Download Las proteínas funcionan uniéndose en forma específica a

Guía de Trabajos Prácticos - Inglés I - Cátedra de Inglés Técnico
Facultad de Bioquímica y Ciencias Biológicas - Universidad Nacional del Litoral
UNIDAD V
PASADO PERFECTO (VOZ ACTIVA Y PASIVA)
EJEMPLOS: 1- Several hundred years of effort had previously failed to produce a reliable poisoning
method with experimental and research purposes. Researchers had been successful in
developing alternative methods, but no fully-satisfactory ones were available.
2- Until that time, researchers had reported little comparative work on methods for precisely
determining water hardness.
3- Mutants had been selected with a lack of genetic control. Such mutants had been changed
and the genetic mechanism was no longer sensitive to a particular controlling metabolite.
PASADO PERFECTO CONTINUO
EJEMPLOS: 1- Glutamic acid fermentation processes had been offering an actual example of genetic
control in chemical production.
2- During the whole process, the reaction rate had been controlling the substance diffusion
from the solution to the enzymatically active surface.
FUTURO SIMPLE
EJEMPLOS: 1- The lead in the tissues will vary in accordance with a definite pattern.
2- In the future, the world’s natural food resources will run out partially; we will find
ourselves faced against the problem of replacing natural food resource contribution to
our supply.
3- Physical methods to determine the molecular weights of highly purified proteins will be
described later.
4- Cell differentiation will be better understood after discussing the detailed structure of
cell and embryo development in the following chapters.
FORMA “GOING TO”
EJEMPLOS: 1- A mixture of antigens is going to produce several species of antibodies, one for each
protein.
2- More and more liquid is going to be added to the vessel to increase the liquid volume
and decrease that of the vapour.
3- Nitrogen-fixing microorganisms are not going to operate successfully in damp
conditions.
4- Is a person with low metabolic rate going to have a tendency to get fat?
COORDINANTES
FOR-YET
1. We do not understand the equation, for it is difficult.
2. We understand the equation, yet it is difficult.
3. In cyanide intoxication, the oxidative enzyme systems are apparently not destroyed, for the inhibitory
effect of hydrogen cyanide can be reversed when a mechanism for binding the cyanide more or less
firmly is introduced.
4. Absorption of hydrogen sulfide has been demonstrated and discoloration of the skin reported, yet this
is not a significant source of systemic poisoning.
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Guía de Trabajos Prácticos - Inglés I - Cátedra de Inglés Técnico
Facultad de Bioquímica y Ciencias Biológicas - Universidad Nacional del Litoral
BUT
1. He has not titrated the solution, but he has prepared the reagents.
2. Such mechanism could explain the absence of bacteria, but evidence to support of disprove this
hypothesis is lacking.
AND
1. He has prepared the reagents and titrated the solution.
2. The researchers have studied nitrite oxidation in detail and found oxygenase-linked intermediate
stages.
3. Within a few days, destruction of the red cells may progress to the point where death occurs from
anoxemia, and may be considered a form of chemical asphyxia.
SO
1. Liquid extraction has conventionally been considered a newer operation, so its kinetics will be
normally discussed only in terms of new diffusion equations for both phases.
2. In combination with water, ethylene oxide does not have an appreciable vapour pressure so, unlike
most other vapours and gases, practically all the gas in the lungs is completely absorbed and
practically none is exhaled.
NOR
1- Sometimes, the best culture medium cannot be chosen, nor the best product can be obtained because
there are some practical disadvantages in using optimum production conditions.
2- The slime molds are not classified as true fungi; nor do they possess any resemblance with ameboid.
are they considered similar to ameboid protozoa.
can they be considered similar to ameboid protozoa.
COORDINANTES DE A PARES
 These organisms can use organic compounds either as a sole photosynthetic carbon source or in
conjunction with CO2.
both
and
 Among phototrophs, carotenoid composition is both complex and group specific.
not only
but (also)
neither
nor
1- Members of this subgroup either oxidize ammonia to nitrite or nitrite to nitrate; none can oxidize both
these reduced nitrogen compounds.
2- Neither elementary arsenic nor arsenic sulfide is considered very toxic.
3- The cyanides undergo relatively rapid decomposition or modification in the body; they either combine
with sulfur to form thiocyanate or are excreted as such through the lungs, in the saliva and in the
urine.
4- In the case of nonoccupational illnesses among industrial workmen, the physician will have to make
every effort not only to convict or exclude lead as an etiologic or contributory factor in an illness, but
also to demonstrate the actual nature of the disease in question.
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Guía de Trabajos Prácticos - Inglés I - Cátedra de Inglés Técnico
Facultad de Bioquímica y Ciencias Biológicas - Universidad Nacional del Litoral
NO CONFUNDIR CON:
Both methods are equally useful; either (of them) will provide accurate pH values.
Both methods are quite inaccurate: neither (of them) will provide useful results.
CONECTORES
EJEMPLOS: 1- Some elements (viz., tin, copper) are not among the commonest ones in the Earth’s
crust; however, they are widely used.
2- One sample of milk is not identical, in either properties or composition, to another
sample. Milk, therefore, cannot be classified as a substance.
