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land area by 2032. The "World Atlas of Biodiversity: Earth's Living
Resources for the 21st Century" report said that as much as 48 percent of
these areas will become converted to agricultural land, plantations and
urban areas, compared with 22 percent today.
"By slowing the rate at which natural habitats are destroyed, GM
crops and other technologies that increase agricultural productivity can help
to preserve natural biodiversity," said Ammann of the University of Bern.
Bioethics: the future from a test-tube
More than forty years have elapsed since the discovery by James
Watson and Francis Crick of a "double spiral" — the DNA molecule.
Considerable headway has been made in the field of biology and gene
engineering since then, but there are a number of reasons holding back the
advance of these research studies. "Today we are in a position to cure
Alzheimer disease, but just one injection from a course costs about a
million French francs. Methods do exist, but all of them are linked to either
economic or ethical problems," admitted one participant in the session, the
Secretary-General of the Stockholm International Research Organization.
Laws on bioethics have been passed recently in several countries to
somehow adjust the problems that keep arising and to fix the framework
which research and practice must not transcend. But these laws vary from
country to country. For example, while laboratory tests on the human
embryo have been banned with rare exceptions in Germany, such
operations can be carried out in Britain but on the condition that the
embryo's age does not exceed two weeks.
It is obvious that the research studies being carried out in the field
of genetics cannot be halted - for their results will enable mankind to rid
itself of such diseases as haemophilia or inherited infantile paralysis. In the
view of Prof. Osuntokun of the University of Ibadan, Nigeria, the methods
of gene engineering will make it possible to wage an effective struggle
against tropical diseases which now plague the population of Third World
countries.
But, on the other hand, there is quite a number of warranted and
unwarranted apprehensions and questions. How should the law treat the
creation of chimeras and cloning? If impregnation "in vitro" exists, is there
moral justification for the bearing of the human foetus not by its natural
mother and even not by a human? Can use be made for such impregnation
of the frozen gene material of a deceased person? Is it possible to demand
and issue a patent for the human gene?
This is a far from complete list of questions now facing medics and
biologists, sociologists and jurists, philosophers and theologians. The
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International Committee on Bioethics, whose first session took place in
Paris, was created under UNESCO's aegis precisely for the purpose of
elaborating a universal approach for different cultures and peoples towards
the problem of the human genome. The list of participants in this committee
is too long. Suffice to say that it includes three Nobel laureates (Sydney
Altaian, Christian de Duve and Jean Dausset), also represented on it,
besides biologists and medics, are jurists, economists, sociologists, writers
and even a spokesman for the Vatican. The principles on which it is going
to build its activities were expressed most aptly, perhaps, by Dr. Michel
Renel of the world-famous Weizmann Institute of Science in Israel which
uses genetic means to combat cancer: "Man is not a creature which is
determined merely by a collection of genes, it is impossible to see this alone
and forget that first and foremost he is determined by culture"62.
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Text 7. The Nucleus, Genetic Information and Its Transmission
Genetic information is the set of data determining the structural and
functional properties of cells. Genetic information is stored in the cell
nucleus, in molecules of DNA (or, more accurately, in the sequence of
nucleotides in these DNA molecules) and it serves the cell as a guide to act
in different situation. After cell division it controls the synthesis of
structural proteins and enzymes required for cell function; it takes part in
growth and cell differentiation. In differentiated cells it participates in the
regulation of metabolic processes (induction and repression).
The site of genetic information in a cell is the nucleus or, in
prokaryotic cells and autonomous cell organelles, the circular chromosome.
The nucleus is a morphologically distinct organelle separated from the
cytoplasm by the nuclear membrane. It is in fact a double membrane
involuted so as to form pores with apparent diameter of 3C to 100 mm
through which macromolecules can pass when necessary. In addition to this
unique structure, the nuclear membrane participates directly in the
replication of DNA and may communicate with the extracellular medium.
Much of the nuclear material is in fact deoxyribonucleic acid (DNA) which,
in an interphase nucleus, forms filaments of variable thickness (10 mm on
the average but occasionally only 2 mm). The thickness of these filaments
depends on the presence or absence of proteins surrounding the double
helix of DNA. The length of these filaments depends on the molecular
weight of DNA, one chromosome (about 1010 molecular weight) containing
DNA several cm long. The DNA content of the nucleus depends on the
animal species (about 6 pg per mammalian cell) and is rather constant in
different cells, of a given species.
Ribonucleic acids (RNA) accumulate mainly in the nucleolus,
enclosed in the nuclear membrane. Their size and function will be described
in the following chapter.
