Биология в современном мире. Учебное пособие

The motor functions of the nervous system employ peripheral nerves that carry impulses from the central nervous system to responsible parts called effectors. These effectors are outside the nervous system and include muscles that contract when they are stimulated by nerve impulses, and glands that produce a secretion when they are stimulated.

Thus the nervous system can detect changes occurring in the body, make decisions on the basis of the information received and cause muscles or glands to respond. Typically, these responses are directed toward, counteracting the effects of the changes, and in this way, the nervous system helps maintain homeostasis. The nervous tissue of the brain and spinal cord consists of masses of nerve cells or neurons that are the structural and functional units of the nervous system. These cells are specialized to react to physical and chemical changes occurring in their surroundings. They also conduct nerve impulses to other neurons and to cells outside the nervous system. Neurological cells are accessory cells within nervous tissue. They greatly outnumber the neurons and in addition to providing for certain physiological needs of the neurons, they function much like connective tissue cells in other body structure that is they fill spaces and surround or protect various parts.

Answer the questions:

1)What groups are organs of the nervous system divided into?

2)What functions does the nervous system provide?

3)What are receptors (effectors)?

4)What cells does the nervous tissue of the brain and spinal card consist

of?

5) What is the function of neurons?

А.4 The immune system of a human being.

Every person goes trough life surrounded by potentially harmful microorganisms. Those that invade the body are usually held at bay (to hold somebody at bay – держать кого-либо в страхе) by the body’s immune defences, an elaborate system that stands guard to intercept and destroy foreign cells. It is

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therefore a matter of great biological and medical significance that the system sometimes goes awry (to go awry – работать неправильно, давать сбои) in such a way as to give rise to the diverse group of disorders known as autoimmune diseases. Such disorders result when the immune system which originally distinguishes self from nonself with great precision begins to attack certain of the body’s own cells.

The immune system is believed to have evolved from the need of the most primitive multicellular organisms to recognize other cells of the same kind. A further communication network among cells was needed in order for cells to cooperate in the development of specialized organs. A requirement of these recognition mechanisms was the general ability to discriminate between self and nonself and that task became the special duty of the immune system now found in all vetebrate animals. In the course of evolution the system took on a second but equally important function: the elimination of any foreign cells that enter the body.

The abilily to distinguish self from nonself applies not only to invading microorganisms and parasites but also to foreign molecules including those with no harmful properties. The body will reject even nourishing proteins if they originate in alien (чуждый) sources unless these large molecules are first broken down by enzymes in the gut. Only then can they be absorbed through the intestinal wall in the form of amino acids, their primary building blocks, and resynthesized into proteins that are uniquely the body’s own.

The immune system also rejects cells from other individuals of the same species unless the cells are identical with the body’s own. In the case of the relatively simple red blood corpuscles it is fairly easy to match the donor’s blood with recipient’s, so that a transfusion can be carried out with minimal risk. Must tissue cells with a cell nucleus (which red cells lack) are more difficult to match which is why the transplantation of a kidney is a much more demanding procedure than blood transfusion, usually requiring that the immune apparatus of the patient be crippled (to cripple – приводить в негодность) with suppressive drugs.

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Human beings and other animals pay a high price in many other ways for their zealous (усердный, рьяный) protection of biological individuality. For example, the same mechanisms the body relies on to avoid immunological responses to its own cells sometimes allow cancerous cells to escape (избегать) destruction. The differences between normal and cancerous cells of the same individual may be so subtle (неуловимый) that the immune system fails to detect them. On the other hand, it is thought that the immune system does attack malignant cells if they are significantly different from normal ones.

The main functions of the immune system can thus be summarized as follows: (1) resistance to foreign cells and substances that may cause trouble and

(2) searching out cancerous cells that may arise from time to time. Both of these functions require an effective recognition mechanism to distinguish self from nonself. It is the errors of this system in turning against the self, diving rise to immunological attack on the body’s own cells and tissues, that are a subject of intense interest and study among biologist and physicians.

Answer the questions:

1)What is the special duty of the immune system?

2)Why does the immune system reject cells from other individuals of the same species?

3)What are the main functions of the immune system?

А.5 Vitamins.

Vitamins are organic compounds (other then carbon, lipids and proteins) that must be present in small amounts for normal metabolic processes but cannot be synthesized in adequate amounts by body cells. Thus they are essential nutrients that must be supplied in foods. Vitamins can be classified on the basis off their solubility (растворимость), since some are soluble in fats (or fat solvents) and others are soluble in water. Those that are fat-soluble include vitamins A, D, E and K; the water soluble group includes the B vitamins and vitamin C.