3- Solubility decreases with an increase in temperature; moreover, it varies directly with
the partial pressure of the gas.
4- This chance discovery of the relationship between electricity and magnetism led quickly
to the invention of the electric dynamo; besides, it laid the basis for modern electromagnetic field theory.
5- The first law of thermodynamics was put forward by Mayer in 1842. Meanwhile, James
Joule made exact determinations of the mechanical equivalent of heat.
EJERCITACIÓN
I)
A partir del texto siguiente, realice la ejercitación propuesta:
This is very important because it is more difficult to determine the structure of floppy molecules and, in
order to study the structures as individuals, the pentamers have to be in solution.
The first instants of photosynthesis
With this model researchers will be able to analyze light-absorbing processes and apply them to molecular
information processing devices. These will perhaps go beyond natural photosynthesis and enter realm of
technology.
Nowadays, scientists have been able to investigate and know much more about the energy producing steps
of photosynthesis than they do about the initial steps: the capture of light by arrays of light-absorbing
molecules of chlorophyll.
Chemist Jonathan Lindsey and his co-workers have built porphyrin pentamers and they have modified
them with carbohydrates appendages for increasing solubility. Other researchers had done a similar work
but they had obtained structures architecturally rigid and insoluble.
There have been reasons for this gap in knowledge: chlorophyll arrays are extremely complex and nobody
has been able to figure out their structure or find the relation between configuration and the light-capturing
function. So, researchers have had to turn to porphyrin molecules because they are closely related in
structure to chlorophyll and they are able to capture light.
a) Coloque las oraciones, párrafos, etc. en el orden correcto.
b) Marque los elementos vinculantes entre los diferentes segmentos del texto.
c) Traduzca el texto ordenado.
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Guía de Trabajos Prácticos - Inglés I - Cátedra de Inglés Técnico
Facultad de Bioquímica y Ciencias Biológicas - Universidad Nacional del Litoral
II)
Lea el fragmento siguiente:
In the study of proteins, a major aim has been to decipher their structure and to learn how they work. A
complete structural analysis is a laborious undertaking, and up to now biochemists have gained a thorough
understanding of only a small fraction of the known proteins. Nevertheless, some general principles have
emerged; researchers have now been able to recognize diverse proteins with the same substructures, and
these could probably have similar functions in many of them. The question about how the thousands of
proteins in a typical organism have evolved and diversified will also have to be answered. This is not
going to be a simple task, because the presence of shared substructures would imply a complex evolution,
where fragments of genetic information could have been exchanged and expressed in many proteins.
For the most part, proteins have always been able to work by selectively binding to molecules. In the case
of a structured protein, the binding often has to link identical molecules, but other proteins have to join to
molecules different from themselves. For example, receptor proteins will recognize messenger molecules
with a specific affinity for the receptor. Virtually, all the activities of proteins would be understood in
terms of such selective chemical binding but this is being governed by a dynamic equilibrium, where
molecules are allowed to bind or to be released, so at any instant the percentage of bound molecules will
have to depend on the relative amounts of the two substances and on the strength of the association
between them.
a) Marque aquellas oraciones a las que se hace referencia en el texto.
 Es de gran importancia conocer la estructura y funcionamiento de las proteínas.
 Existe una estrecha relación entre la estructura y la función de las proteínas.
 Las proteínas de un organismo típico han permanecido siempre en el mismo estado durante su
evolución.
 Cada una de las subunidades que componen una proteína están codificadas a nivel de genoma por
secuencias de información genética específicas.
 Las proteínas funcionan uniéndose en forma específica a otras moléculas.
 El reconocimiento proteína-molécula receptora se produce de acuerdo a las cantidades en que ellas
se encuentran en el medio.
b) ¿A qué se refieren THEIR, THEY, THESE y THEM, en el texto?
III)
a) Lea el texto y coloque los verbos marcados en tiempo perfecto o simple ( pasado o
presente), según corresponda:
Dendrimer supermolecules
Long ago nature (devise) exquisite strategies for manipulating the structures of the molecules necessary
for initiating and sustaining life. Chemists (try) for years to achieve such mastery over the structures they
create. Organic chemists (gain) substantial command over the synthesis of small complex molecules. But
the goal of constructing large well-defined molecules (be) more elusive.
The idea of directing molecular growth to make extremely large molecules with useful properties (derive)
from experiments done in the 1930s, when Prof. Staudinger (link) identical subunits, or monomers, into
strings of spaghetti-like molecules. About 10 years later, a second class of polymers formed by bridging
random-coil polymers at various sites (develop), giving rise to inflexible three-dimensional structures.
Today, Prof. D.Tomalia, who (develop) a new class of polymers in 1979, called dendrimers, says: “ I
(imagine) a system of molecular growth that resulted in large, symmetrical structures built in stages, much
as seasonal branching of young trees (lead) gradually to the development of a broad assembly of branches
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Guía de Trabajos Prácticos - Inglés I - Cátedra de Inglés Técnico
Facultad de Bioquímica y Ciencias Biológicas - Universidad Nacional del Litoral
in older trees”. This basic approach (result) in the creation of an entirely new class of polymer
architecture, in which concentric tiers of monomers are assembled around a single molecule at the center.