Nuclear proteins can be divided into histones and nonhistone
proteins. Histones are classified into five groups differing by size, charge
(always positive) and amino acid composition. Their function consists in
organizing the long filaments of DNA into more compact forms
(superhelix). This is accomplished by electrostatic interaction of histones
with the negatively charged phosphate groups of DNA. The composition of
non-histonc proteins is not fully known hut they appear to be
phosphorelated, acidic proteins. They are responsible for a selective and
transient inhibition of RNA transcription through binding to certain
segments of DNA and for regulating the transcription of histone genes.
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Besides the macro molecules, the nucleus contains low-molecular
weight compounds and ions, especially Mg2+ and K+.
DNA molecules are polynucleotides, i.e. chains composed of
mononucleotides. The principal backbone of DNA molecules is formed by
a sequence of deoxyribose molecules alternating with phosphate residues,
linked by diester bonds in such a way that the 5'-OH group of deoxyribose
molecules is esterified by phosphoric acid which is attached to the 3'-OH
group of deoxyribose of the neighboring nucleotide. DNA molecules
contain pyrimidine bases thymine T, cytosine C) and purine bases (adenine
A, guanine G). These bases are attached to the C1 of deoxyribose by a N-
glycosidic bond to N3 of pyrimidines and to N9 of purines. The base
sequence is highly specific for every DNA molecule.
In solution, DNA molecules assume the structure of a double helix
(Watson and Crick). The strands are connected with each other through
hydrogen bonds formed between juxtaposed bases A-T (two hydrogen
bonds) and C-G (3 hydrogen bonds); they are stabilized by hydrophobic
interactions between neighboring bases of the same strand; the double-helix
structure is supported longitudinally by molecules of basic proteins which
are localized in the groove of the double helix.
In addition to the double-stranded form there, exist DNA's in the
form of a closed circle, either one or several arranged like links in a chain
(in mitochondria, bacteria, viruses). In a chromosome, a supercoil (a coiled
double helix) is formed to achieve maximum condensation of material.
DNA molecules are synthesized from deoxyribonucleotides in the
presence of a template (i.e., one of the DNA strands whose nucleotide
sequence will be exactly reproduced step by step) and of enzymes. DNA
biosynthesis requires sufficient supply of all the deoxyribonucleotides
(dTTP, dATP, dGTP, dCTP)63.
63
Мельникова В.А., Барановская М.Е., Халикова Д.Г. Microbiology and
Biotechnology. Указ. соч.
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Text 8. Principles of Metabolic Control
Cells and organisms are relatively isolated systems in a quasisteady state. The functions of living organisms as a whole as well as of their
parts are regulated with the objective of attaining maximum survival. Since
the living system reacts in space and time, both spatial and temporal
regulation may be employed.
Space comes into play mainly in the higher degree of organization
of structures; maintenance of structural stability of proteins, association of
cooperating enzymes into multienzyme complexes, their localization in
definite compartments (mitochondria, endoplasmic reticulum) and
specialization of cells and tissues by differentiation processes.
Time is involved in regulation mainly in terms of modification if
reaction rates (metabolic, transport, and others). In practice, both
dimensions are utilized simultaneously.
Regulatory mechanisms become effective at very different levels of
organization but their basis is always molecular. Functions of an organism
can be regulated through reactions taking place in cells (metabolic
regulation) and at the level of the whole organism (hormonal, nervous
controls). Within a cell, metabolic "processes are controlled mainly by
regulating the activity of individual enzymes.
Enzymes can be regulated in several ways:
1. By changing the concentration of substrates or coenzymes (a
metabolic signal) that result in changes of enzyme activity, the amount of
the enzyme involved remaining constant. Changes in the concentration of a
signal compound are mostly achieved through compartmentation, i.e. by
forming membranes separating the cell from the extracellular milieu and
smaller compartments within the cell, these being separated spatially (by
membranes) or functionally (carriers).
2. By changing the concentration of effectors (activators and
inhibitors) in allosteric enzymes. By interacting with the allosteric site of
the enzyme, such effectors can increase or decrease the enzyme activity on
the basis of cooperative changes of conformation of the subunits, from
which the enzyme is composed. The amount of the allosteric enzyme is not
changed during the process.
3. By induction or repression when, in contrast with the
two preceding mechanisms, the amount of enzyme and hence its total
activity in the system is changed. The enzyme quantity per cell depends on
presence of a represser protein which is coded by a regulator gene and
which, in its active form, inhibits the synthesis of some enzymes
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(repression). Some low-molecular weight compounds (inducers) can
interact with the represser and change it to an inactive form which cannot
inhibit the synthesis of the given enzyme — this is the induction of their
synthesis (derepression).
