Monthly Archives: February 2012

Amino Acids

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Amino Acids are an important class of organic compounds that contain both the amino (8NH2) and carboxyl (8COOH) groups. Of these acids, 20 serve as the building blocks of proteins. Known as the standard, or alpha, amino acids, they include alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. All 20 are constructed according to a general formula:

As the formula shows, the amino and carboxyl groups are both attached to a single carbon atom, which is called the alpha carbon atom. Attached to the carbon atom is a variable group (R); it is in their R groups that the molecules of the 20 standard amino acids differ from one another. In the simplest of the acids, glycine, the R consists of a single hydrogen atom. Other amino acids have more complex R groups that contain carbon as well as hydrogen and may include oxygen, nitrogen, or sulfur, as well.

When a living cell makes protein, the carboxyl group of one amino acid is linked to the amino group of another to form a peptide bond. The carboxyl group of the second amino acid is similarly linked to the amino group of a third, and so on, until a long chain is produced. This chainlike molecule, which may contain from 50 to several hundred amino acid subunits, is called a polypeptide. A protein may be formed of a single polypeptide chain, or it may consist of several such chains held together by weak molecular bonds. Each protein is formed according to a precise set of instructions contained within the nucleic acid (see Nucleic Acids), which is the genetic material of the cell. These instructions decide which of the 20 standard amino acids are to be incorporated into the protein, and in what sequence. The R groups of the amino acid subunits determine the final shape of the protein and its chemical properties; an extraordinary variety of proteins can be produced from the same 20 subunits.

The standard amino acids serve as raw materials for the manufacture of many other cellular products, including hormones and pigments. In addition, several of these amino acids are key intermediates in cellular metabolism.

Most plants and microorganisms are able to use inorganic compounds to make all the amino acids they require for normal growth. Animals, however, must get some of the standard amino acids from their diet to survive; these particular amino acids are called essential. Essential amino acids for humans include lysine, tryptophan, valine, histidine, leucine, isoleucine, phenylalanine, threonine, methionine, and arginine. They are found in adequate amounts in protein-rich foods from animal sources or in carefully chosen combinations of plant proteins.

In addition to the amino acids that form proteins, more than 150 other amino acids have been found in nature, including some that have the carboxyl and amino groups attached to separate carbon atoms. These unusually structured amino acids are most often found in fungi and higher plants.

Diagnosing AIDS

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Diagnosing AIDS involves some important tests. Physicians prefer to differentiate between people who have HIV infection and those who have AIDS. The Centers for Disease Control and Prevention (CDC), based in Atlanta, Georgia, recommends that physicians reserve the diagnosis of AIDS for HIV-infected people whose CD4 count falls below 200 cells per micro-liter of blood. A diagnosis of AIDS can also be made without confirmation of CD4 levels if someone who has no other reason for immune system damage develops an opportunistic disease. Diagnosing and treating AIDS is however a problem owing to the inability of scientist to give permanent remedy for the scourge.

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Aftermath of the Chernobyl’ Accident

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Abandoned town of Prypyat in Ukraine after the Chernobyl accident

The principal environmental effect of the aftermath of the Chernobyl’ accident has been the accumulation of radioactive fallout in the upper layers of soil, where it has destroyed important farmland. The second most important impact has been the threat to surface water and groundwater. The cleanup in some of the most heavily contaminated areas within the evacuation zone, such as Pripyat’, involved the stripping and burying of topsoil and vegetation, the sealing of wells, and the building of structures designed to prevent surface water from entering streams and rivers that drain into the Dnieper River system, which provides Kyiv’s water supply.

By most measures, the country most seriously affected by the accident is Belarus (which changed its name from Belorussia after it, along with the other Soviet republics, became independent with the collapse of the USSR in 1991). Almost 20 percent of the republic’s farmland was removed from production during the years immediately after the accident. Half of the vast 27,850-sq km (10,750-sq mi) area described as being ‘seriously contaminated’ by radiation (with levels of radioactive cesium in topsoil exceeding 5 curies) is in Belarus. The regions commonly identified as experiencing the greatest contamination include the oblasts (regions) of Homyel’, Mahilyow, and Brest in southern and eastern Belarus; Kyiv, Zhytomyr, and Chernihiv in northern Ukraine; and Bryansk in southwestern Russia.

Effects on public health have been more difficult to figure and are subject to much controversy. It is not always clear which health problems are caused directly by radiation and which are caused by poor nutrition, the general low level of health, and the anxiety and stress produced by fear of radiation exposure. These issues surround the debate over the causes of higher death rates among the more than half a million workers who participated in the Chernobyl’ cleanup.

However, at least one type of cancer can be attributed directly to Chernobyl’. There has been a significant rise in the incidence of thyroid cancer among children in the areas where radiation levels are highest. Thyroid cancer rates in Homyel’ Oblast, for example, increased 22-fold from 1986 through 1990 compared to the period from 1981 through 1985.