There is a good reason to believe that these synthetic constructions, capable of mimicking a variety of
biological structures including proteins, will prove valuable in medicine, the electronics industry and
biotechnology: researchers recently (find) evidence that dendrimers might one day be useful in gene
therapy, as vehicles for bridging DNA sequences into cells.
a) ¿Cuántos tipos de construcciones moleculares se han desarrollado, de acuerdo al texto?
Describa brevemente.
IV)
Complete con verbos en tiempo perfecto ( pasado, presente, futuro, continuo)
 Studies (show) that nitric oxide is perhaps one of the most important messenger molecules in living
organisms.
 Although Nobel (discover) nitroglycerin nearly a century before, not until the late 1970s was any insight
into the molecular mechanisms of this compound available.
 The results suggested that approximately 25 million U.S. civilians (infect) with HSV-2 by 1978.
 The World Health Organization has reported that by the year 2003, up to 90% of all HIV infections in
the world (transmit) heterosexually.
 Researchers (identify) many oncogenes during the last 10 years.
 The flow of information from nucleic acids to proteins, but not the reverse, (call) the central dogma of
molecular biology.
V)
Ponga los verbos que están entre paréntesis en Presente Perfecto o Pasado Perfecto (Voz
Activa o Pasiva), según corresponda.
Mode of communication of cholera
Cholera is a contagious disease and contaminated water is the most frequent source of infection. Other
forms of transmission (also, identify). Food that (irrigate) or (cook) with contaminated water
(repeatedly, implicate) as a cause of cholera. Foods that (show) the greatest potential to transmit the
disease include shellfish and seafoods, specially when they are eaten raw, fruits and vegetables grown in
soil that (fertilize) with human excrement or (irrigate) with raw sewage, and foods that (pack) in ice.
V.cholerae (also, find) on cooked grains such as rice and millet.
Most cases in the United States in recent years (be) food related. On March 30, 1991, for example,
crabmeat that (buy) in a fish market in Ecuador produced cholera symptoms in eight people that (eat) an
unrefrigerated salad.
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Guía de Trabajos Prácticos - Inglés I - Cátedra de Inglés Técnico
Facultad de Bioquímica y Ciencias Biológicas - Universidad Nacional del Litoral
VI)
Seleccione la traducción correcta de las siguientes oraciones (solamente UNA versión
es correcta.
a) The devastating effects of sexually transmitted diseases have been recognized for the last 500
years.
Los efectos devastadores de las enfermedades de transmisión sexual se reconocieron/ han sido
reconocidos/ habían sido reconocidos durante los últimos 500 años.
b) In patients with advanced ovarian cancer for whom traditional therapies had failed, 30%
responded to the drug.
De las pacientes con cáncer de ovario avanzado, en las que la terapia tradicional ha fallado/
falló/ había fallado, solamente el 30% respondió a la droga.
c) Industry has been producing huge amounts of waste in the last few years and we have been
trying to find a good method for its disposal.
La industria había estado produciendo/ estuvo produciendo/ha estado produciendo grandes
cantidades de desechos en los últimos años, y nosotros hemos estado tratando/ habremos
estado tratando/habremos tratado de encontrar un método de eliminación adecuado.
d) After oxygen combines with copper to form the oxide, there will be weight gain, and the red
metal will have changed to black cupric oxide.
Después que el oxígeno y el cobre se combinen para formar el óxido, habrá/habrá habido/
hubo aumento en el peso y el metal rojo se cambiará/ se cambiaría/ habrá cambiado a óxido de cobre
de color negro.
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Guía de Trabajos Prácticos - Inglés I - Cátedra de Inglés Técnico
Facultad de Bioquímica y Ciencias Biológicas - Universidad Nacional del Litoral
VII) Complete la siguiente tabla
COPY
INCLUDE
BREAK
Futuro Perfecto Continuo
Presente Perfecto Continuo
Futuro Simple (Voz Pasiva)
(he)
(we)
(I)
Forma “going to”
VII)
GRAM STAIN
A differential stain of great practical value for the identification of bacteria was discovered empirically in
1884 by Christian Gram, and it subsequently became known as the Gram stain. Many modifications exist,
but they all embody the following essential steps: a heat- fixed smear of cells is stained successively with
the basic dye, crystal violet, and with a dilute iodine solution. The preparation is then briefly treated
with an organic solvent (alcohol or acetone). Gram-positive bacteria resist decolorization and remain
stained a deep blue-black; Gram-negative bacteria are rapidly and completely decolorized. In performing
this staining procedure, it is essential to examine growing cells, for certain Gram-positive bacteria (for
example, Bacillus spp) rapidly lose the ability to retain the crystal violet-iodine complex after active
growth ceases. The outcome of the Gram reaction is thus to some extent conditioned by the
physiological state of the cell.
