander River, allowing it and soil of the valley fill to pour into the tunnel, creating a huge depression, or sink, at the surface. After this lesson in the need for improved geologic investigation, the tunnel was rerouted about one mile (1.6 kilometres) upstream, where it successfully crossed the Kander Valley in sound rock.

Most long-distance rock tunnels have encountered problems with water inflows. One of the most notorious was the first Japanese Tanna Tunnel, driven through the Takiji Peak in the 1920s. The engineers and crews had to cope with a long succession of extremely large inflows, the first of which killed 16 men and buried 17 others, who were rescued after seven days of tunneling through the debris. Three years later another major inflow drowned several workers. In the end, Japanese engineers hit on the expedient of digging a parallel drainage tunnel the entire length of the main tunnel. In addition, they resorted to compressed-air tunneling with shield and air lock, a technique almost unheard-of in mountain tunneling.

Subaqueous tunnels

Tunneling under rivers was considered impossible until the protective shield was developed in England by Marc Brunel, a French émigré engineer. The first use of the shield, by Brunel and his son Isambard, was in 1825 on the Wapping-Rotherhithe Tunnel through clay under the Thames River. The tunnel was of horseshoe section 22.25 by 37.5 feet and brick-lined. After several floodings from hitting sand pockets and a seven-year shutdown for refinancing and building a second shield, the Brunels succeeded in completing the world’s first true subaqueous tunnel in 1841, essentially nine years’ work for a 1,200-foot-long tunnel. In 1869 by reducing to a small size (8 feet) and by changing to a circular shield plus a lining of cast-iron segments, Peter W. Barlow and his field engineer, James Henry Greathead, were able to complete a second Thames tunnel in only one year as a pedestrian walkway from Tower Hill. In 1874, Greathead made the subaqueous technique really practical by refinements and mechanization of the Brunel-Barlow shield and by adding compressed air pressure inside the tunnel to hold back the outside water pressure. Compressed air alone was used to hold back the water in 1880 in a first attempt to tunnel under New York’s Hudson River; major difficulties and the loss of 20 lives forced abandonment after only 1,600 feet had been excavated.

The first major application of the shield-plus-compressed-air technique occurred in 1886 on the London subway with an 11-foot bore, where it accomplished the unheard-of record of seven miles of tunneling without a single fatality. So thoroughly did Greathead develop his procedure that it was used successfully for the next 75 years with no significant change. A modern Greathead shield illustrates his original developments: miners working under a hood in individual small pockets that can be quickly closed against inflow; shield propelled forward by jacks; permanent lining segments erected under protection of the shield tail; and the whole tunnel pressurized to resist water inflow.

Once subaqueous tunneling became practical, many railroad and subway crossings were constructed with the Greathead shield, and the technique later proved adaptable for the much larger tunnels required for automobiles. A new problem, noxious gases from internal-combustion engines, was successfully solved by Clifford Holland for the world’s first vehicular tunnel, the Holland Tunnel, completed in 1927 under the Hudson River. Holland and his chief engineer, Ole Singstad, solved the ventilation problem with huge-capacity fans in ventilating buildings at each end, forcing air through a supply duct below the roadway, with an exhaust duct above the ceiling. Such ventilation provisions significantly increased the tunnel size, requiring about a 30-foot diameter for a two-lane vehicular tunnel.

Lincoln Tunnel

Many similar vehicular tunnels were built by shield-and-compressed-air methods—including Lincoln and Queens tunnels in New York City, Sumner and Callahan in Boston, and Mersey in Liverpool. Since 1950, however, most subaqueous tunnelers preferred the immersed-tube method, in which long tube sections are prefabricated, towed to the site, sunk in a previously dredged trench, connected to sections already in place, and then covered with backfill. This basic procedure was first used in its present form on the Detroit River Railroad Tunnel between Detroit and Windsor, Ontario (1906–10). A prime advantage is the avoidance of high costs and the risks of operating a shield under high air pressure, since work inside the sunken tube is at atmospheric pressure (free air).

Seikan Tunnel

Japan’s impressive undersea tunnel, the Seikan Tunnel, is the world’s second longest tunnel (after the Gotthard Base Tunnel in Switzerland) and links the main island of Honshu with the northern neighbouring island of Hokkaido. Much of the tunnel lies under the Tsugaru Strait that separates the two islands. Construction of the tunnel began in 1964 and was completed in 1988. The digging employed as many as 3,000 workers at one time and took 34 lives in all because of cave-ins, flooding, and other mishaps. The tunnel remains one of the most formidable engineering feats of the 20th century.

