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Food preservation
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Food preservation prevents the growth of microorganisms (such as yeasts), or other microorganisms (although some methods work by introducing benign bacteria or fungi to the food), as well as slowing the oxidation of fats that cause rancidity. Food preservation may also include processes that inhibit visual deterioration, such as the enzymatic browning reaction in apples after they are cut during food preparation.
Many processes designed to preserve food involve more than one food preservation method. Preserving fruit by turning it into jam, for example, involves boiling (to reduce the fruit’s moisture content and to kill bacteria, etc.), sugaring (to prevent their re-growth) and sealing within an airtight jar (to prevent recontamination). Some traditional methods of preserving food have been shown to have a lower energy input and carbon footprint, when compared to modern methods.[1]
Some methods of food preservation are known to create carcinogens. In 2015, the International Agency for Research on Cancer of the World Health Organization classified processed meat, i.e. meat that has undergone salting, curing, fermenting, and smoking, as "carcinogenic to humans".[2][3][4]
Maintaining or creating nutritional value, texture and flavor is an important aspect of food preservation.
Contents
[hide]
1 Traditional techniques
1.1 Curing
1.2 Cooling
1.3 Freezing
1.4 Boiling
1.5 Heating
1.6 Sugaring
1.7 Pickling
1.8 Lye
1.9 Canning
1.10 Jellying
1.11 Jugging
1.12 Burial
1.13 Fermentation
2 Modern industrial techniques
2.1 Pasteurization
2.2 Vacuum packing
2.3 Artificial food additives
2.4 Irradiation
2.5 Pulsed electric field electroporation
2.6 Modified atmosphere
2.7 Nonthermal plasma
2.8 High-pressure food preservation
2.9 Biopreservation
2.10 Hurdle technology
3 See also
4 Notes
5 References
6 Further reading
7 External links
Traditional techniques
New techniques of food preservation became available to the home chef from the dawn of agriculture until the Industrial Revolution.
Curing
Bag of Prague powder #1, also known as "curing salt" or "pink salt". It is typically a combination of salt and sodium nitrite, with the pink color added to distinguish it from ordinary salt.
Main article: Curing (food preservation)
The earliest form of curing was dehydration or drying, used as early as 12,000 BC. Smoking and salting techniques improve on the drying process and add antimicrobial agents that aid in preservation. Smoke deposits a number of pyrolysis products onto the food, including the phenols syringol, guaiacol and catechol.[5] Salt accelerates the drying process using osmosis and also inhibits the growth of several common strains of bacteria. More recently nitrites have been used to cure meat, contributing a characteristic pink colour.[6]
Cooling
Main article: Refrigeration
Cooling preserves food by slowing down the growth and reproduction of microorganisms and the action of enzymes that causes the food to rot. The introduction of commercial and domestic refrigerators drastically improved the diets of many in the Western world by allowing food such as fresh fruit, salads and dairy products to be stored safely for longer periods, particularly during warm weather.
Before the era of mechanical refrigeration, cooling for food storage occurred in the forms of root cellars and iceboxes. Rural people often did their own ice cutting, whereas town and city dwellers often relied on the ice trade. Today, root cellaring remains popular among people who value various goals, including local food, heirloom crops, traditional home cooking techniques, family farming, frugality, self-sufficiency, organic farming, and others.
Freezing
Main article: Frozen food
Freezing is also one of the most commonly used processes, both commercially and domestically, for preserving a very wide range of foods, including prepared foods that would not have required freezing in their unprepared state. For example, potato waffles are stored in the freezer, but potatoes themselves require only a cool dark place to ensure many months' storage. Cold stores provide large-volume, long-term storage for strategic food stocks held in case of national emergency in many countries.
Boiling
Main article: Boiling
Boiling liquid food items can kill any existing microbes. Milk and water are often boiled to kill any harmful microbes that may be present in them.
Heating
Heating to temperatures which are sufficient to kill microorganisms inside the food is a method used with perpetual stews. Milk is also boiled before storing to kill many microorganisms.
Sugaring
See also: Sugaring
The earliest cultures have used sugar as a preservative, and it was commonplace to store fruit in honey. Similar to pickled foods, sugar cane was brought to Europe through the trade routes. In northern climates without sufficient sun to dry foods, preserves are made by heating the fruit with sugar.[7] "Sugar tends to draw water from the microbes (plasmolysis). This process leaves the microbial cells dehydrated, thus killing them. In this way, the food will remain safe from microbial spoilage."[5] Sugar is used to preserve fruits, either in an antimicrobial syrup with fruit such as apples, pears, peaches, apricots, and plums, or in crystallized form where the preserved material is cooked in sugar to the point of crystallization and the resultant product is then stored dry. This method is used for the skins of citrus fruit (candied peel), angelica, and ginger. Also, sugaring can be used in the production of jam and jelly.
Pickling
Main article: Pickling
Pickling is a method of preserving food in an edible, antimicrobial liquid. Pickling can be broadly classified into two categories: chemical pickling and fermentation pickling.
In chemical pickling, the food is placed in an edible liquid that inhibits or kills bacteria and other microorganisms. Typical pickling agents include brine (high in salt), vinegar, alcohol, and vegetable oil. Many chemical pickling processes also involve heating or boiling so that the food being preserved becomes saturated with the pickling agent. Common chemically pickled foods include cucumbers, peppers, corned beef, herring, and eggs, as well as mixed vegetables such as piccalilli.
In fermentation pickling, bacteria in the liquid produce organic acids as preservation agents, typically by a process that produces lactic acid through the presence of lactobacillales. Fermented pickles include sauerkraut, nukazuke, kimchi, and surströmming.
Lye
Main article: Sodium hydroxide § Food preparation
Sodium hydroxide (lye) makes food too alkaline for bacterial growth. Lye will saponify fats in the food, which will change its flavor and texture. Lutefisk uses lye in its preparation, as do some olive recipes. Modern recipes for century eggs also call for lye.
Canning
Preserved food
Main article: Canning
See also: Home canning
Canning involves cooking food, sealing it in sterilized cans or jars, and boiling the containers to kill or weaken any remaining bacteria as a form of sterilization. It was invented by the French confectioner Nicolas Appert.[8] By 1806, this process was used by the French Navy to preserve meat, fruit, vegetables, and even milk. Although Appert had discovered a new way of preservation, it wasn't understood until 1864 when Louis Pasteur found the relationship between microorganisms, food spoilage, and illness.[7]
Foods have varying degrees of natural protection against spoilage and may require that the final step occur in a pressure cooker. High-acid fruits like strawberries require no preservatives to can and only a short boiling cycle, whereas marginal vegetables such as carrots require longer boiling and addition of other acidic elements. Low-acid foods, such as vegetables and meats, require pressure canning. Food preserved by canning or bottling is at immediate risk of spoilage once the can or bottle has been opened.
Lack of quality control in the canning process may allow ingress of water or micro-organisms. Most such failures are rapidly detected as decomposition within the can causes gas production and the can will swell or burst. However, there have been examples of poor manufacture (underprocessing) and poor hygiene allowing contamination of canned food by the obligate anaerobe Clostridium botulinum, which produces an acute toxin within the food, leading to severe illness or death. This organism produces no gas or obvious taste and remains undetected by taste or smell. Its toxin is denatured by cooking, however. Cooked mushrooms, handled poorly and then canned, can support the growth of Staphylococcus aureus, which produces a toxin that is not destroyed by canning or subsequent reheating.