Many observers have argued that the accident at Chernobyl’ accelerated the transformation of the USSR toward a more open society. Soviet officials, unable to conceal the accident from the world, reluctantly acknowledged the accident during an evening news telecast in Moscow on April 28 and in brief newspaper accounts on April 30. This was followed by regular coverage focused on the cleanup efforts in the months that followed. This reporting sharply contrasts to the lack of coverage of earlier catastrophic events (an accident at a nuclear weapons plant in the Ural Mountains in 1957 and major earthquakes in Central Asia in 1948 and 1964).

Also, after the accident several key officials in the Soviet nuclear power industry were dismissed, punished, or both, and a new Ministry of Nuclear Power was created in 1986. Before then, officials in the general electric power ministry had overseen nuclear power. Chernobyl’ also called into question the basic safety of nuclear power in both the USSR and several Eastern European countries whose power plants contained reactors based on the RBMK reactor design used at Chernobyl’. (In the RBMK design, there is no containment shell, the graphite blocks used to moderate the fission reaction are flammable, and excess steam in the reactor core will cause the nuclear reaction to increase). As a result, international organizations, such as the International Atomic Energy Agency, became involved in programs to improve safety rules and upgrade the design of RBMK reactors in the USSR and Eastern Europe.

The accident, coupled with a general economic decline that set in during the last years of the USSR, also resulted in a dramatic scaling back of Soviet plans to use nuclear power to generate the bulk of electric power in Soviet regions remote from oil and gas energy resources. In Ukraine, opposition to further nuclear construction in the immediate post-Chernobyl’ years was particularly intense. In August 1990, for example, the Ukrainian parliament declared a moratorium on nuclear power plant construction. This ban was later lifted in 1993 because of severe energy shortages in Ukraine.

Earlier in 1990 the Ukrainian parliament had voted to close the Chernobyl’ plant permanently within five years, but closure was repeatedly postponed because of the country’s shortage of electricity-generating capacity. After a turbine fire in October 1991, the No. 2 reactor at Chernobyl’ was shut, leaving only two of the original four reactors at the plant in service. Reflecting mounting safety concerns in the international community, an agreement was concluded in April 1996 between the Ukrainian government and the G-7 countries (Group of Seven major industrial nations) to decommission the Chernobyl’ plant by the year 2000. In conjunction with the agreement, the G-7 countries pledged $300 million to finance programs to strengthen the sarcophagus, which some fear may collapse, and for more cleanup work. In November 1996, as part of the schedule for the decommissioning, the No. 1 reactor at Chernobyl’ was taken out of service, leaving only the third unit working. Finally, in December 2000 the plant was totally shut down. Although contained, the Aftermath of the Chernobyl’ Accident is one indicator of how dangerous nuclear power is whether for civilian or military purposes.

Efforts to Control Acid Rain and International Agreements

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Forest Damaged by Acid Rain

The Efforts to Control Acid Rain by International Agreements is often necessary to control its spread across borders. Acid rain typically crosses national borders, making pollution control an international issue. Canada receives much of its acid pollution from the United States—by some estimates as much as 50 percent. Norway and Sweden receive acid pollutants from Britain, Germany, Poland, and Russia. The majority of acid pollution in Japan comes from China. Debates about responsibilities and cleanup costs for acid pollutants led to international cooperation. In 1988, as part of the Long-Range Trans-boundary Air Pollution Agreement sponsored by the United Nations, the United States and 24 other nations ratified a protocol promising to hold yearly nitrogen oxide emissions at or below 1987 levels. In 1991 the United States and Canada signed an Air Quality Agreement setting national limits on annual sulfur dioxide emissions from power plants and factories. In 1994 in Oslo, Norway, 12 European nations agreed to cut sulfur dioxide emissions by as much as 87 percent by 2010.

Legislative actions to prevent acid rain have results. The targets established in laws and treaties are being met, usually ahead of schedule. Sulfur emissions in Europe decreased by 40 percent from 1980 to 1994. In Norway sulfur dioxide emissions fell by 75 percent during the same period. Since 1980 annual sulfur dioxide emissions in the United States have dropped from 26 million tons to 18.3 million tons. Canada reports sulfur dioxide emissions have been reduced to 2.6 million tons, 18 percent below the proposed limit of 3.2 million tons.

Monitoring stations in several nations report that precipitation is actually becoming less acidic. In Europe, lakes and streams are now growing less acid. However, this does not seem to be the case in the United States and Canada. The reasons are not completely understood, but apparently, controls reducing nitrogen oxide emissions only began recently and their effects have yet to make a mark. In addition, soils in some areas have absorbed so much acid that they contain no more neutralizing alkaline chemicals. The weathering of rock will gradually replace the missing alkaline chemicals, but scientists fear that improvement will be very slow unless pollution controls are made even stricter. International agreements however have aided various efforts to control acid rain around the world.