Machine-mined tunnels

Sporadic attempts to realize the tunnel engineer’s dream of a mechanical rotary excavator culminated in 1954 at Oahe Dam on the Missouri River near Pierre, in South Dakota. With ground conditions being favourable (a readily cuttable clay-shale), success resulted from a team effort: Jerome O. Ackerman as chief engineer, F.K. Mittry as initial contractor, and James S. Robbins as builder of the first machine—the “Mittry Mole.” Later contracts developed three other Oahe-type moles, so that all the various tunnels here were machine-mined—totaling eight miles of 25- to 30-foot diameter. These were the first of the modern moles that since 1960 have been rapidly adopted for many of the world’s tunnels as a means of increasing speeds from the previous range of 25 to 50 feet per day to a range of several hundred feet per day. The Oahe mole was partly inspired by work on a pilot tunnel in chalk started under the English Channel for which an air-powered rotary cutting arm, the Beaumont borer, had been invented. A 1947 coal-mining version followed, and in 1949 a coal saw was used to cut a circumferential slot in chalk for 33-foot-diameter tunnels at Fort Randall Dam in South Dakota. In 1962 a comparable breakthrough for the more difficult excavation of vertical shafts was achieved in the American development of the mechanical raise borer, profiting from earlier trials in Germany.

In 2016 the Gotthard Base Tunnel, the world’s longest and deepest railway tunnel, opened under the Saint-Gotthard Massif in the Lepontine Alps in southern Switzerland. The two tunnels were primarily constructed with four massive tunnel boring machines, Herrenknecht Gripper TBMs; blasting was used for only about 25 percent of the project. An incredible feat of engineering, the tunnel provided a high-speed rail link between northern and southern Europe, forming a mainline rail connection between Rotterdam in the Netherlands and Genoa in Italy.

Hi,

#10675. What does the term in Geography Climax community mean?

#10676. What does the term in Geography Coast mean?

Hi,

#2530. Where are the Bitot's spots situated?

Hi,

#6304.

2397) André Michel Lwoff

Gist:

Work

Bacteriophages are viruses that attach themselves to bacteria, emptying their genetic material into them. At times, many new phage are created quickly, while at other times, new phage are formed only several bacterial generations later. In the early 1950s André Lwoff successfully explained how this process, known as lysogeny, works. The bacteriophage's genes are incorporated into the bacteria's genetic material, but remain latent until a trigger factor causes new phage to be formed. Lwoff also showed that ultraviolet light can be one such factor.

Summary

André Lwoff (born May 8, 1902, Ainay-le-Château, France—died Sept. 30, 1994, Paris) was a French biologist who contributed to the understanding of lysogeny, in which a bacterial virus, or bacteriophage, infects bacteria and is transmitted to subsequent bacterial generations solely through the cell division of its host. Lwoff’s discoveries brought him (with François Jacob and Jacques Monod) the Nobel Prize for Medicine or Physiology in 1965.

Lwoff, born of Russian-Polish parents, was educated at the University of Paris. He spent most of his research career at the Pasteur Institute in Paris, serving on the board of directors from 1966 to 1972. From 1959 to 1968 he was also a professor of microbiology at the Sorbonne in Paris. When he retired from the Pasteur Institute in 1968, he served as director of the Cancer Research Institute at nearby Villejuif until 1972.

In his prizewinning research, Lwoff showed that, after infection, the virus is passed on to succeeding generations of bacteria in a noninfective form called a prophage. He demonstrated that under certain conditions this prophage gives rise to an infective form that causes lysis, or disintegration, of the bacterial cell; the viruses that are released upon the cell’s destruction are capable of infecting other bacterial hosts. Lwoff also discovered that vitamins serve both as growth factors for microbes and as coenzymes. Among his written works are Problems of Morphogenesis in Ciliates (1950) and Biological Order (1962).

After World War II Lwoff won the Medal of the Resistance for work in the French underground. He was also made an officer of the Legion of Honour.

Details

André Michel Lwoff (8 May 1902 – 30 September 1994) was a French microbiologist and Nobel laureate.