Jellying
Main article: Aspic
See also: Potted shrimps and Confit
Food may be preserved by cooking in a material that solidifies to form a gel. Such materials include gelatin, agar, maize flour, and arrowroot flour. Some foods naturally form a protein gel when cooked, such as eels and elvers, and sipunculid worms, which are a delicacy in Xiamen, in the Fujian province of the People's Republic of China. Jellied eels are a delicacy in the East End of London, where they are eaten with mashed potatoes. Potted meats in aspic (a gel made from gelatin and clarified meat broth) were a common way of serving meat off-cuts in the UK until the 1950s. Many jugged meats are also jellied.
A traditional British way of preserving meat (particularly shrimp) is by setting it in a pot and sealing it with a layer of fat. Also common is potted chicken liver; jellying is one of the steps in producing traditional pâtés.
Jugging
Main article: Jugging
Meat can be preserved by jugging. Jugging is the process of stewing the meat (commonly game or fish) in a covered earthenware jug or casserole. The animal to be jugged is usually cut into pieces, placed into a tightly-sealed jug with brine or gravy, and stewed. Red wine and/or the animal's own blood is sometimes added to the cooking liquid. Jugging was a popular method of preserving meat up until the middle of the 20th century.
Burial
Burial of food can preserve it due to a variety of factors: lack of light, lack of oxygen, cool temperatures, pH level, or desiccants in the soil. Burial may be combined with other methods such as salting or fermentation. Most foods can be preserved in soil that is very dry and salty (thus a desiccant) such as sand, or soil that is frozen.
Many root vegetables are very resistant to spoilage and require no other preservation than storage in cool dark conditions, for example by burial in the ground, such as in a storage clamp. Century eggs are traditionally created by placing eggs in alkaline mud (or other alkaline substance), resulting in their "inorganic" fermentation through raised pH instead of spoiling. The fermentation preserves them and breaks down some of the complex, less flavorful proteins and fats into simpler, more flavorful ones. Cabbage was traditionally buried during Autumn in northern US farms for preservation. Some methods keep it crispy while other methods produce sauerkraut.[citation needed] A similar process is used in the traditional production of kimchi. Sometimes meat is buried under conditions that cause preservation. If buried on hot coals or ashes, the heat can kill pathogens, the dry ash can desiccate, and the earth can block oxygen and further contamination. If buried where the earth is very cold, the earth acts like a refrigerator. Before burial, meat (pig/boar) can be fatted. The tallow of the animal is heated and poured over meat in a barrel. Once the fat hardens the barrel is sealed and buried in a cold cellar or ground.
In Orissa, India, it is practical to store rice by burying it underground. This method helps to store for three to six months during the dry season.
Butter and similar substances have been preserved as bog butter in Irish peat bogs for centuries.
Fermentation
See also: Fermentation (food)
Some foods, such as many cheeses, wines, and beers, use specific micro-organisms that combat spoilage from other less-benign organisms. These micro-organisms keep pathogens in check by creating an environment toxic for themselves and other micro-organisms by producing acid or alcohol. Methods of fermentation include, but are not limited to, starter micro-organisms, salt, hops, controlled (usually cool) temperatures and controlled (usually low) levels of oxygen. These methods are used to create the specific controlled conditions that will support the desirable organisms that produce food fit for human consumption.
Fermentation is the microbial conversion of starch and sugars into alcohol. Not only can fermentation produce alcohol, but it can also be a valuable preservation technique. Fermentation can also make foods more nutritious and palatable. For example, drinking water in the Middle Ages was dangerous because it often contained pathogens that could spread disease. When the water is made into beer, the boiling during the brewing process kills any bacteria in the water that could make people sick. Additionally, the water now has the nutrients from the barley and other ingredients, and the microorganisms can also produce vitamins as they ferment.[7]
Modern industrial techniques
Techniques of food preservation were developed in research laboratories for commercial applications.
Pasteurization
Main article: Pasteurization
Pasteurization is a process for preservation of liquid food. It was originally applied to combat the souring of young local wines. Today, the process is mainly applied to dairy products. In this method, milk is heated at about 70 °C (158 °F) for 15–30 seconds to kill the bacteria present in it and cooling it quickly to 10 °C (50 °F) to prevent the remaining bacteria from growing. The milk is then stored in sterilized bottles or pouches in cold places. This method was invented by Louis Pasteur, a French chemist, in 1862.
Vacuum packing
Main article: Vacuum packing
Vacuum-packing stores food in a vacuum environment, usually in an air-tight bag or bottle. The vacuum environment strips bacteria of oxygen needed for survival. Vacuum-packing is commonly used for storing nuts to reduce loss of flavor from oxidization. A major drawback to vacuum packaging, at the consumer level, is that vacuum sealing can deform contents and rob certain foods, such as cheese, of its flavor.
Artificial food additives
Main article: Preservatives
Preservative food additives can be antimicrobial—which inhibit the growth of bacteria or fungi, including mold—or antioxidant, such as oxygen absorbers, which inhibit the oxidation of food constituents. Common antimicrobial preservatives include calcium propionate, sodium nitrate, sodium nitrite, sulfites (sulfur dioxide, sodium bisulfite, potassium hydrogen sulfite, etc.), and EDTA. Antioxidants include butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). Other preservatives include formaldehyde (usually in solution), glutaraldehyde (insecticide), ethanol, and methylchloroisothiazolinone.
Irradiation
Main article: Food irradiation
Irradiation of food[9] is the exposure of food to ionizing radiation. The two types of ionizing radiation used are beta particles (high-energy electrons) and gamma rays (emitted from radioactive sources such as cobalt-60 or cesium-137). Treatment effects include killing bacteria, molds, and insect pests, reducing the ripening and spoiling of fruits, and at higher doses inducing sterility. The technology may be compared to pasteurization; it is sometimes called "cold pasteurization", as the product is not heated.
The irradiation process is not directly related to nuclear energy, but does use radioactive isotopes produced in nuclear reactors. Cobalt-60, for example does not occur naturally and can only be produced through neutron bombardment of cobalt-59. Ionizing radiation at high energy levels is hazardous to life (hence its usefulness in sterilisation); for this reason, irradiation facilities have a heavily shielded irradiation room where the process takes place. Radiation safety procedures are used to ensure that neither the workers in such facilities nor the environment receives any radiation dose above administrative limits. Irradiated food does not and cannot become radioactive, and national and international expert bodies have declared food irradiation as wholesome.[10][11] However, the wholesomeness of consuming such food is disputed by opponents[12] and consumer organizations.[13] National and international expert bodies have declared food irradiation as "wholesome"; organizations of the United Nations, such as the World Health Organization and Food and Agriculture Organization, endorse food irradiation. International legislation on whether food may be irradiated or not varies worldwide from no regulation to full banning.[14] Irradiation may allow lower-quality or contaminated foods to be rendered marketable.