Yet many attempts to elucidate its mechanism have been made, the precise nature of the Gram
reaction, is not yet understood. The reaction is given only by intact cells; broken cells of a Gram-positive
bacterium are Gram-negative. The presence of the cell wall is essential , yet the dye complex is not
located in the wall itself. This can be shown by staining a Gram-positive bacterium and then stripping off
the cell wall by an appropriate enzymatic treatment in an isotonic medium. Under these conditions, the
enclosed protoplasts are liberated intact, and contain the dye complex. However , they are no longer
resistant to decolorization with alcohol; the attribute of Gram positiveness is lost upon removal of the
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Guía de Trabajos Prácticos - Inglés I - Cátedra de Inglés Técnico
Facultad de Bioquímica y Ciencias Biológicas - Universidad Nacional del Litoral
surrounding wall. This experiment suggests that the wall of a Gram-positive bacterium constitutes a
barrier to the extraction of the dye complex from the enclosed cell by organic solvents, but why this
should be so is still not known.
The widespread application of the Gram staining procedure to bacteria soon revealed that most readily
recognizable taxonomic subgroups among the bacteria are uniform with respect to their Gram reaction.
The evident taxonomic value of the Gram stain, accordingly, led to the proposal that it is correlated with
a basic chemical difference between Gram-positive and Gram-negative cells. Initially, attempts were
made to detect a substance in Gram-positive cells that both combines with and retains the crystal violetiodine complex, but no such cellular constituent has ever been demonstrated. The true chemical
significance of the Gram reaction only began to emerge about 20 years ago, when M. Salton developed
procedures for the isolation and chemical analysis of bacterial cell walls. Much subsequent work has
established that the outcome of the Gram reaction is systematically correlated with the major
differences both in the chemical composition and ultrastructure of procaryotic cell walls that have been
outlined above. The Gram reaction is, accordingly, an empirical staining method that is easy to apply and
that distinguishes, although not always with complete reliability, two major subgroups of procaryotes
that differ with respect to the nature of the cell wall. Unfortunately, the differentiation of these two
subgroups by other and more reliable methods is not easy: it requires either electron microscopic
examination of wall structure in thin sections of cells or chemical detection of the group-specific
polymers. We shall designate these two large subgroups as Gram-positive bacteria and Gram-negative
bacteria –for no other simple group designations are in common use, while we recognize that the Gram
staining procedure is not always a wholly reliable method to differentiate between them. In fact, the
limitations of the staining procedure occur almost entirely in the context of the Gram-positive group:
some bacteria, clearly assignable to this group by virtue of wall structure and composition may give a
Gram-negative or Gram-variable staining reaction.
a) Complete el siguiente diagrama con información proveniente del texto.
Smear
of cells
Gram(+) Gram(-)
b) Complete las siguientes oraciones:
a) El elemento determinante en la retención del colorante en el interior de las células es.......................
b) Para poder estudiar los efectos de esta coloración, las células deben estar.....................y...................
c) Las principales limitaciones de este método se relacionan con las bacterias...........................,
porque.......................................
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Guía de Trabajos Prácticos - Inglés I - Cátedra de Inglés Técnico
Facultad de Bioquímica y Ciencias Biológicas - Universidad Nacional del Litoral
IX) HYPERLIPIDAEMIA ADVANCES AND RETREATS
Both hyperlipidaemia and raised serum cholesterol concentrations are usually suggested as important
correlates of ischaemic heart disease. This has led to repeated attempts to lower serum lipid
concentrations and so to prevent the disease. Evidence from both North America and Finland suggests that
changes in life style, such as stopping smoking and altering diet, might be beneficial, but the simultaneous
changes in the prevalence of the disease make the interpretation of the individual roles of such factors
difficult. In a different category are the few patients with severe and genetic hyperlipidaemias, for their
health is seriously impaired and so a vigorous treatment is required.
Since the protective role of HDL was rediscovered, the diets and drugs that have been extensively used
in hyperlipidemia have been examined for determining their effects on it. Many presentations at symposia
showed that serum concentrations of HDL rise somewhat after treatment with both bile-acid binding
resins and the clofibrate and nicotinic acid groups of drugs. In contrast, neomycin and probucol definitely
reduced HDL. The effect of dietary polinsaturated fats remains contentious.
Clofibrate,and to a lesser extent, nicotinic acid induce oversaturation of bile with cholesterol and cause
gall stones: analogues of these drugs might carry a lesser risk, but that remains only a speculation.
Analysis of bile had already shown that cholestyramine and probucol should be free of this problem and
chenodeoxycholic acid should actually protect against gall stones and reduce hypertriglyceridemia.
With respect to dietary modifications and drugs, three deserve particular attention. L-Carnitine is a
dietary constituent and is non-toxic: it has been given as a supplement, for it is thought that part of the
disorder in hyperlipidaemia is the result of deficiency of L-Carnitine, and some biochemical improvement
has been observed. Compactin is another product of an exhaustive Japanese review of microbial products
to find an inhibitor of liver and intestinal cholesterol syntheses. Not only is it extremely potent but it is
also effective in a dose of 15-30 mg daily in hypercholesterolemia. Efficacy, safety and clinical usefulness
have been tested. Probucol has recently been introduced into Britain and it has been available in the
United States for three years. It is palatable and moderately hypocholesterolaemic, but the fact that it
lowers HDL may limit its usefulness.
