Download Examen parcial inglés II

1º parcial Inglés II
1) EFFECT OF TEMPERATURE ON MICROBIAL GROWTH
 Factors determining temperature limits for growth
The numerical values of cardinal temperatures (those at which microorganism
growth is minimal, optimal and maximal) and the range of temperatures over which
growth is possible, vary widely among bacteria. Some which have been isolated from
hot springs are able to grow at temperatures as high as 95ºC, while others, isolated
from cold environments, can grow at temperatures as low as -10ºC. On the basis of the
temperature range of growth, bacteria are frequently divided into three broad groups:
termophiles, which grow at elevated temperature (above 55ºC); mesophiles, which grow
well in the midrange of temperature (20 to 45ºC); and psychrophiles, which grow well
at 0ºC.This tripartite classification of temperature response does not take fully into
account the variation among bacteria with respect to the extent of the temperature range
over which growth is possible.
Represente gráficamente la información brindada por este texto, de manera que se
vea claramente la relación entre los grupos de bacterias y sus rangos
correspondientes de temperatura.
 The factors determining the temperature limits for growth have been revealed by both
comparisons of the properties of organisms with widely different temperature ranges
and analyses of the properties of temperature-sensitive mutants, the temperature range
of which has been decreased by a single mutational change.
Studies on the kinetics of thermal denaturation of not only enzymes but also cell
structures containing proteins (e.g., flagella, ribosomes) have shown that many specific
proteins of thermophilic bacteria are considerably more heat stable than their
homologues from mesophilic bacteria. It is also possible to make an approximate
determination of the overall thermal stability of soluble cell proteins by measuring the
rates at which the protein in a cell-free bacterial extract becomes insoluble as a result of
heat denaturation at several different temperatures. It can be clearly demonstrated that
virtually all the proteins of a thermophilic bacterium remain in the native state after a
heat treatment, this denaturing virtually all the proteins of a related mesophile. It
therefore follows that the adaptation of a thermophilic microorganism to its thermal
environment can be achieved only through mutational changes, which are able to affect
the primary structures of most cell proteins.
Although the evolutionary adaptations which have produced thermophiles must have
involved mutations that increased the thermal stability of their proteins, most of the
mutations affecting the primary structure of a specific protein decrease the thermal
stability of that protein, even though many of these mutations could have little or no
effect on its catalytic proteins. Consequently, in the absence of counterselection by a
thermal challenge, the maximal temperature for growth of any microorganism should
decline progressively as a result of random mutations that affect the primary structure of
its proteins. This inference is supported by the observation that psychrophilic bacteria
isolated from antarctic waters contain a large number of exceptionally heat-labile
proteins.
Diga si las siguientes afirmaciones son verdaderas o falsas (marque los segmentos
de texto donde ha encontrado su respuesta)
a) Las proteínas de las bacterias mesófilas son más resistentes al calor que las de las
termófilas.
b) Las proteínas que han sido objeto de mutaciones generalmente muestran mayor
estabilidad al calor.
c) Lo más común, es que después de varias mutaciones la temperatura máxima de un
microorganismo disminuya.
d) Las proteínas de las bacterias halladas en lugares fríos son muy sensibles al calor.
e) Podemos decir que la mayor o menor estabilidad al calor de las proteínas es lo que
determina la supervivencia de un microorganismo a diferentes temperaturas.
2) HAZARDS FROM CHEMICAL AND RADIOACTIVE POLLUTION IN
WATER
When present above a certain level and ingested in water, some chemical
pollutants (e.g., nitrates, arsenic and lead) may constitute a direct toxic hazard, not
posed by other water constituents, such as fluorides, which are beneficial, and may be
essential to health in small concentrations ( although toxic when taken in larger
amounts. Certain other substances or chemical characteristics may affect the
acceptability of water for drinking purposes, including substances causing odours or
tastes, acidity or alkalinity, anionic detergents and naturally occurring salts of
magnesium and iron. Both international and national criteria and standards have been
established, so that a basis for the control of human exposure to many of these
substances through ingestion of polluted water can be provided.
Ingestion is, however, only one possible pathway to exposure, since man can
be exposed to water pollutants through other types of direct contact that would include
recreation or the use of water for personal hygiene. The possible health implications
these non-drinking uses of water (including agricultural and industrial uses) would pose
are less well understood, no international criteria or guidelines (based on the actual
intake of drinking water and the body burden resulting from other sources) existing for
the control of such exposure.