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Fat-soluble vitamins. Since the fat-soluble vitamins dissolve in fats they occur in association with lipids and are influenced by the same factors that affect lipid absorption. For example, the presence of bile salts in the intestine promotes the absorption of these vitamins. As a group the fat-soluble vitamins are stored in moderate quantities within different tissues and because they are fairly resistant to the effects of heat they are usually not destroyed by cooking or food processing.

Vitamin A occurs in several forms, including retinol and retinal. This vitamin can be synthesized by body cells from a group of yellowish plant pigments called carotenes. Whenever vitamin A or its precursors are present in excess, they are stored mainly in the liver which regulates the concentrations of these substances within the body.

Vitamin A is relatively stable to the effects of heat, acids and alkalis but it is readily (легко) destroyed by oxidation and is unstable in the presence of light. Although the functions of vitamin A are not fully understood, it is known that retinal is used in the synthesis of rhodopsin (visual purple) in the rods of the retina. Vitamin A is thought to be required for the production of light-sensitive pigments in the cones as well. Thus, this vitamin is needed to maintain normal vision. It is also believed to function in the synthesis of mucoproteins of mucus, in the development of normal bones and teeth and in the maintenance of epithelial cells in skin and mucous membranes.

Vitamin A as such is obtained only from foods of animal origin such as liver, fish, whole milk (цельное молоко), butter and eggs. However its precursor, carotine is widespread in leafy green vegetables and in yellow or orange vegetables and fruits.

Vitamin D is a group of steroids that have similar properties. One of these substances, vitamin D3 is found in food such as milk, egg yolk and fish liver oils. Vitamin D2 is produced commercially by exposing a steroid obtained from yeasts to ultraviolet light. Vitamin D can be synthesized from dietary cholesterol that has been converted to provitamin D by intestinal enzymes, then stored in the skin and exposed to ultraviolet light.

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Like other fat-soluble vitamins, vitamin D is resistant to the effect of heat, and to oxidation, acids and alkalis. It is stored primarily in the liver and occurs to a lesser extent (в меньшей степени) in the skin, brain, spleen and bones. Vitamin D is released into the blood and is converted in the kidneys into its active form. This form in turn is carried as a hormone in the blood to the intestine where it promotes the absorption of calcium and phosphorus, and, thus, helps ensure that adequate amounts of these minerals are available in the blood for tooth and bone formation and various metabolic processes.

Although natural foods are generally poor sources of vitamin D, it is often added to food during processing. For example, homogenized milk, non-fat milk, evaporated (сгущенное) milk are typically fortified (обогащено) with vitamin D.

Vitamin E includes a group of compounds. The most active of these is alphatocopherol. This substance is resistant to the effects of heat, acid and visible light, but is unstable in alkalis and in the presence of ultraviolet light or oxygen. In fact, it combines so readily with oxygen that its presence may prevent the oxidation of other compounds, and for this reason it is said to be an antioxidant.

Although vitamin E is found in all tissues, it is stored primarily in the muscles and adipose tissues. It also occurs in relatively high concentrations in the pituitary and adrenal glands.

The precise functions of vitamin E are unknown, but it apparently plays a role as an antioxidant by inhibiting the oxidation of vitamin A in the digestive tract and of polyunsaturated fatty acids in the tissues. It may also help maintain the stability of cell membranes.

While vitamin E is widely distributed among foods, its richest sources are oils from cereal seeds such as wheat germ oil. Other good sources are salad oils, margarine, shortenings (жиры), fruits, nuts and vegetables. Since this vitamin is so easily obtained, deficiency conditions are rare.

Answer the questions:

1)What are vitamins?

2)Distinguish between fat-soluble vitamins and water-soluble vitamins?

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3)What substance is used by body cells to synthesize vitamin A?

4)What conditions will destroy vitamin A?

5)What foods are good sources of vitamin A?

6)Where is vitamin D stored?

7)What are the functions of vitamin D?

8)What foods are good sources of vitamin D?

9)Where is vitamin E stored?

10)What are the functions of vitamin E?

11)What foods are good sources of vitamin E?

А.6 Render in English.

Водорастворимые витамины.

Витамин С играет важную роль в обменных процессах, особенно в усвоении белков, в поддержании нормального состояния соединительной ткани и в восстановлении тканей. При недостатке витамина С увеличивается проницаемость стенок кровеносных сосудов, нарушается структура хрящевой и костной тканей. В организме человека витамин С не образуется и отсутствуют его накопления. Необходимое количество витамина С должно поступать с пищей. Основные источники витамина С – овощи, фрукты и ягоды. Повседневная потребность в этом витамине удовлетворяется за счет капусты, картофеля, зеленого лука, томатов. Много витамина С содержится в зеленом сладком перце, красном перце, лимонах, апельсинах и др.