What does this means for the physician? Clearly there is neither place for indiscriminate prophylactic
drug treatment in the general community, nor enough health education that should focus not only on
cigarette smoking but prudent diet and screening for hypertension as well. For the individual with either a
poor story -personal or familiar-, or with appreciable hyperlipidaemia, treatment should invariably be
supervised from a specialist clinic and so some of the mistakes of the past will be avoided.
1) ¿A qué se refieren las palabras que están en negrita?
2) Marque todos los conectores que reconozca. Diga qué elementos están uniendo.
3) Extraiga la idea principal de cada párrafo (no más de dos o tres líneas) y construya con ellas un
resumen del texto.
4) ¿Cuántas categorías de pacientes se consideran?
5) ¿Qué ventajas y desventajas presentan las drogas del grupo de los clofibratos y el ácido
nicotínico?
6) L-Carnitina, Compactina, Probucol: haga un esquema que resuma las ventajas y desventajas de
estos compuestos.
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Guía de Trabajos Prácticos - Inglés I - Cátedra de Inglés Técnico
Facultad de Bioquímica y Ciencias Biológicas - Universidad Nacional del Litoral
X) THE NITROGEN CYCLE
Yet molecular nitrogen is abundant and constitutes about 80% of the earth’s atmosphere, it is
chemically inert and therefore not a suitable source of the element for most living forms. For this reason,
the cyclic transformation of nitrogenous compounds is of paramount importance in supplying required
forms of nitrogen to the various nutritional classes of organisms in the biosphere and the process of
nitrogen fixation is a limiting step.
Biological nitrogen fixation in nature is mediated by both free-living bacteria (nonsymbiotic nitrogen
fixation) and bacteria which exist in mutualistic partnership with plants (symbiotic nitrogen fixation). The
most important agents of symbiotic nitrogen fixation are the bacteria of the genus Rhizobium, which
invade the root hairs of leguminous plants and develop in nodules where the nitrogen fixation occurs.
The most important agents of nonsymbiotic nitrogen fixation are blue-green bacteria, but there are
other bacteria (both aerobic and anaerobic species) which are also able to fix nitrogen and ought not to
be underestimated.
Algae and plants assimilate nitrogen either as nitrate or ammonia. Nitrate is the form in which
nitrogen is assimilated, but it must be reduced in the cell to ammonia. This process proceeds only to the
extent to which nitrogen is required for growth, and ammonia is not excreted. This feature in particular
distinguishes nitrate assimilation by plants and microorganisms from nitrate reduction, a process of
anaerobic respiration which is limited to procaryotes.
Unlike plants, however, animals do excrete a significant quantity of nitrogenous compounds and the
form in which this nitrogen is excreted varies from one group of animals to another. When an animal or
plant dies, its body constituents will be immediately attacked by microorganisms and the nitrogenous
compounds will be decomposed with the liberation of ammonia. Part of the nitrogen is assimilated by
the microorganisms and thus converted into microbial cell constituents. These are converted to
ammonia after the death of the microorganisms themselves (ammonification).
The conversion of ammonia to nitrate (nitrification) will be brought about by two highly specialized
groups of bacteria. In the first step ammonia will be oxidized to nitrite and then this will be oxidized to
nitrate. Nitrates have played and important role not only in the development of agriculture but also in
the destructive activities of man, for gunpowder -the only explosive which was used for war before the
invention of nytroglycerine- is a mixture of sulfur, carbon and saltpeter (KNO3 ).
In anaerobic conditions, there are many bacteria that can use nitrate in place of oxygen as a final
hydrogen acceptor, and so when organic matter is decomposed in soil or water and oxygen is exhausted
as a result of aerobic microbial respiration, certain of these aerobes will continue to respire the organic
matter with the help of nitrates. As a consequence, nitrate is reduced. Some bacteria are only able to
reduce nitrate to the level of nitrite but others are able to reduce it to nitrogen gas. By this latter process
(called denitrification), combined nitrogen is removed from soil and water and N2 gas is released to the
atmosphere.
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Guía de Trabajos Prácticos - Inglés I - Cátedra de Inglés Técnico
Facultad de Bioquímica y Ciencias Biológicas - Universidad Nacional del Litoral
CON INFORMACIÓN PROVENIENTE DEL TEXTO, ELABORE UN ESUQEMA QUE RESUMA EL
CICLO DEL NITRÓGENO EN LA NATURALEZA.
XI) Con información de este texto complete la tabla que está a continuación
TARGETS FOR CERTAIN ANTIBIOTIC AGENTS IN PROCARYOTIC AND EUCARYOTIC CELLS
The penicillins and several other classes of antibiotics are selectively toxic for procaryotes, for they are
able to affect steps in the synthesis of the peptidoglycan component of the cell wall, which is a molecular
component essential for the stability of the cell in most procaryotes, yet it is not synthesized by
eucaryotes. The only procaryotes which are insensitive to these classes of antibiotics are the
Mycoplasma group, in which the cell wall is absent, and the halophilic bacteria which lack the
peptidoglycan component of cell walls.