Since chemical water pollutants –at the level now existing in water bodiesmay influence man´s health indirectly by disturbing the aquatic ecosystems or by
accumulating in aquatic organisms used in human food, it would be advisable to analyse
public health aspects of water pollution related to substances such as compounds of
toxic metals and organochlorine pesticides.
The various chemical and biochemical transformations that pollutants may
undergo in the aquatic environment also deserve attention, as chemical change may
affect their biological availability or toxicity, which may be either enhanced or reduced.
Although essential to the understanding of the health implications of chemical water
pollution, these physical, chemical and biological processes and their mechanisms have
not been completely understood.
1) Haga la traducción de este texto
2) Elabore un resumen del mismo
3) Responda las siguientes preguntas:
a) ¿De qué formas puede el ser humano entrar en contacto con sustancias
contaminantes provenientes del agua?
b) Mencione algunos tipos de sustancia que suelen contaminar el agua.
c) ¿Qué efectos pueden producir algunos de ellos en el agua?
d) ¿Qué aspectos deberían tenerse en cuenta si se elaboraran normas internacionales
para regular la exposición a contaminantes a través del agua?
e) ¿Qué tipo de transformaciones pueden sufrir los contaminantes en el agua y cuáles
aspectos de estos compuestos pueden ser afectados?
3) COLIFORM BACTERIA IN SANITARY ANALYSIS
For years, it has been known that the enteric diseases caused by the coliform bacteria
are transmitted almost exclusively by the faecal contamination of water and food
materials. Contaminated water supplies are by far the most serious source of infection,
being responsible for the massive epidemics of the more serious enteric diseases
(particularly typhoid fever and cholera) that periodically scourged all countries until the
beginning of the XX century. Today these diseases are almost unknown in the Western
world, although cholera has recently reappeared in the countries bordering the
Mediterranean. Their eradication was achieved primarily by appropriate sanitary
controls, an essential part of this operation being the development of bacteriological
methods ascertaining the occurrence of faecal contamination in water and foodstuffs.
As they are usually present in small numbers, it is seldom possible to isolate
enteric pathogens directly from contaminated water. To demonstrate the fact of faecal
contamination, it is sufficient to show the sample under examination contains bacteria,
which are specific inhabitants of the intestinal tract, even though they may not be agents
of disease. Although the bacteria normally used as indices of such contamination are the
faecal streptococci and E. coli, the methods of sanitary analysis developed by
bacteriologists differ somewhat from country to country.
When trying to detect E. coli, lab workers first inoculate dilutions of the sample
into tubes containing lactose broth, which are then incubated at 37ºC and examined after
1 or 2 days. Cultures showing acid and gas formation are then streaked on a special
medium. One of the media most commonly used is a lactose-peptone agar containing
two dyes, eosin and methylene blue (EMB agar). On this medium, E. coli produces
blue-black colonies with a metallic sheen, whereas the other principal member of the
group capable of fermenting lactose with acid and gas production, Enterobacter
aerogenes (not necessarily indicative of faecal contamination) produces pale pink
mucoid colonies without a sheen.
1) Traduzca el texto
2) Complete estas oraciones con información proveniente del texto
a) Las enfermedades de las que se habla son transmitidas principalmente transmitidas
por …………………. Y ……………………
b) De las dos enfermedades que se mencionan, la que aún prevalece es ……………..
especialmente en la región ……………………..
c) El hallazgo de abcterias intestinales (normalmente, ……………… y …………… )
es un índice de ……………………………
d) El EMB se usa para diferenciar …………………………. De ………………….
e) En el medio con lactosa y agar, uno de los microorganismos produce colonias
……………….. mientras que el otro …………………………..
3) Diga si estas oraciones son verdaderas o falsas.
a) Se determina que la muestra está contaminada solamente si la bacteria aislada es
patógena.
b) Existe un consenso mundial con respecto a la metodología utilizada.
c) La muestra no se inocula directamente en el caldo con lactosa.
d) El EMB es un medio líquido.
e) No todos los organismos productores de ácido y gas son índice de contaminación.