Education, early life and career

Lwoff was born in Ainay-le-Château, Allier, in Auvergne, France, into a Jewish family of Russian-Polish origin, the son of Marie (Siminovitch), an artist, and Solomon Lwoff, a psychiatrist. He joined the Institute Pasteur in Paris when he was 19 years old. In 1932, he finished his PhD and, with the help of a grant from the Rockefeller Foundation, moved with his wife and co-researcher Marguerite Lwoff to the Kaiser Wilhelm Institute for Medical Research of Heidelberg to Otto Meyerhof, where he did research on the development of flagellates. Another Rockefeller grant allowed him go to the University of Cambridge in 1937. In 1938, he was appointed departmental head at the Institut Pasteur, where he did groundbreaking research on bacteriophages, microbiota and on the poliovirus.

Awards and honors

He was awarded numerous prizes from the French Académie des Sciences, the Grand Prix Charles-Leopold Mayer, the Leeuwenhoek Medal of the Royal Netherlands Academy of Arts and Sciences in 1960 and the Keilin Medal of the British Biochemical Society in 1964. He was awarded a Nobel Prize in Medicine in 1965 for the discovery of the mechanism that some viruses (which he named proviruses) use to infect bacteria. He was an elected member of the United States National Academy of Sciences, the American Academy of Arts and Sciences, and the American Philosophical Society. Throughout his career he partnered with his wife Marguerite Lwoff although he gained considerably more recognition. Lwoff was elected a Foreign Member of the Royal Society in 1958. Lwoff was also president of the FEMS for a term of two years from 1974. The FEMS-Lwoff Award in microbiology is named in his honour.

Personal life

Lwoff was married to the microbiologist and virologist Marguerite Lwoff with whom he published many works. He was also a humanist against capital punishment.

2449) Benzene Hexachloride

Gist

Benzene hexachloride (BHC) was historically used as a broad-spectrum insecticide in agriculture and public health, but its use has been banned or heavily restricted in many countries due to its environmental persistence and health concerns. Its gamma isomer, lindane, was used in pharmaceuticals to treat parasitic infections like lice and scabies, and in veterinary medicine for parasites. Other limited uses have included seed treatment and as a bird repellent. 

BHC (Benzene Hexachloride) is formed through a photochlorination reaction where benzene combines with chlorine under sunlight or UV light. This free-radical addition reaction breaks the double bonds in the benzene ring, and six chlorine atoms add to the carbon atoms, resulting in a mixture of stereoisomers of 1,2,3,4,5,6-hexachlorocyclohexane. 

Summary

Lindane, also known as gamma-hexachlorocyclohexane (γ-HCH), gammaxene, Gammallin and benzene hexachloride (BHC), is an organochlorine chemical and an isomer of hexachlorocyclohexane that has been used both as an agricultural insecticide and as a pharmaceutical treatment for lice and scabies.

Lindane is a neurotoxin that interferes with GABA neurotransmitter function by interacting with the GABAA receptor-chloride channel complex at the picrotoxin binding site. In humans, lindane affects the nervous system, liver, and kidneys, and may well be a carcinogen. Whether lindane is an endocrine disruptor is unclear.

The World Health Organization classifies lindane as "moderately hazardous", and its international trade is restricted and regulated under the Rotterdam Convention on Prior Informed Consent. In 2009, the production and agricultural use of lindane was banned under the Stockholm Convention on persistent organic pollutants. A specific exemption to that ban allows it to continue to be used as a second-line pharmaceutical treatment for lice and scabies.

(GABA: GABA (gamma-aminobutyric acid, γ-aminobutyric acid) is the chief inhibitory neurotransmitter in the developmentally mature mammalian central nervous system. Its principal role is reducing neuronal excitability throughout the nervous system.)

Details

Benzene hexachloride (BHC), any of several stereoisomers of 1,2,3,4,5,6-hexachlorocyclohexane formed by the light-induced addition of chlorine to benzene. One of these isomers is an insecticide called lindane, or Gammexane.

Benzene hexachloride was first prepared in 1825; the insecticidal properties were identified in 1944 with the γ-isomer (gamma-isomer), which is about 1,000 times more toxic than any of the other diastereomers formed in the reaction. The structural differences between these individuals are in the orientations of the chlorine atoms with respect to the ring of carbon atoms.

The chemical addition of chlorine to benzene produces a mixture of several stereoisomers of 1,2,3,4,5,6-hexachlorocyclohexane. The γ-isomer, which makes up 20–25 percent of this mixture, is more soluble than the other isomers in certain solvents and can be separated from them. More volatile than DDT, BHC has a faster but less protracted action upon insects.