The polyene antibiotics (e.g., nystatin, filipin and amphotericin B) are bound to sterols in the cell
membrane of sensitive organisms and result in destruction or malfunction of the membrane and the
leakage of essential metabolites out of the cell. A high sterol content is characteristic of the eucaryotic
cell membrane, but not of the membranes of most procaryotes. The polyene antibiotics are accordingly
agents of selective toxicity for eucaryotic cells, and the only procaryotes which are affected by polyene
antibiotics are members of the Mycoplasma group, which incorporate exogenous sterols into their
membranes.
A very large number of antibiotics interfere with steps in protein synthesis and many specifically
inhibit the function either of 70S ribosomes (characteristic of procaryotes) or 80S ribosomes
(characteristic of eucaryotes). The glutarimides (e.g., cycloheximide) specifically inhibit protein synthesis
of the 80S ribosome, and are therefore selectively toxic for eucaryotes. The aminoglycosides are able to
specifically inhibit protein synthesis on the 70S ribosome. These antibiotics are thus selectively toxic for
procaryotes. However, eucaryotic organellar protein synthesis may also be affected, for the ribosomes of
chloroplasts and mitochondria are functionally similar to procaryotic ribosomes. The antibiotic
concentrations which are required to affect significantly the activities of mitochondria or chloroplasts
are, however, considerably higher than those which are necessary to inhibit bacterial growth, probably
because the outer membranes of these organelles interpose a partial permeability barrier.
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Facultad de Bioquímica y Ciencias Biológicas - Universidad Nacional del Litoral
Classes of antibiotics which act on targets specific to either procaryotic or eucaryotic cells
ACTIVE AGAINST
ANTIBIOTICS
MODE OF ACTION
PROCARYOTES
EUCARYOTES
+a
-
-b
+
-
+
+
-c
a
Except those (Mycoplasma group)
b
Some mycoplasmas that incorporate sterols from the growth medium into the membrane are
sensitive.
c
At high concentrations they may affect organellar protein synthesis.
XII) Traduzca este texto
THE DIFFERENCES BETWEEN PROCARYOTES AND EUCARYOTES
The numerous and profound divergences with respect both to organization and to function between
eucaryotic and procaryotic cells have been revealed gradually and have been fully recognized only
recently. It is now evident that many universal cellular functions are mediated in markedly different ways
by the two kinds of cells. This fact has raised some major evolutionary questions which notably concern
the primary origins and relationships between the two kinds of cells. On the other hand, the apparent
resemblances between procaryotes and two classes of eucaryotic organelles, chloroplasts and
mitochondria, with respect to the structure of the genetic material and the machinery of transcription
and translation, suggest a fascinating evolutionary possibility which has been much discussed: namely
that chloroplasts and mitochondria had evolutionary origins distinct from those of the other component
parts of the eucaryotic cell. These two classes of organelles might have been derived from free-living
procaryotes which would have been endowed respectively with respiratory and photosynthetic function,
and would have then entered into an endosymbiotic relationship with primitive eucaryotes. Perhaps
they gradually became not only closely integrated with the machinery of the host cell but ultimately lost
part of their genetic autonomy and became incapable of independent existence.
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Facultad de Bioquímica y Ciencias Biológicas - Universidad Nacional del Litoral
XIII)
INFECTIONS OF THE SUBEPITHELIAL TISSUES: The phagocytic cells and the
inflammation process
Phagocytic cells are found both in the circulatory system and in the tissues. The white blood cells include
two actively phagocytic types: monocytes and granulocytes. Granulocytes owe their name to the
presence of granules in their cytoplasm. All of them are capable of phagocytosis but only in the
neutrophils is phagocytosis sufficiently active to play a significant role in host defense.
When tissue infection occurs, both neutrophils and monocytes are attracted to the site of the injury by
chemotactic substances. During this process, the monocytes enlarge and develop into cells with
enhanced phagocytic activity (macrophages). These also occur as fixed cells in certain organs: the liver,
spleen, bone marrow and lymph nodes. The fixed macrophages are collectively known as the
reticuloendothelial system, for they are either forming a supporting network or lining the sinuses in
these organs.
When a tissue of a higher animal is subjected to any of a variety of irritations, it becomes “inflamed”. The
characteristics of inflammation -reddening, swelling, heat, pain- are familiar. Yet the causes of the heat
and pain are not well understood, the reddening and swelling are readily explained. In the area of
inflammation the blood capillaries are dilated, so the flow of blood through the area is increased. The
walls of the capillaries also become more porous, so soluble proteins escape from the vessels and cause
an osmotic movement into the tissues.
Inflammation is produced by widely different irritants. This suggests that the symptoms are caused by a
substance which has been released from the damaged cells or activated in the body fluids. Among the
many different compounds that have been extracted from cells or serum and shown experimentally to
produce inflammation, the most thoroughly studied are histamine and serotonin. Both histamine and
serotonin are present not only in blood platelets but also in the cells of many tissues, and are released in
response to a variety of stimuli.
EN EL TEXTO ANTERIOR:
a) marque todos los coordinantes que encuentre (ya los hemos señalado en las primeras líneas).
b) marque también CLARAMENTE qué elementos está uniendo cada uno.