Approximately 500,000 tons of food items are irradiated per year worldwide in over 40 countries. These are mainly spices and condiments with an increasing segment of fresh fruit irradiated for fruit fly quarantine.[15][16]
Pulsed electric field electroporation
Main article: Electroporation
Pulsed electric field (PEF) electroporation is a method for processing cells by means of brief pulses of a strong electric field. PEF holds potential as a type of low-temperature alternative pasteurization process for sterilizing food products. In PEF processing, a substance is placed between two electrodes, then the pulsed electric field is applied. The electric field enlarges the pores of the cell membranes, which kills the cells and releases their contents. PEF for food processing is a developing technology still being researched. There have been limited industrial applications of PEF processing for the pasteurization of fruit juices. To date, several PEF treated juices are available on the market in Europe. Furthermore, for several years a juice pasteurization application in the US has used PEF. For cell disintegration purposes especially potato processors show great interest in PEF technology as an efficient alternative for their preheaters. Potato applications are already operational in the US and Canada. There are also commercial PEF potato applications in various countries in Europe, as well as in Australia, India, and China.[17]
Modified atmosphere
Main article: Modified atmosphere
Modifying atmosphere is a way to preserve food by operating on the atmosphere around it. Salad crops that are notoriously difficult to preserve are now being packaged in sealed bags with an atmosphere modified to reduce the oxygen (O2) concentration and increase the carbon dioxide (CO2) concentration. There is concern that, although salad vegetables retain their appearance and texture in such conditions, this method of preservation may not retain nutrients, especially vitamins. There are two methods for preserving grains with carbon dioxide. One method is placing a block of dry ice in the bottom and filling the can with the grain. Another method is purging the container from the bottom by gaseous carbon dioxide from a cylinder or bulk supply vessel.
Carbon dioxide prevents insects and, depending on concentration, mold and oxidation from damaging the grain. Grain stored in this way can remain edible for approximately five years.[18]
Nitrogen gas (N2) at concentrations of 98% or higher is also used effectively to kill insects in the grain through hypoxia.[19] However, carbon dioxide has an advantage in this respect, as it kills organisms through hypercarbia and hypoxia (depending on concentration), but it requires concentrations of above 35%,[20] or so. This makes carbon dioxide preferable for fumigation in situations where a hermetic seal cannot be maintained.
Controlled Atmospheric Storage (CA): "CA storage is a non-chemical process. Oxygen levels in the sealed rooms are reduced, usually by the infusion of nitrogen gas, from the approximate 21 percent in the air we breathe to 1 percent or 2 percent. Temperatures are kept at a constant 0–2 °C (32–36 °F). Humidity is maintained at 95 percent and carbon dioxide levels are also controlled. Exact conditions in the rooms are set according to the apple variety. Researchers develop specific regimens for each variety to achieve the best quality. Computers help keep conditions constant." "Eastern Washington, where most of Washington’s apples are grown, has enough warehouse storage for 181 million boxes of fruit, according to a report done in 1997 by managers for the Washington State Department of Agriculture Plant Services Division. The storage capacity study shows that 67 percent of that space—enough for 121,008,000 boxes of apples—is CA storage." [21]
Air-tight storage of grains (sometimes called hermetic storage) relies on the respiration of grain, insects, and fungi that can modify the enclosed atmosphere sufficiently to control insect pests. This is a method of great antiquity,[22] as well as having modern equivalents. The success of the method relies on having the correct mix of sealing, grain moisture, and temperature.[23]
A patented process uses fuel cells to exhaust and automatically maintain the exhaustion of oxygen in a shipping container, containing, for example, fresh fish.[24]
Nonthermal plasma
Main article: Nonthermal plasma
This process subjects the surface of food to a "flame" of ionized gas molecules, such as helium or nitrogen. This causes micro-organisms to die off on the surface.[25]
High-pressure food preservation
Main article: Pascalization
High-pressure food preservation or pascalization refers to the use of a food preservation technique that makes use of high pressure. "Pressed inside a vessel exerting 70,000 pounds per square inch (480 MPa) or more, food can be processed so that it retains its fresh appearance, flavor, texture and nutrients while disabling harmful microorganisms and slowing spoilage." By 2005, the process was being used for products ranging from orange juice to guacamole to deli meats and widely sold.[26]
Biopreservation
3D stick model of nisin. Some lactic acid bacteria manufacture nisin. It is a particularly effective preservative.
Main article: Biopreservation
Biopreservation is the use of natural or controlled microbiota or antimicrobials as a way of preserving food and extending its shelf life.[27] Beneficial bacteria or the fermentation products produced by these bacteria are used in biopreservation to control spoilage and render pathogens inactive in food.[28] It is a benign ecological approach which is gaining increasing attention.[27]
Of special interest are lactic acid bacteria (LAB). Lactic acid bacteria have antagonistic properties that make them particularly useful as biopreservatives. When LABs compete for nutrients, their metabolites often include active antimicrobials such as lactic acid, acetic acid, hydrogen peroxide, and peptide bacteriocins. Some LABs produce the antimicrobial nisin, which is a particularly effective preservative.[29][30]
These days, LAB bacteriocins are used as an integral part of hurdle technology. Using them in combination with other preservative techniques can effectively control spoilage bacteria and other pathogens, and can inhibit the activities of a wide spectrum of organisms, including inherently resistant Gram-negative bacteria.[27]
Hurdle technology
Main article: Hurdle technology
Hurdle technology is a method of ensuring that pathogens in food products can be eliminated or controlled by combining more than one approach. These approaches can be thought of as "hurdles" the pathogen has to overcome if it is to remain active in the food. The right combination of hurdles can ensure all pathogens are eliminated or rendered harmless in the final product.[31]
Hurdle technology has been defined by Leistner (2000) as an intelligent combination of hurdles that secures the microbial safety and stability as well as the organoleptic and nutritional quality and the economic viability of food products.[32] The organoleptic quality of the food refers to its sensory properties, that is its look, taste, smell, and texture.
Examples of hurdles in a food system are high temperature during processing, low temperature during storage, increasing the acidity, lowering the water activity or redox potential, and the presence of preservatives or biopreservatives. According to the type of pathogens and how risky they are, the intensity of the hurdles can be adjusted individually to meet consumer preferences in an economical way, without sacrificing the safety of the product.[31]
Principal hurdles used for food preservation (after Leistner, 1995)[33][34]
Parameter
Symbol
Application
High temperature F Heating
Low temperature T Chilling, freezing
Reduced water activity aw Drying, curing, conserving
Increased acidity pH Acid addition or formation
Reduced redox potential Eh Removal of oxygen or addition of ascorbate
Biopreservatives Competitive flora such as microbial fermentation
Other preservatives Sorbates, sulfites, nitrites
See also
Food portal
Blast chilling
Food engineering
Food microbiology
Food packaging
Food rheology
Food science
Food spoilage
Freeze-drying
Fresherized
List of dried foods
List of pickled foods
List of smoked foods
Refrigerate after opening
Shelf life
Notes
Jump up ^ "Preserving Food without Freezing or Canning, Chelsea Green Publishing, 1999"
Jump up ^ Stacy Simon (October 26, 2015). "World Health Organization Says Processed Meat Causes Cancer". Cancer.org.
Jump up ^ James Gallagher (26 October 2015). "Processed meats do cause cancer - WHO". BBC.
Jump up ^ "IARC Monographs evaluate consumption of red meat and processed meat" (PDF). International Agency for Research on Cancer. 26 October 2015.
^ Jump up to: a b Msagati, T. (2012). "The Chemistry of Food Additives and Preservatives"
Jump up ^ Nummer, Brian; Andress, Elizabeth (June 2015). "Curing and Smoking Meats for Home Food Preservation". National Center for Home Food Preservation.