Lindane has been shown to accumulate in the food chain. This occurs because animals, including humans, eat foods grown in lindane-contaminated soils, and fishes and other marine life are exposed to lindane-contaminated waters. In fishes and mammals, exposure to high levels of lindane may cause acute poisoning, which is evidenced by nervous system dysfunction. Chronic exposure may adversely affect liver function in humans. Lindane’s use indoors in smoke fumigators is no longer permitted, and its use as an insecticide has been banned in many countries. Topical use in lotions to combat lice is permitted.

Additional Information

Benzene hexachloride (BHC), also known as hexachlorocyclohexane (HCH), is a colorless, crystalline solid with a musty odor. It is a chlorinated hydrocarbon that was once widely used as an insecticide. However, due to its persistence in the environment and its potential to cause health problems, BHC is now banned or restricted in many countries.

Health Effects of Benzene Hexachloride

BHC can cause a variety of health problems, including:

Acute effects: BHC can cause acute health effects such as skin irritation, eye irritation, respiratory problems, and nausea.
Chronic effects: BHC can cause chronic health effects such as liver damage, kidney damage, and cancer.
Developmental effects: BHC can cause developmental effects such as birth defects and learning disabilities.

Environmental Effects of Benzene Hexachloride

BHC is persistent in the environment and can accumulate in the food chain. It can also contaminate soil and water. BHC can be harmful to wildlife, including fish, birds, and mammals.

Regulations on Benzene Hexachloride

BHC is now banned or restricted in many countries due to its potential to cause health and environmental problems. In the United States, BHC is registered for use only as a termiticide.

Benzene hexachloride is a dangerous chemical that can cause a variety of health and environmental problems. It is important to be aware of the risks associated with BHC and to take steps to avoid exposure to this chemical.

Hi,

#10673. What does the term in Biology Endoderm mean?

#10674. What does the term in Biology Endogeny mean?

Hi,

#2529. What does the medical term Hematidrosis mean?

Hi,

#9809.

Hi,

2654.

2396) François Jacob

Gist:

Work

The biochemical processes that take place within an organism's cells are controlled by the genes found inside DNA molecules. François Jacob and Jacques Monod proved how the genetic information is converted during the formation of proteins by means of a messenger, which proved to the substance we now know as RNA. Different cells work in different ways at different times, however. This too is regulated by genes. In the early 1960s Monod and Jacob mapped the intricate processes that determine how genes are expressed or suppressed in a self-regulating process.

Summary

François Jacob (born June 17, 1920, Nancy, France—died April 19, 2013, Paris) was a French biologist who, together with André Lwoff and Jacques Monod, was awarded the 1965 Nobel Prize for Physiology or Medicine for discoveries concerning regulatory activities in bacteria.

Jacob received an M.D. degree (1947) and a doctorate in science (1954) from the University of Paris. Most of the work of Jacob, Lwoff, and Monod was carried out at the Pasteur Institute (Paris), which Jacob joined in 1950 as a research assistant. In 1960 he became head of the department of cellular genetics at the institute, and from 1965 he was also professor of cellular genetics at the Collège de France. In 1977 he became a member of the Academy of Sciences.

With a coworker at the Pasteur Institute, Jacob discovered that the genes of a bacterium are arranged linearly in a ring and that the ring can be broken at almost any point. In 1958 Monod and Jacob began to collaborate on studies of the regulation of bacterial enzyme synthesis. One of their first major contributions was the discovery of regulator genes (operons), so called because they control the activities of structural genes. The latter, in turn, not only transmit hereditary characteristics but also serve in the production of enzymes, other proteins, and ribonucleic acid (RNA).

Jacob and Monod also proposed the existence of an RNA messenger, a partial copy of the gene substance deoxyribonucleic acid (DNA), that carries genetic information to other parts of the cell. They also found that in a normal cell the balance between regulator and structural genes enables the cell to adapt to varying conditions. An interruption in this balance, however, can stimulate the production of new enzymes that can prove either beneficial or destructive to the cell. In addition to his research activities, Jacob wrote important books on the history and philosophy of the life sciences, including La Logique du vivant: une histoire de l’hérédité (1970; The Logic of Life: A History of Heredity).