Природным его концентратом является шиповник. Сушеные плоды шиповника служат прекрасным источником витамина С, особенно зимой и весной.

Витамин С получают также синтетическим путем: его выпускают в виде порошка, драже, таблеток. Нагревание продуктов, содержащих витамин С, сокращает наличие витамина С или даже полностью его разрушает.

Витамины группы В включают наиболее важные для человека В1, В2, В3, В6 и В12.

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Витамин В1 играет важную роль в обмене углеводов, поступает в организм с пищей и частично образуется микроорганизмами в кишечнике.

Содержится в дрожжах, в хлебном квасе, в зерновых культурах, особенно в отрубях, в печени, почках, сердце животных.

Витамин В2 участвует в процессах роста, в обмене белков, жиров и углеводов, оказывает влияние на состояние нервной системы. Поступает в организм с пищей: яйцами, сыром, молоком, мясом, зерновыми культурами,

дрожжами и молоком. Этот витамин разрушается под воздействием ультрафиолетовых лучей. Потери витамина В2 при кулинарной обработке невелики.

Витамин В3 участвует в реакциях клеточного дыхания, в белковом обмене, нормализует работу кишечника и всего пищеварительного тракта.

Поступает в организм с мясом домашней птицы, говядиной, печенью,

почками, дрожжами. Этот витамин стоек к кулинарной обработке, к

воздействию света, кислорода, воздуха, щелочей.

Витамин В6 обеспечивает нормальное усвоение белков и жиров.

Содержится в продуктах растительного и животного происхождения (в сухих дрожжах, картофеле, курятине, говяжьей печени, яйцах, молоке). В

достаточном количестве также образуется кишечными бактериями в организме человека. Устойчив к воздействию кислот и высоких температур.

Причем нагревание для него даже полезно, т.к. при этом освобождаются его активные компоненты.

Витамин В12 имеет высокую биологическую активность. В этом витамине нуждаются все животные организмы. Участвует в процессе кроветворения. Поступает в организм с пищей и синтезируется микроорганизмами кишечника. Содержится в основном в говяжьей печени. В

промышленности его получают на основе микробиологического синтеза.

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А.7 A quicker way to clone.

For years scientists have to unravel (разгадать) the mysterious of how genes put their complex and indelible (несмываемый) stamp on the lives of humans and other living organisms. In laboratories across the country scientists scramble (продираются) to identify the missing links in the chain of more than 100,000 estimated human genes. While the world awaits further advances that will bring the human genome into shaper focus, a group of scientists has made an important genetic advance – an entirely new way to clone genes and parts of chromosomes that may put the scientific community a few notches (уровень) closer to understanding the role genes play in human disease.

Geneticists (USA & Russia) have developed a new technique for swiftly isolation and cloning specific fragments of human genetic material directed into yeast cells. The resulting yeast artificial chromosomes (YACs) are engineered through a process known as transformation – associated recombination (TAR). According to the scientists TAR cloning captures the ability of yeast to recombine pieces of DNA during transformation (the time during which DNA material is being introduced to a cell). The traditional task of isolating and cloning DNA material involves randomly (наугад) cutting DNA from cells into thousands or even millions of individual pieces. Each piece has to be treated so that it can be cloned into yeast or bacteria. Once cloning is complete, each fragment must be analyzed to find the desired fragment orgene. With TAR cloning scientists can rely on the yeast to find the precise sequence of interest. Yeast has the ability to find the same or related molecules and when it finds them, it also has the ability to join them to others. This uncanny (сверхъестественный) ability to find and combine similar DNAs is independent of whether the DNAs originate in humans, animals or plants. Human DNAs are introduced, or transformed, into yeast cells accompanied by a tiny piece of the gene or fragment that is ultimately desired. Only DNA that contains a region that matches that tiny piece is maintained, or cloned, as the yeast cells reproduce. So far DNA regions have been isolated from chromosomes regions that harbor several known disease genes. TAR cloning opens the door

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cloning specific genes or other chromosome segments that are related to disease. The scientists think that TAR cloning might provide opportunities to more rapidly get many copies of cells. They also foresee that this would be very useful in characterizing the genes that play a role in responses to genotoxins, either making them more susceptible (восприимчивый) or enabling them to deal with damage better.

Answer the questions:

1)What was an important genetic advance made by Russian and American geneticists?

2)What kinds of plant did they use to clone specific fragments of human genetic material?

3)What is the main ability of yeast cells ?

4)What is the task of TAR cloning ?

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Учебное пособие

Алла Юрьевна Богомолова Ольга Владимировна Кабанова

БИОЛОГИЯ В СОВРЕМЕННОМ МИРЕ

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