4) THE PRODUCTION OF ANTIBIOTICS
Antibiotics were the first industrially produced microbial metabolites that were
not major metabolic end products, for the yields –which had to be calculated in terms of
conversion of the major carbon source into antibiotic- are low and are greatly influenced
by both the composition of the medium and the other cultural conditions.
The wild type strain of Penicillum chrysogenum, which had been first used for
penicillin production, yielded approximately 0.1 gram of penicillin per liter, so a mutant
was selected which produced 8 grams per liter under the same growth conditions.
Subsequent strain selection by means of chemical mutagenesis has led to the
development of new strains with which even greater production capacity has been
achieved, and so by such sequential genetic selection for antibiotic production,
improvements of antibiotic yield as great as a thousandfold have often been obtained.
Yet most genetic improvement has been empirical and large numbers of
mutagenized clones are evaluated for their abilities to produce large quantities of the
antibiotic, with increase knowledge of the pathways of biosynthesis of antibiotics more
rational approaches are being exploited. It is now possible to select strains in which
control of the synthesis of known precursors of an antibiotic has been altered by
mutations, so such strains will be able to produce large amounts of not only the
precursor but also the antibiotic end product.
The synthesis of antibiotics begins only when growth of the microorganisms that
produce them has virtually ceased, for they belong to a class of microbial products
whose synthesis is not associated with growth and which have been called secondary
metabolites. The control mechanisms that trigger the synthesis of secondary metabolites
when growth ceases are a fascinating but almost completely unexplored aspect of
biochemical regulation.
Yet the microorganisms which are used to produce antibiotics are all aerobes
and are grown under conditions of vigorous aeration, the production process is generally
referred to in the technical literature as “fermentation”. Antibiotics are produced by socalled submerged cultivation methods by means of deep stainless steel tanks that will
have to be subjected to both continuous forced aeration and rapid mechanical agitation.
Not only is the provision of adequate aeration of great importance to yield, but the
energy which has to be expended for aeration contributes appreciably to the cost of
production.
1) Decida cuál de las curvas representa el desarrollo del P. chrysogenum y cuál la
producción de penicilina, y subraye la o las pàrtes del texto que le
proporcionan esa información
2º Parcial - Inglés II
1) RABIES AND MONOCLONAL ANTIBODIES
Rabies, a human disease which is known to be transmitted by animal
bite and for which man serves as accidental host, has been responsible in the
past for serious epidemics that have radically altered the course of human
history. By either eliminating or controlling both vectors and reservoirs of
infection (the species from which the vector derives the infection) man has
been able to eradicate this and other diseases from large areas.
Although two researchers, G. Zinke and G. Breschet, had already
demonstrated that rabies was an infectious disease, it was not until modern
techniques utilizing the electron microscope and tissue culture began to be
employed about 30 years ago that the viral agent could be characterized.
Taxonomically it belongs to the rhabdoviruses, a large group of viral agents
affecting plants, insects and both warm-blooded and cold-blooded animals.
Not so many years ago, some researchers became aware of the
impossibility of studying how these virus had interrrelated and evolved, unless
reagents able to identify the specific antigenic determinants of the various
components of the rhabdoviruses were developed. Now, however, the
availability of monoclonal antibodies, particularly those detecting antigenic
determinants of the nucleocapsids of viruses belonging to the rabids group may
allow the interrelations among various rhabdoviruses to be studied.
Until recently, the antigens represented by glycoproteins and
nucleocapsid proteins were thought to be similar, if not identical, regardless of
the strain of rabies virus from which they could be isolated in relatively pure
form. When studying virus preparations with rabies-specific monoclonal
antibodies, however, researchers found that strains of rabies virus formerly
considered as being identical or very closely related could be quite different
antigenically. For example, two fixed laboratory-adapted virus strains derived
from the rabies virus originally isolated by Louis Pasteur differed antigenically
both from the Pasteur virus and from each other.
Monoclonal antibodies can potentially be produced relatively cheaply
and in large quantities. Since they react more specifically than antibodies used
for diagnosing rabies, they should replace animal sera for such purposes. In
addition, they should replace antirabies gamma globulin of human origin -this
being expensive and difficult to obtain- in the postexposure treatment of people
bitten by rabid animals.
1) Traduzca el texto
2) Diga si estas afirmaciones son verdaderas o falsas y corrija las falsas.
 En esta enfermedad, el hombre actúa como vector y reservorio de la
enfermedad.
