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You don't have to be a student to be a part of the college. Journal of cell biology. Posted by Shakingfist March 28, 6: Both of these amino acids are found in peptidic lantibiotics such as alamethicin. Here are the benefits: You're literally complaining that an otherwise sound article is not politically correct enough for your friends and that it is Alone who should adjust, not your friends. Accounting theory and practice related to the acquisition, use and disposal of fixed and intangible assets.
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But at pH between 2. This molecular state is known as a zwitterion , from the German Zwitter meaning hermaphrodite or hybrid. Amino acids exist as zwitterions also in the solid phase, and crystallize with salt-like properties unlike typical organic acids or amines. The variation in titration curves when the amino acids can be grouped by category. At pH values between the two pKa values, the zwitterion predominates, but coexists in dynamic equilibrium with small amounts of net negative and net positive ions.
At the exact midpoint between the two pKa values, the trace amount of net negative and trace of net positive ions exactly balance, so that average net charge of all forms present is zero. The individual amino acids all have slightly different pKa values, so have different isoelectric points.
For amino acids with charged side chains, the pKa of the side chain is involved. Amino acids have zero mobility in electrophoresis at their isoelectric point, although this behaviour is more usually exploited for peptides and proteins than single amino acids.
Zwitterions have minimum solubility at their isoelectric point and some amino acids in particular, with non-polar side chains can be isolated by precipitation from water by adjusting the pH to the required isoelectric point. Amino acids are the structural units monomers that make up proteins.
They join together to form short polymer chains called peptides or longer chains called either polypeptides or proteins. These polymers are linear and unbranched, with each amino acid within the chain attached to two neighboring amino acids. Twenty-two amino acids are naturally incorporated into polypeptides and are called proteinogenic or natural amino acids.
The remaining 2, selenocysteine and pyrrolysine , are incorporated into proteins by unique synthetic mechanisms. It is coded for with the codon UAG, which is normally a stop codon in other organisms. Aside from the 22 proteinogenic amino acids , many non-proteinogenic amino acids are known.
Those either are not found in proteins for example carnitine , GABA , levothyroxine or are not produced directly and in isolation by standard cellular machinery for example, hydroxyproline and selenomethionine. Non-proteinogenic amino acids that are found in proteins are formed by post-translational modification , which is modification after translation during protein synthesis. These modifications are often essential for the function or regulation of a protein.
For example, the carboxylation of glutamate allows for better binding of calcium cations ,  and collagen contains hydroxyproline, generated by hydroxylation of proline.
Some non-proteinogenic amino acids are not found in proteins. Examples include 2-aminoisobutyric acid and the neurotransmitter gamma-aminobutyric acid. D -isomers are uncommon in live organisms. For instance, gramicidin is a polypeptide made up from mixture of D - and L -amino acids. These compounds disrupt bacterial cell walls, particularly in Gram-positive bacteria. Only D -amino acids were found in Swiss-Prot database million amino acids analysed.
The 20 amino acids that are encoded directly by the codons of the universal genetic code are called standard or canonical amino acids. A modified form of methionine N -formylmethionine is often incorporated in place of methionine as the initial amino acid of proteins in bacteria, mitochondria and chloroplasts. Other amino acids are called non-standard or non-canonical. Most of the non-standard amino acids are also non-proteinogenic i.
The two non-standard proteinogenic amino acids are selenocysteine present in many non-eukaryotes as well as most eukaryotes, but not coded directly by DNA and pyrrolysine found only in some archaea and one bacterium. The incorporation of these non-standard amino acids is rare. For example, 25 human proteins include selenocysteine Sec in their primary structure,  and the structurally characterized enzymes selenoenzymes employ Sec as the catalytic moiety in their active sites.
When taken up into the human body from the diet, the 20 standard amino acids either are used to synthesize proteins and other biomolecules or are oxidized to urea and carbon dioxide as a source of energy. The other product of transamidation is a keto acid that enters the citric acid cycle. In humans, non-protein amino acids also have important roles as metabolic intermediates , such as in the biosynthesis of the neurotransmitter gamma-amino-butyric acid GABA.