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Brønsted-Lowry Theory

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Relative Strenghts of Common Acids and Bases

A more satisfactory theory was proposed in 1923 by the Danish chemist Johannes Brønsted and independently by Thomas Lowry, a British chemist known as the Brønsted-Lowry Theory. Their theory states that an acid is a proton (hydrogen ion, H+) donor and a base a proton acceptor. Although the acid must still contain hydrogen, the Brønsted-Lowry theory does not need an aqueous medium. For example, liquid ammonia, which acts as a base in aqueous solution, can act as an acid in the absence of water by transferring a proton to a base and forming the amide anion (negative ion) NH2-: NH3 + base⇄NH2- + base + H+

The Brønsted-Lowry definition of acids and bases also explains why a strong acid displaces a weak acid from its compounds (and likewise for strong and weak bases). Here acid-base reactions are viewed as a competition for protons. In terms of a general chemical equation, the reaction of Acid (1) with Base (2) Acid (1) + Base (2)⇄Acid (2) + Base (1)results in the transfer of a proton from Acid (1) to Base (2). In losing the proton, Acid (1) becomes its conjugate base, Base (1). In gaining a proton, Base (2) becomes its conjugate acid, Acid (2). The equilibrium represented by the equation above may be displaced either to the left or to the right, and the actual reaction will take place in the direction that produces the weaker acid-base pair. For example, hydrogen chloride (HCl) is a strong acid in water because it readily transfers a proton to water to form a hydronium ion: HCl + H2O⇄H3O+ + Cl-The equilibrium lies mostly to the right because the conjugate base of HCl, Cl-, is a weak base, and H3O+, the conjugate acid of H2O, is a weak acid.

In contrast, hydrogen fluoride, HF, is a weak acid in water because it does not readily transfer a proton to water: HF + H2O⇄H3O+ + F-This equilibrium lies mostly to the left because H2O is a weaker base than F-, and because HF is a weaker acid (in water) than H3O+. The Brønsted-Lowry theory also explains why water can be amphoteric, that is, why it can serve as either an acid or a base. Water serves as a base in the presence of an acid that is stronger than water (such as HCl), in other words, an acid that has a greater tendency to dissociate than does water: HCl + H2O⇄H3O+ + Cl-Water can also serve as an acid in the presence of a base that is stronger than water (such as ammonia) according to Brønsted-Lowry Theory: NH3 + H2O⇄NH4+ + OH-

Cause of Aids

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The cause of AIDS could either be through infected syringes, sexual intercourse, sharing needles etc. AIDS is the last stage of a chronic infection with the human immunodeficiency virus. There are two types of this virus: HIV-1, which is the primary cause of AIDS worldwide, and HIV-2, found mostly in West Africa. Inside the body HIV enters cells of the immune system, especially white blood cells known as T cells. These cells orchestrate a variety of disease-fighting mechanisms. Particularly vulnerable to HIV attack are specialized “helper” T cells known as CD4 cells. When HIV infects a CD4 cell, it commandeers the genetic tools within the cell to manufacture new HIV virus. The newly formed HIV virus then leaves the cell, destroying the CD4 cell in the process. No existing medical treatment can completely eradicate HIV from the body once it has infected human cells.

The loss of CD4 cells endangers health because these cells help other types of immune cells respond to invading organisms. The average healthy person has over 1,000 CD4 cells per micro-liter of blood. In a person infected with HIV, the virus steadily destroys CD4 cells over a period of years, diminishing the cells’ protective ability and weakening the immune system. When the density of CD4 cells drops to 200 cells per micro-liter of blood, the infected person becomes vulnerable to AIDS-related opportunistic infections and rare cancers, which take advantage of the weakened immune defenses to cause disease.

Afro-Asiatic Language Family

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Throughout much of northern Africa, Afro-Asiatic language Family predominates. One branch of this language family is Semitic, which includes Arabic, as well as Amharic and Tigrinya, which are spoken in the Horn of Africa. The Cushitic branch extends south from the Red Sea coast, through the Horn of Africa, and into central Kenya and Tanzania. Its most commonly spoken languages are Somali and Oromo. The Chadic branch includes Hausa, widely spoken in Niger and northern Nigeria. Berber is yet a fourth branch of the Afro-Asiatic Language Family, and includes the language of the Tuareg of the Sahara as well as many other tongues spoken in and around the Atlas Mountains of northwestern Africa.