Multi-enzyme systems are those in which the individual enzymes
are organized in such a way that the product of one enzyme reaction serves
as substrate for the next. Here again, feedback regulation plays an important
role, a product of a reaction sequence controlling the activity of one of the
preceding enzymes, usually the first of the sequence.
Regulation at the level of an organism requires the existence of
special differentiated cells and structures with control function (nerve cells,
endocrine glands). These cells are known to produce certain compounds
that can be considered as material carriers of information, signals that are
transported from one part of the organism to another.
Nervous regulation is mediated by a system of glial cells mutually
interconnected through hollow and very long projections, ll addresses itself
to a special receptor, it is very rapid but it cannot embrace all cells of the
organism. The molecular basis of this type of regulation are changes in ion
concentrations inside and outside the nerve cells which initiate and
propagate the transmission of nerve impulses. The impulse is transmitted to
another cell at the end plate through molecular mediators.
The molecular basis of hormonal regulation are hormones which
can reach all cells of the organism and affect their function but only some
cells (those of the target tissues) are receptive to the hormonal stimulus
specifically. To increase the efficiency of regulation, hormones are often
transported from the cell of origin to the target tissue in association with a
specific protein. Such regulation is slower than the nervous one but it may
affect any cell in the organism provided it has the proper receptor. It is
assumed that the basic process of hormonal regulation is the binding of the
hormone to a surface receptor protein or to a component of the cytoplasm.
The central nervous system is superior to the other parts of
nervous communications as well as to hormonal regulation because it can
store information transmitted by the signals into a memory, into specific
structures of glial cells, and to use this information whenever necessary64.
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Biotechnology. Указ. соч.
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Text 9. Essential Fatty Acids
Polyunsaturated fatty acids with 20 carbon atoms exhibit unique
physiological activities in the human body, for example lowering of
cholesterol and triacylglycerols in plasma, prevention of atherosclerosis and
other cardiovascular diseases and reduction of collagen-induced
thrombocyte aggregation. Moreover, these fatty acids are of great value in
the nutrition of edible marine animals reared in man-culture, and as
precursors of eicosanoid hormones. Potential sources of such fatty acids
include fungi, mainly lower Phyco-mycetes, microalgae, viz.
dinoflagellates, diatoms and unicellular red algae, marine macroalgae,
particularly Phaeophyta and Rhodophyta, and mosses. The biomass may be
enriched with Cao-polyunsaturated fatty acids by chilling, nitrogen
starvation, controlled illumination and incubation with lipophilic
compounds.
Polyunsaturated fatty acids, especially those with 20 carbon atoms,
are currently receiving attention in view of their physiological, industrial
and pharmaceutical value. So far, these fatty acids are obtained from
animals, e.g. fish oil, which makes their large-scale preparation rather
uneconomical. Within the past decade much work has been done on
polyunsaturated fatty acids in a variety of microorganisms and lower plants.
The major objectives of the present article are to review these studies and
discuss the biotechnological potential for providing an economical source
of these valuable compounds.
The designation "essential" is related to mammals and, more
precisely, to man. The mammalian route of fatty acid biosynthesis is more
limited than that of plants and microorganisms. This is true as far as
polymerization and desaturation reactions are concerned. Thus, it is known
that condensation of C2-units in mammals occurs only up to the C18-stage.
Furthermore, double bonds can be subsequently introduced at only four
positions, ∆4, ∆5, ∆6 and ∆9. Mammals lack the ability to introduce any
double bonds at carbon atoms between C-9 and the terminal methyl group.
This implies that such living systems cannot synthesize linoleic (18:2 ∆9,
∆12 or ω6; ω designates counting from the methyl group) and linolenic
(18:3 ∆9, ∆12, ∆15 or ω3) acids. These two fatty acids are however, needed
by mammals, and must be supplied in their diet, hence the term
"essential"65.
65
Мельникова В.А., Барановская М.Е., Халикова Д.Г. Microbiology and
Biotechnology. Указ. соч.
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Part 7. ПРАКТИКУМ ПИСЬМЕННОГО ПЕРЕВОДА
История биотехнологии
Впервые термин «биотехнология» применил венгерский
инженер Карл Эреки в 1917 году.
Случаи использования в промышленном производстве
микроорганизмов или их ферментов, обеспечивающих
технологический процесс, известны издревле, однако
систематизированные научные исследования позволили существенно
расширить арсенал методов и средств биотехнологии.
Так, в 1814 году петербургский академик К. С. Кирхгоф
(биография) открыл явление биологического катализа и пытался
биокаталитическим путём получить сахар из доступного
отечественного сырья (до середины XIX века сахар получали только
из сахарного тростника). В 1891 году в США японский биохимик Дз.