XIV)
THE PHYSIOLOGICAL ROLE OF VITAMINS
Since 1912, vitamins have been identified as organic compounds of relatively simple structure. They
are required in small amounts, for they are neither utilized as sources of energy nor required as a source of
aminoacid nitrogen.
When ascorbic acid (vitamin C) is administered to normal human subjects, a relatively large proportion of
the test dose will normally be found in urine and a delay in the excretion of ascorbic acid will be taken as
an indication of vitamin C deficiency (scurvy). The characteristic lesions of this disease include not only
petequial haemorraghes in the skin and mucous membranes but also degenerative changes in the cartilage
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and bone matrices.
A deficiency in thiamine -essential in the diet of all higher animals- will generally lead first to loss of
appetite and nausea, and then to both neurological symptoms and cardiac manifestations (these may result
in death due to cardiac hypertrophy). On the other hand, the close relation between thiamine and
carbohydrate metabolism has been indicated by the observation that rats are able to survive many months
without dietary thiamine when they are allowed to feed on a diet with no carbohydrates.
Pellagra, the human disease which is caused by nicotinic acid-deficient diets, is characterized mainly
by dermatitis, diarrhea and dementia (this could be the result of an impaired ability of the brain tissue to
metabolize carbohydrates. However, nervous lesions might be seen in pellagra, but these could be caused
by deficiencies of other factors such as thiamine, for human diets that lead to pellagra are deficient not
only in nicotinic acid but also in other members of the B complex.
As regards folic acid, the development of anemia would be the most obvious pathological defect in
experimentally indicted folic acid deficiencies, for it is evident that derivatives of folic acid play an
important role in the formation of normal erythrocytes.
The fat-soluble vitamin A has been related to the visual process in animals and this is the reason why
the onset of a vitamin A deficiency can most readily be detected by tests for dark adaptation. It should be
added, however, that vitamin A has been implicated as the key substance not only in the visual response in
dim light but also in colour vision. It is toxic to animals when it is taken in large doses over a long period
of time.
A PARTIR DE LA SIGUIENTE TABLA, CONSTRUYA ORACIONES QUE REFLEJEN LA
INFORMACIÓN PROPORCIONADA POR EL TEXTO.
a) An excessive intake of vit. A produces ...................................................
b) Folic acid deficiency causes ...................................................................
c) Thiamin deficiency results in .................................................................
d) Shortage of niacin produces ...................................................................
e) Prolonged vit. C deficiency leads to ........................................................
f) Vitamin A deficiency can lead to ............................................................
1- malformation of erythrocytes.
2- scurvy.
3- symptoms of toxicity.
4- blindness.
5- inflammation of the skin.
6- disorders of carbohydrate metabolism.
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XV) “HEAT STERILIZATION”
1) Lea los títulos. Basándose en ellos, ¿qué vocabulario esperamos encontrar?
Anote por lo menos 10 palabras.
2) ¿Qué tipo de información esperamos encontrar en la introducción?
3) Sin usar el diccionario, veamos si podemos hacer un resumen solamente con las palabras parecidas
al Castellano o conocidas.
4) De lo que desconozco, ¿qué necesito para completar el resumen? Delimitamos claramente lo que
no se comprende y de eso eliminamos lo que nos parece que no es fundamental.
5) ¿Qué clase de información podríamos encontrar en 1.1 y 1.2? (definiciones, clasificaciones,
descripciones físicas, funcionales o procesuales, clasificaciones, ejemplificaciones, etc.)
6) Verificamos nuestras predicciones leyendo rápidamente y usando pistas léxicas (palabras que se
repiten, sinónimos, prefijos y sufijos), gramaticales, palabras marcadoras del discurso (conectores,
indicadores de secuencia, etc.).
7) Diga si estos enunciados son verdaderos o falsos:
a) Different heat sterilization techniques serve the same sterilization purposes.
b) The temperature at which the irreversible denaturation of proteins is achieved is always the
same.
c) Sterilization processes which use dry heat affect the cell constituents through oxidative
mechanisms.
d) Dry-heat sterilization methods are slower than those which use moist heat.
8) Conteste las siguientes preguntas:
a)
b)
c)
d)
e)
¿Cuáles son las variables que afectan el tiempo necesario para destruir un microorganismo?
¿Hay diferencias de resistencia entre las células vegetativas y los esporos?
Dentro de los esporos, ¿qué es lo que determina la mayor o menor resistencia al calor?
En el párrafo 8: ¿a qué se refiere el autor con la expresión “differences in exposure conditions”?
Clasifique los agentes infecciosos mencionados en el último párrafo de acuerdo con su
resistencia al calor.
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XVI)
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XVII) The Procaryotes: An Introductory Survey
The range of cell size in procaryotes
Both among protists and among procaryotes, the dimensions of the cell cover a substantial range. The
largest unicellular bacteria are considerably larger than the smallest unicellular protists, so cell size should
not be used as an absolute character to distinguish between the members of these two great microbial
assemblages.