Agriculture in Afghanistan

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Agriculture in Afghanistan is mostly at the subsistence level. Only a very small share of Afghanistan’s land, mostly in scattered valleys, is suitable for farming, and a majority of this farmland requires irrigation. Water is drawn from springs and rivers and is distributed through surface ditches and through underground channels, or tunnels, which are excavated and maintained by a series of vertical shafts. Such a tunnel is known as a karez or qanat.

Wheat is the most important crop, followed by barley, corn, and rice. Cotton is another important and widely cultivated crop. Fruit and nuts are among Afghanistan’s most important exports. Afghanistan is noted for its unusually sweet grapes and melons, grown mostly in the southwest, north of the Hindu Kush, and in the fertile regions around Herāt. Raisins are also an important export. Other important fruits are apricots, cherries, figs, mulberries, and pomegranates.

Livestock is nearly as important as crops to Afghanistan’s economy. Karakul sheep are raised in large numbers in the north. The tight curly fleece of Karakul lambs is used to make Persian lamb coats. Other breeds of sheep, such as the fat-tailed sheep, and goats are also raised.

Afghanistan has long been a major supplier in the international drug trade. In the late 1990s Afghanistan replaced Myanmar (Burma) as the world’s biggest producer of opium, producing about 4,600 metric tons in 1999. Significant quantities of hashish were also produced in Afghanistan. In July 2000 the Taliban regime banned the cultivation of opium poppies, declaring that drug use was contrary to Islam. However, the ban ultimately raised opium prices on the international drug market, and the Taliban were widely suspected of profiting from the drug trade. With the collapse of law and order in 2001, many fields were sown with opium poppies, and Afghanistan again became the world’s largest supplier. Although the interim government of Afghanistan decreed the cultivation and processing of opium poppies illegal in early 2002, many impoverished local farmers remained financially dependent on the crop. Although agriculture in Afghanistan is a net income earner for the nation, there is a growing concern that the opium trade is fueling the insurgency by the Taliban.

Animal Life in Africa

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Africa teems with animal life of all shapes and sizes. The continent has thousands upon thousands of species of mammals, fish, reptiles, amphibians, birds, and insects. Many of these animals are linked in an intricate food web. For example, hippopotamuses deposit large amounts of nutrients in bodies of water where they rest and defecate; these nutrients support abundant growth of plants, insects, and other smaller creatures that in turn provide food for species higher in the food chain. Other animals are linked in symbiotic relationships, such as between big game animals and birds known as oxpeckers. These birds eat the ticks that pester the large animals. Animal life in Africa is often cut short by changing environmental conditions and illegal poaching due to either absence of conservation laws or inadequate implementation.

Efforts to Control Acid Rain and its implication on National Legislation

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A lot of Efforts to Control Acid Rain has been put in place around the world but its implication on National Legislation is another issue. In the United States, legislative efforts to control sulfur dioxide and nitrogen oxides began with passage of the Clean Air Act of 1970. This act established emissions standards for pollutants from automobiles and industry. In 1990 Congress approved a set of amendments to the act that impose stricter limits on pollution emissions, particularly pollutants that cause acid rain. These amendments aim to cut the national output of sulfur dioxide from 23.5 million tons to 16 million tons by the year 2010. Although no national target is set for nitrogen oxides, the amendments require that power plants, which emit about one-third of all nitrogen oxides released to the atmosphere, cut their emissions from 7.5 million tons to 5 million tons by 2010. These rules were applied first to selected large power plants in Eastern and Midwestern states. In the year 2000, smaller, cleaner power plants across the country came under the law.

These 1990 amendments include a novel provision for sulfur dioxide control. Each year the government gives companies permits to release a specified number of tons of sulfur dioxide. Polluters are allowed to buy and sell their emissions permits. For instance, a company can choose to cut its sulfur dioxide emissions more than the law requires and sell its unused pollution emission allowance to another company that is further from meeting emission goals; the buyer may then pollute above the limit for a certain time. Unused pollution rights can also be ‘banked’ and kept for later use. It is hoped that this flexible market system will clean up emissions more quickly and cheaply than a set of rigid rules.

Legislation enacted in Canada restricts the annual amount of sulfur dioxide emissions to 2.3 million tons in all of Canada’s seven easternmost provinces, where acid rain causes the most damage. A national cap for sulfur dioxide emissions has been set at 3.2 million tons per year. Legislation has been developed to enforce stricter pollution emissions by 2010.

Norwegian law sets the goal of reducing sulfur dioxide emission to 76 percent of 1980 levels and nitrogen oxides emissions to 70 percent of the 1986 levels. To encourage cleanup, Norway collects a hefty tax from industries that emit acid pollutants. In some cases these taxes make it more expensive to emit acid pollutants than to reduce emissions. Although a lot of Efforts to Control Acid Rain have been put in place, its implication on National Legislation would make certain efforts null and void especially where those laws do not apply to other countries.

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