^ Jump up to: a b c Nummer, B. (2002). "Historical Origins of Food Preservation" http://nchfp.uga.edu/publications/nchfp/factsheets/food_pres_hist.html. (Accessed on May 5, 2014)
Jump up ^ Nicolas Appert inventeur et humaniste by Jean-Paul Barbier, Paris, 1994 and http://www.appert-aina.com
Jump up ^ anon., Food Irradation – A technique for preserving and improving the safety of food, WHO, Geneva, 1991
Jump up ^ World Health Organization. Wholesomeness of irradiated food. Geneva, Technical Report Series No. 659, 1981
Jump up ^ World Health Organization. High-Dose Irradiation: Wholesomeness of Food Irradiated With Doses Above 10 kGy. Report of a Joint FAO/IAEA/WHO Study Group. Geneva, Switzerland: World Health Organization; 1999. WHO Technical Report Series No. 890
Jump up ^ Hauther, W. & Worth, M., Zapped! Irradiation and the Death of Food, Food & Water Watch Press, Washington, DC, 2008
Jump up ^ Consumers International – Home Archived 18 August 2010 at the Wayback Machine.
Jump up ^ NUCLEUS – Food Irradiation Clearances Archived 26 May 2008 at the Wayback Machine.
Jump up ^ Food irradiation – Position of ADA J Am Diet Assoc. 2000;100:246-253 Archived 16 February 2016 at the Wayback Machine.
Jump up ^ C.M. Deeley, M. Gao, R. Hunter, D.A.E. Ehlermann, The development of food irradiation in the Asia Pacific, the Americas and Europe; tutorial presented to the International Meeting on Radiation Processing, Kuala Lumpur, 2006. http://www.doubleia.org/index.php?sectionid=43&parentid=13&contentid=494
Jump up ^ "Elea Pulsed Electric Field Technology - Homepage". www.elea-technology.com. Retrieved 2017-03-02.
Jump up ^ Navarro, Shlomo; Timlick, Blaine; Demianyk, Colin; White, Noel (March 2012). "Controlled or Modified Atmospheres" (PDF). k-state.edu. Retrieved March 17, 2018.
Jump up ^ Annis, P.C. and Dowsett, H.A. 1993. Low oxygen disinfestation of grain: exposure periods needed for high mortality. Proc. International Conference on Controlled Atmosphere and Fumigation. Winnipeg, June 1992, Caspit Press, Jerusalem, pp 71-83.
Jump up ^ Annis, P.C. and Morton, R. 1997. The acute mortality effects of carbon dioxide on various life stages of Sitophilus oryzae. J. Stored Prod.Res. 33. 115-124
Jump up ^ Controlled Atmospheric Storage (CA) :: Washington State Apple Commission
Jump up ^ Various authors, Session 1: Natural Air-Tight Storage In: Shejbal, J., ed., Controlled Atmosphere Storage of Grains, Elsevier: Amsterdam, 1-33
Jump up ^ Annis P.C. and Banks H.J. 1993. Is hermetic storage of grains feasible in modern agricultural systems? In "Pest control and sustainable agriculture" Eds S.A. Corey, D.J. Dall and W.M. Milne. CSIRO, Australia. 479-482
Jump up ^ Laine Welch (18 May 2013). "Laine Welch: Fuel cell technology boosts long-distance fish shipping". Anchorage Daily News. Archived from the original on 9 June 2013. Retrieved May 19, 2013.
Jump up ^ NWT magazine, December 2012
Jump up ^ "High-Pressure Processing Keeps Food Safe". Military.com. Archived from the original on 2008-02-02. Retrieved 2008-12-16. Pressed inside a vessel exerting 70,000 pounds per square inch or more, food can be processed so that it retains its fresh appearance, flavor, texture and nutrients while disabling harmful microorganisms and slowing spoilage.
^ Jump up to: a b c Ananou S, Maqueda M, Martínez-Bueno M and Valdivia E (2007) "Biopreservation, an ecological approach to improve the safety and shelf-life of foods" In: A. Méndez-Vilas (Ed.) Communicating Current Research and Educational Topics and Trends in Applied Microbiology, Formatex. ISBN 978-84-611-9423-0.
Jump up ^ Yousef AE and Carolyn Carlstrom C (2003) Food microbiology: a laboratory manual Wiley, Page 226. ISBN 978-0-471-39105-0.
Jump up ^ FAO: Preservation techniques Fisheries and aquaculture department, Rome. Updated 27 May 2005. Retrieved 14 March 2011.
Jump up ^ Alzamora SM, Tapia MS and López-Malo A (2000) Minimally processed fruits and vegetables: fundamental aspects and applications Springer, Page 266. ISBN 978-0-8342-1672-3.
^ Jump up to: a b Alasalvar C (2010) Seafood Quality, Safety and Health Applications John Wiley and Sons, Page 203. ISBN 978-1-4051-8070-2.
Jump up ^ Leistner I (2000) "Basic aspects of food preservation by hurdle technology" International Journal of Food Microbiology, 55:181–186.
Jump up ^ Leistner L (1995) "Principles and applications of hurdle technology" In Gould GW (Ed.) New Methods of Food Preservation, Springer, pp. 1-21. ISBN 978-0-8342-1341-8.
Jump up ^ Lee S (2004) "Microbial Safety of Pickled Fruits and Vegetables and Hurdle Technology" Internet Journal of Food Safety, 4: 21–32.
References
Riddervold, Astri. Food Conservation. ISBN 978-0-907325-40-6.
Abakarov, Nunes. "Thermal food processing optimization: algorithms and software" (PDF). Food Engineering.
Abakarov, Sushkov, Mascheroni. "Multi-criteria optimization and decision-making approach for improving of food engineering processes" (PDF). International Journal of Food Studies.
Further reading
Marx de Salcedo, Anastacia (2015). Combat-ready Kitchen: How the U.S. military shapes the way you eat. New York: Current/Penguin. ISBN 9781101601648.
External links
Wikimedia Commons has media related to Food preservation.
A ca. 1894 Gustav Hammer & Co. commercial cooking machinery catalogue.
Preserving foods ~ from the Clemson Extension Home and Garden Information Center
National Center for Home Food Preservation
BBC News Online – US army food... just add urine
Home Economics Archive: Tradition, Research, History (HEARTH)
An e-book collection of over 1,000 classic books on home economics spanning 1850 to 1950, created by Cornell University's Mann Library.
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Transcription (biology)
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For the journal, see Transcription (journal).
For transcription in eukaryotes, see Eukaryotic transcription.
Simplified diagram of mRNA synthesis and processing. Enzymes not shown.
Transcription is the first step of gene expression, in which a particular segment of DNA is copied into RNA (especially mRNA) by the enzyme RNA polymerase. Both DNA and RNA are nucleic acids, which use base pairs of nucleotides as a complementary language. During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, antiparallel RNA strand called a primary transcript.
Transcription proceeds in the following general steps:
RNA polymerase, together with one or more general transcription factors, binds to promoter DNA.
RNA polymerase creates a transcription bubble, which separates the two strands of the DNA helix. This is done by breaking the hydrogen bonds between complementary DNA nucleotides.
RNA polymerase adds RNA nucleotides (which are complementary to the nucleotides of one DNA strand).
RNA sugar-phosphate backbone forms with assistance from RNA polymerase to form an RNA strand.