Такамине получил первый патент на использование ферментных
препаратов в промышленных целях: учёный предложил применить
диастазу для осахаривания растительных отходов.
В начале XX века активно развивалась бродильная и
микробиологическая промышленность. В эти же годы были
предприняты первые попытки наладить производство антибиотиков,
пищевых концентратов, полученных из дрожжей, осуществить
контроль ферментации продуктов растительного и животного
происхождения.
Первый антибиотик — пенициллин — удалось выделить и
очистить до приемлемого уровня в 1940 году, что поставило новые
задачи: поиск и налаживание промышленного производства
лекарственных веществ, продуцируемых микроорганизмами, работа
над удешевлением и повышением уровня биобезопасности новых
лекарственных препаратов66.
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138
Биотехнология
Термин «биотехнология» был введен в 1917 г. венгерским
инженером Карлом Эреки и характеризовал все виды работ, при
которых из сырьевых материалов с помощью живых организмов
производятся те или иные продукты. По определению академика А.А.
Баева (1984), биотехнология – это использование живых организмов и
их систем в промышленных целях. Поэтому несмотря на то, что
большие материальные затраты и длительное время уходит на
фундаментальные исследования, основной целью биотехнологии
является получение коммерческого продукта, рентабельного
производства и, следовательно, того, что необходимо людям в
большей или меньшей степени.
Биотехнология формировалась как междисциплинарная наука и
является на сегодняшний день самостоятельной, интенсивно
развивающейся отраслью. Ее биологическая составляющая относится
к сфере промышленной микробиологии и биохимии, а молекулярная –
к областям молекулярной биологии, молекулярной генетики и
энзимологии нуклеиновых кислот. Благодаря этому сочетанию
сталовозможным более детальное изучение внутриклеточных
процессовклетки, систем наследования и экспрессии генов.
Усовершенствование методов клеточной и молекулярной
биотехнологии позволило управлять наследственностью и
жизнедеятельностью животных, растений и микроорганизмов,
создавать организмы с новыми полезными для человека свойствами,
ранее не наблюдавшимися в природе.
На сегодняшний день выделяют три основных направления
биотехнологии: промышленная биотехнология (промышленная
микробиология), культура растительных и животных клеток и тканей
и генная инженерия.
Отдельные биотехнологические процессы, используемые в
различных сферах практической деятельности человека, известны с
древних времен. К ним относятся хлебопечение, виноделие,
приготовление кисломолочных продуктов и т. д. В большинстве этих
процессов используются микроорганизмы. Быстрый рост и огромное
генетическое разнообразие микроорганизмов позволяют за короткий
промежуток времени осуществить синтез больших количеств
требуемого продукта в строго контролируемых условиях67.
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Достижения биотехнологии
С помощью методов генной инженерии (перенос чужеродных
генов, придающих новые полезные свойства организму хозяина)
удалось видоизменить структуру и содержание современной
промышленной микробиологии. Во-первых, существенно повысилась
продуктивность промышленных микроорганизмов – продуцентов
классических продуктов путем введения дополнительных генов,
увеличения их количества или активности. Во-вторых, вводя в
микробную клетку новые гены, удалось изменить питательные
потребности микроорганизма. При стимулировании микроорганизмов
к синтезированию несвойственных им веществ увеличили
разнообразие биотехнологической продукции – некоторые белки
человека, клонированные в микробной клетке, интерфероны,
интерлейкины а также инсулин находят в настоящее время
терапевтическое применение. Аналогичными методами стало
возможным преобразование клеток бактерий, дрожжей и
млекопитающих в «фабрики» для масштабного производства
антибиотиков, белков, жиров, аминокислот, а также для получения
безопасных и дешевых вакцин.
Уже 2002 г. в мире получено разрешение на применение более
30 лекарственных препаратов, созданных методами генной
инженерии. В стадии клинического изучения находится более 100
биопрепаратов, еще более 500 – на стадии разработки, причем
большинство из них предназначены для лечения болезней, которые до
настоящего времени считались неизлечимыми.
По подсчетам специалистов, ежегодный объем мирового
фармацевтического рынка составляет около 402 млрд долларов (2000
г.) и постоянно растет. Большая часть коммерческих разработок в
области молекулярной биотехнологии приходится на США (French
Biotechnology Industry Association, 2002). Единственным конкурентом
США в этой области сегодня можно считать Китай. Это связано с тем,
что правительство Китая объявило биотехнологию «стратеги- ческой
индустрией» и национальным приоритетом. Интенсивное развитие
биотехнологических компаний в Китае сохраняется и к настоящему
моменту (SciDev.Net, 20 декабря 2004 г.)68.
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