 A principios del siglo XX todavía no se habían determinado todas las
características del virus de la rabia.
 Los anticuerpos monoclonales son altamente específicos.
 El grupo de los rabdovirus afecta específicamente al hombre y otros
mamíferos.
 Se pudo detectar que distintas cepas del virus tienen características
antigénicas diferentes.
3) Responda estas preguntas:
*
¿Cómo ha logrado el hombre el control de esta enfermedad?
*
¿En qué se basaban las técnicas que se desarrollaron para caracterizar al
virus?
*
¿Por qué anteriormente no se podían conocer las características evolutivas
de estos virus, o cómo se
relacionaban entre sí?
*
¿Qué componentes del virus son especialmente útiles en la generación de
anticuerpos monoclonales?
*
¿Qué ventajas presentan estos anticuerpos?
2) SEPARATION AND PURIFICATION TECHNIQUES
2.2. Recrystallization
Crystallization is the deposition of crystals from a solution or melt of a given material.
During the process of crystal formation, a molecule will tend to become attached to a growing
crystal composed of the same type of molecules because of a better fit in a crystal lattice for
molecules of the same structure than for other molecules. If the crystallisation process is
allowed to occur under near-equilibrium conditions, the preference of molecules to deposit on
surfaces composed of like molecules will lead to an increase in the purity of the crystalline
material. Thus the process of recrystallisation is one of the most important methods available
to the chemist for the purification of solids. Additional procedures can be incorporated into
the recrystallisation process to remove impurities. These include filtration to remove
undissolved solids and adsorption to remove highly polar impurities.
Recrystallisation depends on the differential solubility of a substance in a hot and cold
solvent. It is desirable that the solubility of the substance be high in the hot solvent and low in
the cold solvent to facilitate the recovery of the starting material. The solution remaining after
crystals have deposited is known as the mother liquor. The proper choice of solvent is critical
and may require trial tests with small quantities of the material in a variety of solvents or
solvent pairs (combinations of two solvents)
Recrystallisation procedures
The solvent, or solvent pair, to be used in the recrystallisation of a substance is
chosen in the following manner. A small amount of the substance is placed in a small
test tube and a few drops of solvent are added. The test tube is gently heated to see if the
sample dissolves in the heated solvent. In general, one should first use a nonpolar
solvent, for example, hexane or petroleum ether. If the sample does not dissolve, try
using a more polar solvent such as ethanol or acetone. Should the sample completely
dissolve in any solvent, chill the solution to see whether crystals will form (sometimes it
is necessary to chill the solution using a Dry Ice-acetone bath in order to cause
crystallisation). If no crystals appear, the material is too soluble in that solvent, and that
solvent should not be used for the recrystallisation. If no single solvent provides suitable
results, a mixture of two solvents can be employed, one of the solvents being a good
solvent for the sample, and the other being a poor solvent for the sample. The sample is
first dissolved in the solvent in which the sample is most soluble, and then small
portions of the other solvent are added until a cloudiness is formed upon addition of the
second solvent. A small amount of the better solvent is added to remove the cloudiness,
and the solution is allowed to cool. The correct proportion of the two solvents must be
determined by trial and error. Once the proper solvent has been chosen, the remainder of
the sample is recrystallised.
For gram- or multigram-scale recrystallisations, the material to be recrystallised
is placed in a suitable container such as an Erlenmeyer flask.
1) Traducir la sección del texto que se indica.
2) Decidir si estas afirmaciones, RELACIONADAS CON EL TEXTO
TRADUCIDO, son verdaderas o falsas.
a) Para seleccionar el solvente más adecuado, se puede trabajar con el total
de la muestra
b) Al seleccionar el solvente más adecuado se empieza a probar con los más
polares.
c) Cuando con uno solo de los solventes no se logran los resultados deseados
se recurre al uso de dos solventes
d) Si se usan dos solventes, la muestra se disuelve primero en aquel en el que
es menos soluble.
e) Existe una fórmula precisa que permite calcular las proporciones en que
deben agregarse los dos solventes.
3) Las siguientes preguntas se refieren a las secciones QUE NO ESTÁN
INCLUÍDAS EN LA TRADUCCIÓN del texto. Respóndalas.
a)
b)
c)
d)
e)
f)
g)
¿Por qué se produce el proceso de cristalización?