Details

François Jacob (17 June 1920 – 19 April 2013) was a French biologist who, together with Jacques Monod, originated the idea that control of enzyme levels in all cells occurs through regulation of transcription. He shared the 1965 Nobel Prize in Medicine with Jacques Monod and André Lwoff.

Early years

Jacob was born the only child of Simon, a merchant, and Thérèse (Franck) Jacob, in Nancy, France. An inquisitive child, he learned to read at a young age. Albert Franck, Jacob's maternal grandfather, a four-star general, was Jacob's childhood role model. At seven he entered the Lycée Carnot, where he was schooled for the next ten years; in his autobiography, he describes his impression of it: "a cage". He was antagonized by rightist youth at the Lycée Carnot around 1934. He describes his father as a "conformist in religion", while his mother and other family members important in his childhood were secular Jews; shortly after his bar mitzvah, he became an atheist.

Though interested (and talented) in physics and mathematics, Jacob was horrified at the prospect of spending two additional years in "an even more draconian regime" to prepare for higher study at the Polytechnique. Instead, after observing a surgical operation that cemented his "slight interest" in medicine, he entered medical school.

During the German occupation of France—and on the heels of his mother's death—Jacob left France for Great Britain to join the war effort. Jacob, who had only completed his second year of medical studies, joined the medical company of the French 2nd Armored Division in 1940. He was injured in a German air attack in 1944 and returned to now-liberated Paris on 1 August 1944. For his wartime service, he was awarded France's WWII highest decoration for valor, the Cross of Liberation, as well as Légion d'honneur and croix de guerre.

After his recovery, Jacob returned to medical school and began researching tyrothricin and learning the methods of bacteriology in the process. He completed a thesis he described as "replicating American work" on the effectiveness of the antibiotic against local infections, and became a medical doctor in 1947. Though attracted to research as a career, he was discouraged by his own perceived ignorance after attending a microbiology congress that summer. Instead, he took a position at the Cabanel Center, where he had done his thesis research; his new work entailed the manufacture of an antibiotic, tyrothricin. Later, the center was contracted to convert gunpowder factories for penicillin production (though this proved impossible).

Also in this period, he met and began courting his future wife, Lise Bloch. Jacob remarried in 1999 to Geneviève Barrier.

Research

In 1961 Jacob and Monod explored the idea that the control of enzyme expression levels in cells is a result of regulation of transcription of DNA sequences. Their experiments and ideas gave impetus to the emerging field of molecular developmental biology, and of transcriptional regulation in particular.

For many years it had been known that bacterial and other cells could respond to external conditions by regulating levels of their key metabolic enzymes, and/or the activity of these enzymes. For instance, if a bacterium finds itself in a broth containing lactose, rather than the simpler sugar glucose, it must adapt itself to the need to 1) import lactose, 2) cleave lactose to its constituents glucose and galactose, and 3) convert the galactose to glucose. It was known that cells ramp up their production of the enzymes that do these steps when exposed to lactose, rather than wastefully producing these enzymes all the time. Studies of enzyme activity control were progressing through theories of the (allosteric) action of small molecules on the enzyme molecule itself (switching it on or off), but the method of controlling the enzyme production was not well understood at the time.

With the earlier determination of the structure and central importance of DNA, it became clear that all proteins were being produced in some way from its genetic code, and that this step might form a key control point. Jacob and Monod made key experimental and theoretical discoveries that demonstrated that in the case of the lactose system outlined above (in the bacterium E. coli), there are specific proteins that are devoted to repressing the transcription of the DNA to its product (RNA, which in turn is decoded into protein).

This repressor (the lac repressor) is made in all cells, binding directly to DNA at the genes it controls, and physically preventing the transcription apparatus from gaining access to the DNA. In the presence of lactose, some of the lactose is converted to allolactose, which binds to the repressor making it no longer able to bind to DNA, and the transcriptional repression is lifted. In this way, a robust feedback loop is constructed that allows the set of lactose-digesting protein products to be made only when they are needed.

Jacob and Monod extended this repressor model to all genes in all organisms in their initial exuberance. The regulation of gene activity has developed into a very large sub-discipline of molecular biology, and in truth exhibits enormous variety in mechanism and many levels of complexity. Current researchers find regulatory events at every conceivable level of the processes that express genetic information. In the relatively simple genome of baker's yeast, (Saccharomyces cerevisiae), 405 of its 6,419 protein-encoding genes are directly involved in transcriptional control, compared to 1,938 that are enzymes.