Many amino acids are used to synthesize other molecules, for example:. Some non-standard amino acids are used as defenses against herbivores in plants. Amino acids are used for a variety of applications in industry, but their main use is as additives to animal feed. This is necessary, since many of the bulk components of these feeds, such as soybeans , either have low levels or lack some of the essential amino acids: The food industry is also a major consumer of amino acids, in particular, glutamic acid , which is used as a flavor enhancer ,  and aspartame aspartyl-phenylalaninemethyl ester as a low-calorie artificial sweetener.
The chelating ability of amino acids has been used in fertilizers for agriculture to facilitate the delivery of minerals to plants in order to correct mineral deficiencies, such as iron chlorosis.
These fertilizers are also used to prevent deficiencies from occurring and improving the overall health of the plants. Similarly, some amino acids derivatives are used in pharmaceutical industry. They include 5-HTP 5-hydroxytryptophan used for experimental treatment of depression,  L -DOPA L -dihydroxyphenylalanine for Parkinson's treatment,  and eflornithine drug that inhibits ornithine decarboxylase and used in the treatment of sleeping sickness.
Since , 40 non-natural amino acids have been added into protein by creating a unique codon recoding and a corresponding transfer-RNA: Nullomers are codons that in theory code for an amino acid, however in nature there is a selective bias against using this codon in favor of another, for example bacteria prefer to use CGA instead of AGA to code for arginine. This characteristic can be taken advantage of and used to create new selective cancer-fighting drugs  and to prevent cross-contamination of DNA samples from crime-scene investigations.
Amino acids are important as low-cost feedstocks. These compounds are used in chiral pool synthesis as enantiomerically pure building-blocks. Amino acids have been investigated as precursors chiral catalysts , e. Amino acids are under development as components of a range of biodegradable polymers.
These materials have applications as environmentally friendly packaging and in medicine in drug delivery and the construction of prosthetic implants. These polymers include polypeptides, polyamides , polyesters, polysulfides, and polyurethanes with amino acids either forming part of their main chains or bonded as side chains. These modifications alter the physical properties and reactivities of the polymers. As amino acids have both a primary amine group and a primary carboxyl group, these chemicals can undergo most of the reactions associated with these functional groups.
These include nucleophilic addition , amide bond formation, and imine formation for the amine group, and esterification , amide bond formation, and decarboxylation for the carboxylic acid group. Several methods exist to synthesize amino acids. Nucleophilic substitution with ammonia then converts the alkyl bromide to the amino acid.
At the current time, the most-adopted method is an automated synthesis on a solid support e. As both the amine and carboxylic acid groups of amino acids can react to form amide bonds, one amino acid molecule can react with another and become joined through an amide linkage. This polymerization of amino acids is what creates proteins.
This condensation reaction yields the newly formed peptide bond and a molecule of water. In cells, this reaction does not occur directly; instead, the amino acid is first activated by attachment to a transfer RNA molecule through an ester bond. However, not all peptide bonds are formed in this way. In a few cases, peptides are synthesized by specific enzymes. For example, the tripeptide glutathione is an essential part of the defenses of cells against oxidative stress.
This peptide is synthesized in two steps from free amino acids. This dipeptide is then condensed with glycine by glutathione synthetase to form glutathione. In chemistry, peptides are synthesized by a variety of reactions. One of the most-used in solid-phase peptide synthesis uses the aromatic oxime derivatives of amino acids as activated units. These are added in sequence onto the growing peptide chain, which is attached to a solid resin support.
In plants, nitrogen is first assimilated into organic compounds in the form of glutamate , formed from alpha-ketoglutarate and ammonia in the mitochondrion. In order to form other amino acids, the plant uses transaminases to move the amino group to another alpha-keto carboxylic acid.
For example, aspartate aminotransferase converts glutamate and oxaloacetate to alpha-ketoglutarate and aspartate. Nonstandard amino acids are usually formed through modifications to standard amino acids.
For example, homocysteine is formed through the transsulfuration pathway or by the demethylation of methionine via the intermediate metabolite S-adenosyl methionine ,  while hydroxyproline is made by a posttranslational modification of proline.