¿Para qué sirve este proceso?
¿Con qué otros métodos puede combinarse y para qué se recurre a ellos?
¿Cuál es el fundamento del proceso de recristalización?
¿Qué se define en el texto como “mother liquid”
¿Cómo se elige el solvente más adecuado?
¿Cuándo se utiliza el carbón activado en este tipo de procesos?
3) Air Pollution and Climate
While acid rain and acid cloud or fog water can significantly alter the structure and
function of various compounds of terrestrial ecosystems, these may be simultaneously
stressed by a variety of other pollutants, such as ozone, toxic metals, hydrocarbons and
dry deposited particles, the common source for many of these air pollutants being the
combustion of fossil fuels.
Because of the relatively recent recognition of this diversity of air pollutants and
their interactions with terrestrial ecosystems, we have suggested that regional air
pollution is in reality more severe than it appeared to be some 20 years ago when acid
rain was discovered and was the primary regional air pollutant of concern. It was only
during these past 20 years that we became aware of the diversity and severity of airpollution climates in different regions in the Earth. For example, acid cloud and fog
water are known to be widespread in North America, particularly in the north-eastern
US.
Although ozone, like acid rain, was initially considered to be a problem with only
local dimensions, it is now clear that ozone damage to crops and natural vegetation is
widespread throughout Europe and North America. Increased dosages of ozone have
been shown to cause visible damage to plants and to reduce net photosynthesis in tree
seedlings in controlled chamber experiments. Other studies have shown statistically
significant reductions in net photosynthesis and growth of tree seedlings from ambient
ozone concentrations in the eastern US. Apparently, these ambient levels of ozone
currently may have deleterious effects on native trees showing no visible symptoms
such as stippling.
Yet long-term records of ozone concentration in the lower atmosphere are rare,
average concentrations in some rural areas of Europe appear to have increased during
the last two decades. The widely held view that ozone concentrations will peak during
the daytime hours may not hold for summits of mountains where vegetation damage is
often the most severe. For example, if we measure ozone concentrations at 1900 meters
mean sea level, these may frequently remain high throughout the day and night during
the summer, whereas at a lower elevation the diurnal pattern is different. Because ozone
concentrations are higher at higher elevations, if total ozone stress to plants were
measured, it should be more severe there than at sea level.
1) Traduzca el texto
2) Responda las siguientes preguntas.
a) ¿Cuáles son, específicamente, los efectos perjudiciales producidos por el
incremento de ozono en la vegetación?
b) ¿Bajo qué condiciones el daño debido al ozono sería mayor?
c) ¿De dónde provienen mayoritariamente los contaminantes del aire?
d) ¿En qué sentido ha cambiado la visión de esta problemática en los últimos 20 años?
3) De acuerdo con el texto, seleccione la opción correcta:
a) El texto pone énfasis principalmente en la problemática de la contaminación debida
a un grupo de contaminantes/ la lluvia ácida/ un tóxico en particular.
b) El texto plantea el tema de la contaminación de los ecosistemas terrestres como una
situación actualmente más controlable/ más compleja/ más incontrolable que hace
20 años atrás.
c) El texto pone en duda/ expone/ clasifica las causas de la contaminación del aire.
d) El texto generaliza/ compara/ especifica la acción del ozono en los ecosistemas
terrestres.
4) I - Diga si los siguientes enunciados son V o F. Corrija los falsos.
a) El ozono en particular, como contaminante, se ha propagado a lo largo de Europa
y América del Norte y se ha demostrado que su incremento ha causado daños
visibles y no visibles en la vegetación.
b) Varios contaminantes del aire, muchos de ellos provenientes de la combustión de
restos de combustibles, alteran a los ecosistemas terrestres porque actúan en forma
simultánea.
c) Durante las últimas décadas se ha incrementado el nivel de ozono a nivel mundial y
se ha demostrado que el daño producido en la vegetación es mayor a nivel del mar,
donde la concentración de este tóxico es mayor.
d) Durante mucho tiempo se desdeñó el efecto de otros contaminantes frente al de la
lluvia ácida. Ahora todos los contaminantes han dejado de considerarse como un
problema de índole local.
III- Ordene los párrafos verdaderos y los corregidos según se corresponda con el
texto de modo que quede conformado un resumen del mismo.