Nevertheless, the average cell size of procaryotes would be considerably less than that of protists, and the
smallest bacteria could have cells far below the lower limit of cell size in eucaryotic groups. Some
bacteria do have cells only just resolvable with the light microscope and they may overlap in size with the
larger viruses. This great variation in size allows us to propose cellular volume as the only satisfactory
basis on which cell size can be defined.
In principle, the lower size for a procaryotic cell has been set by molecular limitations. To reproduce
itself, any cell has to resort to a large number of different enzymes. Nucleic acids, lipids and
carbohydrates must also be present.
Several factors are probably operating to keep procaryotic cells small. In the first place, it is a general
biological rule that the lower the size of the organism, the higher the rate of metabolism. Small size is an
essential condition for rapid growth, for the growth rate is primarily determined by the overall rate of
metabolism. Many bacteria are characterized by extraordinarily rapid growth, with doubling times of less
than an hour under optimal conditions. Such growth rates could be far higher than those of most protists.
This property undoubtedly confers a decisive biological advantage in many situations where bacteria have
to compete for nutrients with protists, and it is probably the most important single factor in the survival of
many bacteria in nature.
A second factor can be surmised from the properties of very large bacteria. These lack adaptive flexibility
and cannot readily accommodate to minor changes in the environment. The upper size limit for the
procaryotic cell might be determined by the difficulty of maintaining a satisfactory regulation and
coordination of metabolic activity in a large cell.
En base a la información proporcionada por el texto:
1) Indique en pocas palabras, y CLARAMENTE de qué se trata el texto.
2) Diga cuántos grupos de organismos se comparan y cómo se llaman.
3) Determine si las siguientes afirmaciones son verdaderas o falsas.
 El tamaño es una característica que permite diferenciar con claridad a los miembros de los
diferentes grupos.
 Algunos virus y bacterias pueden tener el mismo tamaño.
 El volumen celular es un dato adecuado para definir el tamaño celular.
 Existe una relación directa entre la velocidad del metabolismo y el tamaño del
organismo.
 Los procariotas presentan ventajas de supervivencia frente a los protistas.
4) Para cada enunciado, elija la opción que le parezca más apropiada.
la estructura
 El tamaño de una célula procariota está limitado por el contenido molecular
la cantidad de enzimas
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más rápidamente
 Si un organismo es pequeño, crece más lentamente que uno grande
a igual velocidad
cada hora
 Hay muchas bacterias que pueden duplicar su cantidad cada dos horas
en menos de una hora
tienen
 Las células de mayor tamaño no tienen
dificultades para adaptarse al medio ambiente.
podrían tener
XVIII) Pioneering work on pure culture techniques
Around 1870 O. Brefeld, a great mycologist, had introduced the practice of both isolating single cells and
cultivating fungi on solid media. Yet his methods of obtaining pure cultures had worked admirably for the
fungi, they were unsuitable for cultivating the smaller bacteria, and so other methods had to be devised.
A promising approach had already been suggested by the earlier observations of J. Schroeter, for he had
been able to obtain isolated bacterial growths, or colonies, on such solid substrates as potato, starch and
bread. The colonies differed from one another, yet within each colony the bacteria were of one type.
The mycrobiologist Robert Koch first experimented with potato cuts, which he placed in sterile, covered
glass vessels and then inoculated with bacteria. However, potatoes have some disadvantages, for the cut
surface is moist and so motile bacteria spread freely over it. Koch perceived that it would be far better to
solidify a well-tried liquid medium with some clear substance, so a translucent gel could be prepared and
the developing bacterial colonies would be clearly visible. At the same time, the differing nutritional
requirements of different bacteria could be met by modifying the composition of the liquid base.
With this in mind, he added gelatin as a hardening agent and the gelatin surface was then seeded by
picking up a minute quantity of cells (the inoculum) on a platinum needle, and drawing it several times
rapidly and lightly across the surface of the jelly. This became known as the streak method for isolating
bacteria. The pure cultures were transferred to tubes with sterile nutrient gelatin that had been plugged
with cotton wool and set in a slanted position. Such cultures became known as slant cultures. Shortly
thereafter, Koch discovered that he could mix the bacteria with the melted gelatin, so the bacteria could
become immobilized in the set jelly and develop into isolated colonies. This became known as the pour
plate method for isolating bacteria.
a) Traduzca el texto completo.
b) Con la idea principal de cada párrafo construya un breve resumen (verifique que las ideas estén
CLARAMENTE expresadas.
c) Diga si los siguientes enunciados son verdaderos o falsos (corrija los falsos):
a) Brefeld había obtenido buenos resultados en el aislamiento de bacterias.
b) Las colonias son grupos de células bacterianas de diferentes clases
c) El agregado de un agente solidificante mejoró el procedimiento de aislamiento de
bacterias.
d) Los nutrientes del medio de cultivo pueden ser modificados.
e) En el pour plate method las bacterias se desarrollan en la superficie del medio.
d) Responda las siguientes preguntas:
a) ¿Por qué los potato cuts no resultaban adecuados para el aislamiento de bacterias?
b) ¿Cuál era el objetivo de agregar una sustancia solidificante a los medios líquidos?
c) ¿Qué es un inoculum?
d) ¿Qué métodos de cultivo en medio sólido se mencionan y en qué consiste cada uno?
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