Hydrogen bonds of the RNA–DNA helix break, freeing the newly synthesized RNA strand.
If the cell has a nucleus, the RNA may be further processed. This may include polyadenylation, capping, and splicing.
The RNA may remain in the nucleus or exit to the cytoplasm through the nuclear pore complex.
The stretch of DNA transcribed into an RNA molecule is called a transcription unit and encodes at least one gene. If the gene encodes a protein, the transcription produces messenger RNA (mRNA); the mRNA, in turn, serves as a template for the protein's synthesis through translation. Alternatively, the transcribed gene may encode for either non-coding RNA (such as microRNA), ribosomal RNA (rRNA), transfer RNA (tRNA), or other enzymatic RNA molecules called ribozymes.[1] Overall, RNA helps synthesize, regulate, and process proteins; it therefore plays a fundamental role in performing functions within a cell.
In virology, the term may also be used when referring to mRNA synthesis from an RNA molecule (i.e., RNA replication). For instance, the genome of a negative-sense single-stranded RNA (ssRNA -) virus may be template for a positive-sense single-stranded RNA (ssRNA +). This is because the positive-sense strand contains the information needed to translate the viral proteins for viral replication afterwards. This process is catalyzed by a viral RNA replicase.[2]
Contents
[hide]
1 Background
2 Major steps
2.1 Initiation
2.2 Promoter escape
2.3 Elongation
2.4 Termination
3 Inhibitors
4 Endogenous inhibitors
5 Transcription factories
6 History
7 Measuring and detecting
8 Reverse transcription
9 See also
10 References
11 External links
Background[edit]
A DNA transcription unit encoding for a protein may contain both a coding sequence, which will be translated into the protein, and regulatory sequences, which direct and regulate the synthesis of that protein. The regulatory sequence before ("upstream" from) the coding sequence is called the five prime untranslated region (5'UTR); the sequence after ("downstream" from) the coding sequence is called the three prime untranslated region (3'UTR).[1]
As opposed to DNA replication, transcription results in an RNA complement that includes the nucleotide uracil (U) in all instances where thymine (T) would have occurred in a DNA complement.
Only one of the two DNA strands serve as a template for transcription. The antisense strand of DNA is read by RNA polymerase from the 3' end to the 5' end during transcription (3' → 5'). The complementary RNA is created in the opposite direction, in the 5' → 3' direction, matching the sequence of the sense strand with the exception of switching uracil for thymine. This directionality is because RNA polymerase can only add nucleotides to the 3' end of the growing mRNA chain. This use of only the 3' → 5' DNA strand eliminates the need for the Okazaki fragments that are seen in DNA replication.[1] This also removes the need for an RNA primer to initiate RNA synthesis, as is the case in DNA replication.
The non-template (sense) strand of DNA is called the coding strand, because its sequence is the same as the newly created RNA transcript (except for the substitution of uracil for thymine). This is the strand that is used by convention when presenting a DNA sequence.[3]
Transcription has some proofreading mechanisms, but they are fewer and less effective than the controls for copying DNA; therefore, transcription has a lower copying fidelity than DNA replication.[4]
Major steps[edit]
Further information: Bacterial transcription and Eukaryotic transcription
Transcription is divided into initiation, promoter escape, elongation, and termination.[5]
Initiation[edit]
Transcription begins with the binding of RNA polymerase, together with one or more general transcription factor, to a specific DNA sequence referred to as a "promoter" to form an RNA polymerase-promoter "closed complex". In the "closed complex" the promoter DNA is still fully double-stranded.[5]
RNA polymerase, assisted by one or more general transcription factors, then unwinds approximately 14 base pairs of DNA to form an RNA polymerase-promoter "open complex". In the "open complex" the promoter DNA is partly unwound and single-stranded. The exposed, single-stranded DNA is referred to as the "transcription bubble."[5]
RNA polymerase, assisted by one or more general transcription factors, then selects a transcription start site in the transcription bubble, binds to an initiating NTP and an extending NTP (or a short RNA primer and an extending NTP) complementary to the transcription start site sequence, and catalyzes bond formation to yield an initial RNA product.[5]
In bacteria, RNA polymerase holoenzyme consists of five subunits: 2 α subunits, 1 β subunit, 1 β' subunit, and 1 ω subunit. In bacteria, there is one general RNA transcription factor: sigma. RNA polymerase core enzyme binds to the bacterial general transcription factor sigma to form RNA polymerase holoenzyme and then binds to a promoter.[5] ( RNA polymerase is called a holoenzyme when sigma subunit is attached to the core enzyme which is consist of 2 α subunits, 1 β subunit, 1 β' subunit only )
In archaea and eukaryotes, RNA polymerase contains subunits homologous to each of the five RNA polymerase subunits in bacteria and also contains additional subunits. In archaea and eukaryotes, the functions of the bacterial general transcription factor sigma are performed by multiple general transcription factors that work together.[5] In archaea, there are three general transcription factors: TBP, TFB, and TFE. In eukaryotes, in RNA polymerase II-dependent transcription, there are six general transcription factors: TFIIA, TFIIB (an ortholog of archaeal TFB), TFIID (a multisubunit factor in which the key subunit, TBP, is an ortholog of archaeal TBP), TFIIE (an ortholog of archaeal TFE), TFIIF, and TFIIH. In archaea and eukaryotes, the RNA polymerase-promoter closed complex is usually referred to as the "preinitiation complex."[6]
Transcription initiation is regulated by additional proteins, known as activators and repressors, and, in some cases, associated coactivators or corepressors, which modulate formation and function of the transcription initiation complex.[5]
Promoter escape[edit]
After the first bond is synthesized, the RNA polymerase must escape the promoter. During this time there is a tendency to release the RNA transcript and produce truncated transcripts. This is called abortive initiation, and is common for both eukaryotes and prokaryotes.[7] Abortive initiation continues to occur until an RNA product of a threshold length of approximately 10 nucleotides is synthesized, at which point promoter escape occurs and a transcription elongation complex is formed.
Mechanistically, promoter escape occurs through DNA scrunching, providing the energy needed to break interactions between RNA polymerase holoenzyme and the promoter.[8]
In bacteria, upon and following promoter clearance, the σ factor is released according to a stochastic model.[9]
In eukaryotes, at an RNA polymerase II-dependent promoter, upon promoter clearance, TFIIH phosphorylates serine 5 on the carboxy terminal domain of RNA polymerase II, leading to the recruitment of capping enzyme (CE).[10][11] The exact mechanism of how CE induces promoter clearance in eukaryotes is not yet known.