Microorganisms and plants can synthesize many uncommon amino acids. For example, some microbes make 2-aminoisobutyric acid and lanthionine , which is a sulfide-bridged derivative of alanine. Both of these amino acids are found in peptidic lantibiotics such as alamethicin. Amino acids must first pass out of organelles and cells into blood circulation via amino acid transporters , since the amine and carboxylic acid groups are typically ionized.
Degradation of an amino acid, occurring in the liver and kidneys, often involves deamination by moving its amino group to alpha-ketoglutarate, forming glutamate. This process involves transaminases, often the same as those used in amination during synthesis. In many vertebrates, the amino group is then removed through the urea cycle and is excreted in the form of urea.
In Egypt, development of rooftop gardens began in the s. In the early s at Ain Shams University , a group of agriculture professors developed an initiative focused on growing organic vegetables to suit densely populated cities of Egypt. The initiative was applied on a small scale; until it was officially adopted in , by the Food and Agriculture Organization FAO.
After the disintegration of the Soviet Union and the Eastern Bloc , Cuba faced severe shortages of fuel and agrochemical inputs. These products had previously been imported from the Soviet Union in exchange for Cuban sugar. As a result, Cubans experienced an acute food crisis in the early s, which in part was met with a popular movement of urban agriculture.
Urban farmers employed — and still employ — agroecological techniques, allowing food production to take place largely without petroleum-based inputs. In , more than , Cubans worked in the expanding urban agriculture sector.
Economic development in Mumbai brought a growth in population caused mainly by the migration of laborers from other regions of the country. The number of residents in the city increased more than twelve times in the last century. In this scenario, urban agriculture seems unlikely to be put into practice since it must compete with real estate developers for the access and use of vacant lots.
Alternative farming methods have emerged as a response to the scarcity of land, water, and economic resources employed in UPA. Doshi's city garden methods are revolutionary for being appropriate to apply in reduced spaces as terraces and balconies, even on civil construction walls, and for not requiring big investments in capital or long hours of work.
His farming practice is purely organic and is mainly directed to domestic consumption. His gardening tools are composed of materials available in the local environment: The containers and bags open at both ends are filled with the sugarcane stalks, compost, and garden soil, which make possible the use of a minimal quantity of water is compared to open fields.
Doshi states that solar energy can replace soil in cities. He also recommends the idea of chain planning, or growing plants in intervals and in small quantities rather than at once and in large amounts.
The concept of city farming developed by Dr. Doshi consumes the entire household's organic waste. He subsequently makes the household self-sufficient in the provision of food: The main objectives of a pilot project at city farm at Rosary High School, Dockyard Road, were to promote economic support for street children, beautify the city landscape, supply locally produced organic food to urban dwellers mainly those residing in slums , and to manage organic waste in a sustainable city.
The project was conducted in the Rosary School, in Mumbai, with the participation of street children during The participants were trained in urban farming techniques. The farm produced vegetables, fruits, and flowers. The idea has spread the concept of city farm to other schools in the city.
The Mumbai Port Trust MBPT central kitchen distributes food to approximately 3, employees daily, generating important amounts of organic disposal. A terrace garden created by the staff recycles ninety percent of this waste in the production of vegetables and fruits.
The activity of city farming was started initially to dispose of kitchen organic waste in an eco-friendly way. Staff members, after their daily work in the kitchen, tend the garden, which has about plants. While the goals of the NGO are important in a global context, the community goals are being met through the work of forming the urban gardens themselves.
In this sense, the creation, implementation, and maintenance of urban gardens are highly determined by the desires of the communities involved. However, the criteria by which TEI measured their success illustrates the scope of benefits to a community which practices urban agriculture.
TEI's success indicators were:. Recently, with relative food security in China, periurban agriculture has led to improvements in the quality of the food available, as opposed to quantity. One of the more recent experiments in urban agriculture is the Modern Agricultural Science Demonstration Park in Xiaotangshan. Traditionally, Chinese cities have been known to mix agricultural activities within the urban setting.
Shenzhen, once a small farming community, is now a fast-growing metropolis due to the Chinese government designation as an open economic zone. Due to large and growing population in China, the government supports urban self-sufficiency in food production. Shenzhen's village structure, sustainable methods, and new agricultural advancements initiated by the government have been strategically configured to supply food for this growing city. The city farms are located about 10 kilometres 6.