Elongation[edit]
Simple diagram of transcription elongation
One strand of the DNA, the template strand (or noncoding strand), is used as a template for RNA synthesis. As transcription proceeds, RNA polymerase traverses the template strand and uses base pairing complementarity with the DNA template to create an RNA copy. Although RNA polymerase traverses the template strand from 3' → 5', the coding (non-template) strand and newly formed RNA can also be used as reference points, so transcription can be described as occurring 5' → 3'. This produces an RNA molecule from 5' → 3', an exact copy of the coding strand (except that thymines are replaced with uracils, and the nucleotides are composed of a ribose (5-carbon) sugar where DNA has deoxyribose (one fewer oxygen atom) in its sugar-phosphate backbone).[citation needed]
mRNA transcription can involve multiple RNA polymerases on a single DNA template and multiple rounds of transcription (amplification of particular mRNA), so many mRNA molecules can be rapidly produced from a single copy of a gene.[citation needed] The characteristic elongation rates in prokaryotes and eukaryotes are about 10-100nts/sec.[12]
Elongation also involves a proofreading mechanism that can replace incorrectly incorporated bases. In eukaryotes, this may correspond with short pauses during transcription that allow appropriate RNA editing factors to bind. These pauses may be intrinsic to the RNA polymerase or due to chromatin structure.[citation needed]
Termination[edit]
Main article: Terminator (genetics)
Bacteria use two different strategies for transcription termination – Rho-independent termination and Rho-dependent termination. In Rho-independent transcription termination, RNA transcription stops when the newly synthesized RNA molecule forms a G-C-rich hairpin loop followed by a run of Us. When the hairpin forms, the mechanical stress breaks the weak rU-dA bonds, now filling the DNA–RNA hybrid. This pulls the poly-U transcript out of the active site of the RNA polymerase, terminating transcription. In the "Rho-dependent" type of termination, a protein factor called "Rho" destabilizes the interaction between the template and the mRNA, thus releasing the newly synthesized mRNA from the elongation complex.[13]
Transcription termination in eukaryotes is less well understood than in bacteria, but involves cleavage of the new transcript followed by template-independent addition of adenines at its new 3' end, in a process called polyadenylation.[14]
Inhibitors[edit]
Transcription inhibitors can be used as antibiotics against, for example, pathogenic bacteria (antibacterials) and fungi (antifungals). An example of such an antibacterial is rifampicin, which inhibits Bacterial transcription of DNA into mRNA by inhibiting DNA-dependent RNA polymerase by binding its beta-subunit. 8-Hydroxyquinoline is an antifungal transcription inhibitor.[15] The effects of histone methylation may also work to inhibit the action of transcription.
Endogenous inhibitors[edit]
Main article: Regulation of transcription in cancer
In vertebrates, the majority of gene promoters contain a CpG island with numerous CpG sites.[16] When many of a gene's promoter CpG sites are methylated the gene becomes inhibited (silenced).[17] Colorectal cancers typically have 3 to 6 driver mutations and 33 to 66 hitchhiker or passenger mutations.[18] However, transcriptional inhibition (silencing) may be of more importance than mutation in causing progression to cancer. For example, in colorectal cancers about 600 to 800 genes are transcriptionally inhibited by CpG island methylation (see regulation of transcription in cancer). Transcriptional repression in cancer can also occur by other epigenetic mechanisms, such as altered expression of microRNAs.[19] In breast cancer, transcriptional repression of BRCA1 may occur more frequently by over-expressed microRNA-182 than by hypermethylation of the BRCA1 promoter (see Low expression of BRCA1 in breast and ovarian cancers).
Transcription factories[edit]
Main article: Transcription factories
Active transcription units are clustered in the nucleus, in discrete sites called transcription factories or euchromatin. Such sites can be visualized by allowing engaged polymerases to extend their transcripts in tagged precursors (Br-UTP or Br-U) and immuno-labeling the tagged nascent RNA. Transcription factories can also be localized using fluorescence in situ hybridization or marked by antibodies directed against polymerases. There are ~10,000 factories in the nucleoplasm of a HeLa cell, among which are ~8,000 polymerase II factories and ~2,000 polymerase III factories. Each polymerase II factory contains ~8 polymerases. As most active transcription units are associated with only one polymerase, each factory usually contains ~8 different transcription units. These units might be associated through promoters and/or enhancers, with loops forming a "cloud" around the factor.[20]
History[edit]
A molecule that allows the genetic material to be realized as a protein was first hypothesized by François Jacob and Jacques Monod. Severo Ochoa won a Nobel Prize in Physiology or Medicine in 1959 for developing a process for synthesizing RNA in vitro with polynucleotide phosphorylase, which was useful for cracking the genetic code. RNA synthesis by RNA polymerase was established in vitro by several laboratories by 1965; however, the RNA synthesized by these enzymes had properties that suggested the existence of an additional factor needed to terminate transcription correctly.[citation needed]
In 1972, Walter Fiers became the first person to actually prove the existence of the terminating enzyme.
Roger D. Kornberg won the 2006 Nobel Prize in Chemistry "for his studies of the molecular basis of eukaryotic transcription".[21]
Measuring and detecting[edit]
Electron micrograph of transcription of ribosomal RNA. The forming ribosomal RNA strands are visible as branches from the main DNA strand.[citation needed]
Transcription can be measured and detected in a variety of ways:[citation needed]
G-Less Cassette transcription assay: measures promoter strength
Run-off transcription assay: identifies transcription start sites (TSS)
Nuclear run-on assay: measures the relative abundance of newly formed transcripts
RNase protection assay and ChIP-Chip of RNAP: detect active transcription sites
RT-PCR: measures the absolute abundance of total or nuclear RNA levels, which may however differ from transcription rates
DNA microarrays: measures the relative abundance of the global total or nuclear RNA levels; however, these may differ from transcription rates
In situ hybridization: detects the presence of a transcript
MS2 tagging: by incorporating RNA stem loops, such as MS2, into a gene, these become incorporated into newly synthesized RNA. The stem loops can then be detected using a fusion of GFP and the MS2 coat protein, which has a high affinity, sequence-specific interaction with the MS2 stem loops. The recruitment of GFP to the site of transcription is visualized as a single fluorescent spot. This new approach has revealed that transcription occurs in discontinuous bursts, or pulses (see Transcriptional bursting). With the notable exception of in situ techniques, most other methods provide cell population averages, and are not capable of detecting this fundamental property of genes.[22]
Northern blot: the traditional method, and until the advent of RNA-Seq, the most quantitative
RNA-Seq: applies next-generation sequencing techniques to sequence whole transcriptomes, which allows the measurement of relative abundance of RNA, as well as the detection of additional variations such as fusion genes, post-transcriptional edits and novel splice sites
Reverse transcription[edit]
Scheme of reverse transcription
Main article: Reverse transcription
Some viruses (such as HIV, the cause of AIDS), have the ability to transcribe RNA into DNA. HIV has an RNA genome that is reverse transcribed into DNA. The resulting DNA can be merged with the DNA genome of the host cell. The main enzyme responsible for synthesis of DNA from an RNA template is called reverse transcriptase.
In the case of HIV, reverse transcriptase is responsible for synthesizing a complementary DNA strand (cDNA) to the viral RNA genome. The enzyme ribonuclease H then digests the RNA strand, and reverse transcriptase synthesises a complementary strand of DNA to form a double helix DNA structure ("cDNA"). The cDNA is integrated into the host cell's genome by the enzyme integrase, which causes the host cell to generate viral proteins that reassemble into new viral particles. In HIV, subsequent to this, the host cell undergoes programmed cell death, or apoptosis of T cells.[23] However, in other retroviruses, the host cell remains intact as the virus buds out of the cell.
Some eukaryotic cells contain an enzyme with reverse transcription activity called telomerase. Telomerase is a reverse transcriptase that lengthens the ends of linear chromosomes. Telomerase carries an RNA template from which it synthesizes a repeating sequence of DNA, or "junk" DNA. This repeated sequence of DNA is called a telomere and can be thought of as a "cap" for a chromosome. It is important because every time a linear chromosome is duplicated, it is shortened. With this "junk" DNA or "cap" at the ends of chromosomes, the shortening eliminates some of the non-essential, repeated sequence rather than the protein-encoding DNA sequence, that is farther away from the chromosome end.
Telomerase is often activated in cancer cells to enable cancer cells to duplicate their genomes indefinitely without losing important protein-coding DNA sequence. Activation of telomerase could be part of the process that allows cancer cells to become immortal. The immortalizing factor of cancer via telomere lengthening due to telomerase has been proven to occur in 90% of all carcinogenic tumors in vivo with the remaining 10% using an alternative telomere maintenance route called ALT or Alternative Lengthening of Telomeres.[24]
See also[edit]
Crick's central dogma, in which the product of transcription, mRNA, is translated to form polypeptides, and where it is asserted that the reverse processes never occur
Gene regulation
Splicing - process of removing introns from precursor messenger RNA (pre-mRNA) to make messenger RNA (mRNA)
Transcriptomics
References[edit]
^ Jump up to: a b c Eldra P. Solomon, Linda R. Berg, Diana W. Martin. Biology, 8th Edition, International Student Edition. Thomson Brooks/Cole. ISBN 978-0495317142
Jump up ^ Koonin EV, Gorbalenya AE, Chumakov KM (July 1989). "Tentative identification of RNA-dependent RNA polymerases of dsRNA viruses and their relationship to positive strand RNA viral polymerases". FEBS Letters. 252 (1-2): 42–6. doi:10.1016/0014-5793(89)80886-5. PMID 2759231.
Jump up ^ http://www.sci.sdsu.edu/~smaloy/MicrobialGenetics/topics/chroms-genes-prots/temp-strand.html
Jump up ^ Berg J, Tymoczko JL, Stryer L (2006). Biochemistry (6th ed.). San Francisco: W. H. Freeman. ISBN 0-7167-8724-5.
^ Jump up to: a b c d e f g Watson JD, Baker TA, Bell SP, Gann AA, Levine M, Losick RM (2013). Molecular Biology of the Gene (7th ed.). Pearson.
Jump up ^ Roeder, Robert G. (1991). "The complexities of eukaryotic transcription initiation: regulation of preinitiation complex assembly". Trends in Biochemical Sciences. 16: 402–408. doi:10.1016/0968-0004(91)90164-Q. ISSN 0968-0004.
Jump up ^ Goldman SR, Ebright RH, Nickels BE (May 2009). "Direct detection of abortive RNA transcripts in vivo". Science. 324 (5929): 927–8. doi:10.1126/science.1169237. PMC 2718712  . PMID 19443781.
Jump up ^ Revyakin A, Liu C, Ebright RH, Strick TR (November 2006). "Abortive initiation and productive initiation by RNA polymerase involve DNA scrunching". Science. 314 (5802): 1139–43. doi:10.1126/science.1131398. PMC 2754787  . PMID 17110577.
Jump up ^ Raffaelle M, Kanin EI, Vogt J, Burgess RR, Ansari AZ (November 2005). "Holoenzyme switching and stochastic release of sigma factors from RNA polymerase in vivo". Molecular Cell. 20 (3): 357–66. doi:10.1016/j.molcel.2005.10.011. PMID 16285918.
Jump up ^ Mandal SS, Chu C, Wada T, Handa H, Shatkin AJ, Reinberg D (May 2004). "Functional interactions of RNA-capping enzyme with factors that positively and negatively regulate promoter escape by RNA polymerase II". Proceedings of the National Academy of Sciences of the United States of America. 101 (20): 7572–7. doi:10.1073/pnas.0401493101. PMC 419647  . PMID 15136722.
Jump up ^ Goodrich JA, Tjian R (April 1994). "Transcription factors IIE and IIH and ATP hydrolysis direct promoter clearance by RNA polymerase II". Cell. 77 (1): 145–56. doi:10.1016/0092-8674(94)90242-9. PMID 8156590.
Jump up ^ Milo, Ron; Philips, Rob. "Cell Biology by the Numbers: What is faster, transcription or translation?". book.bionumbers.org. Retrieved 8 March 2017.
Jump up ^ Richardson JP (September 2002). "Rho-dependent termination and ATPases in transcript termination". Biochimica et Biophysica Acta. 1577 (2): 251–260. doi:10.1016/S0167-4781(02)00456-6. PMID 12213656.
Jump up ^ Lykke-Andersen S, Jensen TH (October 2007). "Overlapping pathways dictate termination of RNA polymerase II transcription". Biochimie. 89 (10): 1177–82. doi:10.1016/j.biochi.2007.05.007. PMID 17629387.
Jump up ^ 8-Hydroxyquinoline info from SIGMA-ALDRICH. Retrieved Feb 2012
Jump up ^ Saxonov S, Berg P, Brutlag DL (January 2006). "A genome-wide analysis of CpG dinucleotides in the human genome distinguishes two distinct classes of promoters". Proceedings of the National Academy of Sciences of the United States of America. 103 (5): 1412–7. doi:10.1073/pnas.0510310103. PMC 1345710  . PMID 16432200.
Jump up ^ Bird A (January 2002). "DNA methylation patterns and epigenetic memory". Genes & Development. 16 (1): 6–21. doi:10.1101/gad.947102. PMID 11782440.
Jump up ^ Vogelstein B, Papadopoulos N, Velculescu VE, Zhou S, Diaz LA, Kinzler KW (March 2013). "Cancer genome landscapes". Science. 339 (6127): 1546–58. doi:10.1126/science.1235122. PMC 3749880  . PMID 23539594.
Jump up ^ Tessitore A, Cicciarelli G, Del Vecchio F, Gaggiano A, Verzella D, Fischietti M, Vecchiotti D, Capece D, Zazzeroni F, Alesse E (2014). "MicroRNAs in the DNA Damage/Repair Network and Cancer". International Journal of Genomics. 2014: 820248. doi:10.1155/2014/820248. PMC 3926391  . PMID 24616890.
Jump up ^ Papantonis, A (2012-10-26). "TNFα signals through specialized factories where responsive coding and miRNA genes are transcribed". EMBO J. CiteSeerX 10.1.1.919.1919  . doi:10.1038/emboj.2012.288. PMC 3512387  . PMID 23103767.
Jump up ^ "Chemistry 2006". Nobel Foundation. Retrieved March 29, 2007.
Jump up ^ Raj A, van Oudenaarden A (October 2008). "Nature, nurture, or chance: stochastic gene expression and its consequences". Cell. 135 (2): 216–26. doi:10.1016/j.cell.2008.09.050. PMC 3118044  . PMID 18957198.
Jump up ^ Kolesnikova IN (2000). "Some patterns of apoptosis mechanism during HIV-infection". Dissertation (in Russian). Retrieved February 20, 2011.
Jump up ^ Cesare AJ, Reddel RR (2010). "Alternative lengthening of telomeres: models, mechanisms and implications". Nature Reviews. Genetics. 11 (5): 319–30. doi:10.1038/nrg2763. PMID 20351727.
External links[edit]
Wikimedia Commons has media related to Transcription (genetics).
Wikiversity has learning resources about Transcription (biology)
Interactive Java simulation of transcription initiation. From Center for Models of Life at the Niels Bohr Institute.
Interactive Java simulation of transcription interference--a game of promoter dominance in bacterial virus. From Center for Models of Life at the Niels Bohr Institute.