The first tier approached from city center produces perishable items. Located just outside these farms, hardier vegetables are grown such as potatoes, carrots, and onions. This system allows producers to be sold in city markets just a few short hours after picking. Another impressive method used in Chinese agriculture and aquaculture practice is the mulberry-dike fish-pond system, which is a response to waste recycling and soil fertility.
This system can be described as: Mulberry trees are grown to feed silkworms and the silkworm waste is fed to the fish in ponds. The fish also feed on waste from other animals, such as pigs, poultry, and buffalo. The animals, in turn, are given crops that have been fertilized by mud from the ponds. This is a sophisticated system as a continuous cycle of water, waste, and food As the population grows and industry advances, the city tries to incorporate potential agricultural growth by experimenting with new agricultural methods.
This farm was established with aspirations of producing large quantities and high-quality lychees, by constantly monitoring sugar content, and their seeds. This research, conducted by local agricultural universities allows for new methods to be used with hopes of reaching the needs of city consumers.
However, due to increased levels of economic growth and pollution, some urban farms have become threatened. The government has been trying to step in and create new technological advancements within the agricultural field to sustain levels of urban agriculture. According to the Municipal Bureau of Agriculture, Forestry and Fishery the city will invest million yuan on farms located around the city, with hopes of the farms to provide "60 percent of the meat, vegetables, and aquatic products in the Shenzhen market".
There has also been an emerging trend of going green and organic as a response to pollution and pesticides used in farming practices. Vegetable suppliers are required to pass certain inspections held by the city's Agriculture Bureau before they can be sold as "green". Harare is particularly suited for urban agriculture, as its topography heavily features vleis , land drainage systems that become waterlogged in the rainy season.
When it rains they are difficult to cross, and in the dry season they shrink and crack, which causes structural damage to infrastructure, even though the vleis are still storing water underground.
Therefore, these moisture-rich areas are mostly left unbuilt, allowing for urban cultivation. Aside from vleis and the private residential land that Harareans cultivate, considerable public land is used for agriculture in Harare: However, urban agriculture in Harare causes harm to the environment. The practice has reduced rainwater infiltration into the soil by In the s, the failure of Structural Adjustment Programs induced greater unemployment, higher prices, and lower incomes, so more people started growing their own food.
The practice continued in the s when a major recession brought about widespread poverty, unemployment, and enormous inflation. Finally, the Nyanga Declaration on Urban Agriculture in Zimbabwe explicitly acknowledged the value of urban agriculture for food security and the reduction of poverty. Accepting that many people depend on it to survive, the government allocated sixty thousand hectares of land in Harare for cultivation purposes.
In New York City , many low-income residents suffer from high rates of obesity and diabetes and limited sources of fresh produce. The City and local nonprofit groups have been providing land, training and financial encouragement, but the impetus in urban farming has really come from the farmers, who often volunteer when their regular work day is done.
Eligible projects include green roofs, rooftop farms, and rainwater harvesting on private property in combined sewer areas. Because of this grant program, New York City now has the world's largest rooftop farms. Some urban gardeners have used empty lots to start a community or urban gardens.
However, the soil must be tested for heavy contamination in city soil because of vehicle exhaust and remnants of old construction. The City also has a composting program, which is available to gardeners and farmers. One group, GreenThumb, provides free seedlings. Another program, the City Farms project operated by the nonprofit Just Food, offers courses on growing and selling food. Two alternate means of growing are rooftop gardens and hydroponic soil-less growing.
The New York Times wrote an article about one of Manhattan's first gardens which incorporate both these techniques. In response to the recession of , a coalition of community-based organizations, farmers, and academic institutions in California's Pomona Valley formed the Pomona Valley Urban Agriculture Initiative. After the passage of the North American Free Trade Agreement , cheap grain from the United States flooded Mexico, driving peasant farmers off of their land.
Many immigrated to the Pomona Valley and found work in the construction industry. With the recession, the construction industry also suffered in the region. It is unlikely to regain its former strength because of severe water shortages in this desert region as well as ongoing weakness in the local economy.