Biology animations about this topic under Chapter 15 and Chapter 18
Virtual Cell Animation Collection, Introducing Transcription
Easy to use DNA transcription site
[show]
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Gene expression
Introduction
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DNA → RNA → Protein
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Transcription
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Transcription factor
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bacterial RNA polymerase: rpoB
eukaryotic RNA polymerase: RNA polymerase II
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(bacterial,
eukaryotic)
Terminator
Intrinsic termination
Rho factor
Authority control
GND: 4185906-6
NDL: 00857944
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Old Major
From Wikipedia, the free encyclopedia
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Old Major
First appearance
Animal Farm
Last appearance
Animal Farm (Only Appearance)
Created by
George Orwell
Voiced by
Maurice Denham (1954 film)
Peter Ustinov (1999 film)
Information
Nickname(s)
Willingdon Beauty
Species
Middle White boar
Gender
Male
Occupation
Revolutionary Leader of Animal Farm
Old Major (also called Willingdon Beauty, his name used when showing) is the first major character described by George Orwell in Animal Farm. This "purebred" of pigs is a kind, grandfatherly philosopher of change.
Old Major proposes a solution to the animals' desperate plight on Manor Farm under the Jones administration and inspires thoughts of a rebellion. The actual time of the revolt is unsaid; it could be tomorrow or several generations down the road. Old Major dies three days after delivering his speech and the animals, stirred up by this speech, set to work immediately on the bringing about of the Rebellion.
Shortly after his death, the animals rise in revolt and oust the humans from power. This rebellious act is so quick that many do not realize it has happened until it is over. The animals drive Jones and the farmhands off the farm and remove many of the implements of his rule.
The Seven Commandments that Snowball transcribes, that are supposed to encompass Old Major's general philosophy, are gradually altered and deformed under Napoleon until they have entirely different meanings from those originally intended. "Beasts of England", the song that came to Old Major in his dream, is later banned on Animal Farm by Napoleon, at which time it is replaced by "Comrade Napoleon", a hymn composed by Minimus the pig that pledges allegiance to Animal Farm and to work to protect it.
In both film adaptations, Major dies while provoking the animals into rebelling. In the 1954 adaption (voiced by Maurice Denham), he dies suddenly while the animals are singing. In the 1999 version (voiced by Peter Ustinov), Farmer Jones slips in mud while investigating the sounds coming from the barn, which sets off his shotgun, and indirectly hits Major in his backside, killing him.
Major's skull is dug up and saluted by the animals every day, even after the rebellion, as a sign of respect that the animals remember their roots and the roots of the Rebellion. Napoleon, who later decides to accept the humans and strike bargains with them, announces that the remains are to be disposed of because they represent the old days when Animal Farm was "violent and primitive" towards humans; towards the end of the story, Napoleon announces that he has reburied the skull.
References[edit]
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Old Major
Napoleon
Snowball
Squealer
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Pilkington
Mr. Jones
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1954 film
1999 film
This article about a fictional character from a novel is a stub. You can help Wikipedia by expanding it.
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Retrieved from "https://en.wikipedia.org/w/index.php?title=Old_Major&oldid=830395546"
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List of Maharashtra Government Engineering Colleges
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List of Government of Maharashtra's Engineering Colleges
No.
College Name
Location
Type
Autonomy Status
Affiliation
Estd
Weblink
1. College of Engineering, Pune Pune Government Autonomous Savitribai Phule Pune University 1854 coep.org.in
2. Government College of Engineering, Aurangabad Aurangabad Government Autonomous Dr. Babasaheb Ambedkar Marathwada University 1960 geca.ac.in
3. Government College of Engineering, Karad Karad Government Autonomous Shivaji University 1960 gcekarad.ac.in
4. Government College of Engineering, Amravati Amravati Government Autonomous Sant Gadge Baba Amravati University 1964 gcoea.ac.in
5. Government College of Engineering, Jalgaon Jalgaon Government Autonomous North Maharashtra University 1996 gcoej.ac.in
6. Government College of Engineering, Chandrapur Chandrapur Government Non-Autonomous Gondwana University 1996 gcoec.ac.in
7. Government College of Engineering and Research, Avasari Avasari (Khurd), Dist-Pune Government Non-Autonomous Savitribai Phule Pune University 2009 gcoeara.ac.in
8. Government College of Engineering, Nagpur Nagpur Government Non-Autonomous Rashtrasant Tukadoji Maharaj Nagpur University 2016 gcoen.ac.in
List of Government of Maharashtra's-Aided Engineering Colleges
No.
College Name
Location
Type
Autonomy Status
Affiliation
Estd
nk
1. Veermata Jijabai Technological Institute Mumbai Government-Aided Autonomous University of Mumbai 1887 vjti.ac.in
2. Walchand College of Engineering Sangli Government-Aided Autonomous Shivaji University, Kolhapur 1947 walchandsangli.ac.in
3. Shri Guru Gobind Singhji Institute of Engineering and Technology Nanded Government-Aided Autonomous Swami Ramanand Teerth Marathwada University 1981 sggs.ac.in
4. Sardar Patel College of Engineering Mumbai Government-Aided Autonomous University of Mumbai 1995 www.spce.ac.in
List of University Department Institutes
No.
College Name
Location
Type
Autonomy Status
Affiliation/University Department of
Estd
Weblink
1. Laxminarayan Institute of Technology Nagpur State University Department Non-Autonomous Rashtrasant Tukadoji Maharaj Nagpur University 1942 litnagpur.in
2. University Department of Sant Gadge Baba Amravati University Amravati State University Department Non-Autonomous Sant Gadge Baba Amravati University 1993 sgbau.ac.in
3. University Institute of Chemical Technology, North Maharashtra University Jalgaon State University Department Non-Autonomous North Maharashtra University 1994 nmu.ac.in/udct/
4 University Department of Chemical Technology, Aurangabad Aurangabad State University Department Non-Autonomous Dr. Babasaheb Ambedkar Marathwada University 1998 bamu.ac.in
5. Department of Technology, Shivaji University, Kolhapur Kolhapur State University Department Non-Autonomous Shivaji University, Kolhapur 2006 apps.unishivaji.ac.in
List of University Managed Institutes
No.
College Name
Location
Type
Autonomy Status
Affiliation/Managed by University
Estd
Weblink
1. Dr. Babasaheb Ambedkar Technological University Lonere, Dist-Raigad State University Managed Non-Autonomous Dr. Babasaheb Ambedkar Technological University 1989 dbatu.ac.in
2. Usha Mittal Institute of Technology Mumbai State University Managed (Un-Aided) Non-Autonomous SNDT Women's University 1997 umit.ac.in
Deemed University (Maharashtra Government funded)
University Name
Location
Type
Autonomy Status
Estd
Weblink
Institute of Chemical Technology Mumbai State funded - Deemed University Autonomous 1933 ictmumbai.edu.in
See also[edit]
List of Government Polytechnic colleges in Maharashtra
List of Kerala Government Engineering Colleges
List of Rajasthan Government Engineering Colleges
List of Tamil Nadu Government Engineering Colleges
Retrieved from "https://en.wikipedia.org/w/index.php?title=List_of_Maharashtra_Government_Engineering_Colleges&oldid=852899855"
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Indian State Government Engineering Colleges
Lists of universities and colleges in Maharashtra
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