These immigrants were dry land organic farmers in their home country by default since they did not have access to pesticides and petroleum-based fertilizers. Now, they found themselves on the border of two counties: Los Angeles County with a population of 10 million and almost no farmland, and San Bernardino County which has the worst access to healthy food in the state.
In response to these conditions, Uncommon Good, a community-based nonprofit organization that works with immigrant farmer families, convened a forum which became the Urban Farmers Association. The Urban Farmers Association is the first organization of its kind for poor immigrant farmers in the Pomona Valley.
Its goal is to develop opportunities for its members to support themselves and their families through urban agriculture. Urban agriculture in West Oakland has taken a radical form that can be traced back to community gardening initiatives starting in the s in the cities of Berkeley and Oakland , and the city's African-American heritage.
To reduce racial tension, the Oakland Housing Authority established housing projects for blacks in West Oakland and whites in East Oakland.
With exclusionary covenants and redlining by banks, development capital was kept out of West Oakland while the African-American population had limited opportunities to rent or buy housing outside West Oakland.
A small amount of this food came from small local gardens planted by BPP members. Nathan McClintock, "The Panthers used gardening as a coping mechanism and a means of supplementing their diets, as a well as a means to strengthen community members engaged in the struggle against oppression.
The group planted in empty and vacant lots in West Oakland. In addition, schools around Alameda County began teaching basic gardening skills and food education. City Slicker Farms was founded in in response to the lack of access to fresh produce in West Oakland. Through land donations from local residents, a network of urban farms was created through the Community Market Farms Program, and in the organization established the Backyard Garden Program to aid West Oakland residents in growing their own food at home.
A study conducted on urban farms in surveyed over farms that identified as urban. The survey found that most urban farms in the United States are structured as either non-profit or solely owned. Urban farms typically use techniques that allow them to produce intensively on small land.
Mainly, these practices include raised beds, greenhouse, and container gardens. Of the products made, an overwhelming majority of urban farms focus on fresh vegetable, followed by herbs and flowers. If an urban farm focuses on animals, the primary animal is hens. Bees and sheep are the second most common urban farm animals. Most urban farms agree on the main challenges that they face; production costs, managing pests, managing weeds, and climate.
They also see profitability, financing, and farm labor as big challenges of managing an urban farm. Canada has a number of companies working on urban farm technology, including Lufa Farms. In Montreal, there are 97 community gardens which allow citizens space in each plot to grow their plants. The program has been in place since and is managed by the boroughs. Of the eighteen boroughs, some have a gardening instructor who visits the gardens regularly to give gardeners tips.
The soil, a water supply, a space for tools, sand, fencing, and paint are all provided by the city. A Canadian urban farmer in British Columbia has published details on a crop value rating CVR system that urban farmers can use to determine which crops to grow, based on each crop's contribution to supporting the farm economically.
For example, the urban farmer may not be able to economically justify growing sweet corn based on long days to maturity and low yield density per linear foot of row , but a networking arrangement is mutually beneficial, as it lets a rural sweet corn grower gain an additional point of sale at retail price while also letting the urban farmer fill the gap in his product line offering.
Todmorden is a town of 17, inhabitants in Yorkshire , United Kingdom with a successful urban agriculture model. The project, which began in , has meant that food crops have been planted at forty locations throughout the town. All are "propaganda gardens" promoting locals to consider growing local, to eat seasonal, to consider the provenance of their food, and to enjoy fresh.
The city of Rosario population: Its Land Use Plan makes specific provision for the agricultural use of public land. In , the green circuit consisted of more than 30 ha of land used to grow vegetables, fruit and medicinal and aromatic plants. The city has five garden parks — large, landscaped green areas covering a total of 72 ha of land, which are used for agriculture and for cultural, sports and educational activities.
The benefits that UPA brings along to cities that implement this practice are numerous. The transformation of cities from only consumers of food to generators of agricultural products contributes to sustainability, improved health, and poverty alleviation. It is known that a large part of the people involved in urban agriculture is the urban poor. In developing countries, the majority of urban agricultural production is for self-consumption, with surpluses being sold in the market.
According to the FAO Food and Agriculture Organization of the United Nations , urban poor consumers spend between 60 and 80 percent of their income on food, making them very vulnerable to higher food prices.