Mcat экзамен пример

Resistance to antibiotics in clinical isolates of gram-negative and gram-positive bacteria is usually mediated by the presence of various enzymes that modify the antibiotic so that it can no longer interact with its target in the cell. The β-lactamases hydrolyze the penicillins and cephalosporins, chloramphenicol acetyltransferase acetylates chloramphenicol, and nine enzymes acetylate, phosphorylate, or adenylylate the aminoglycoside antibiotics.

 
The genetic loci coding for these enzymes are usually located on extrachromosomal elements, such as the R(antibiotic resistance)-factors in gram-negative bacteria. Since these genes are not normal chromosomal components of the resistant strains, there has been considerable speculation as to their origin.

 
Molecular studies have shown that R-factors consist of two parts that are reversibly dissociable. These are the resistance transfer factor (RTF), and the r-determinants, genes that determine resistance to antibiotics. It has been hypothesized that r-determinants exist somewhere in nature as chromosomal genes and that they are «picked-up» by bacteria to form R-factors. The question is, where do the r-determinants originate?

 
A search was initiated in the actinomycetes for aminoglycoside-modifying enzymes like those that have been characterized in strains carrying R-factors (R+) in the belief that this might represent the r-determinant gene pool. The actinomycetes are a group of rod-shaped organisms that were once thought to be intermediates between bacteria and fungi. However, careful examination of their cellular dimensions, their cytology, and their genetics place them among the bacteria.

 
Table 1   Aminoglycoside acetylating, phosphorylating, and adenylylating enzymes in actinomycetes; (+) means enzyme activity was detected, (-) means no enzyme activity was detected.

Adapted from Benveniste, R., Davies, J. Aminoglycoside Antibiotic-Inactivating Enzymes in Actinomycetes Similar to Those Present in Clinical Isolates of Antibiotic-Resistant Bacteria Proc. Nat. Acad. Sci. USA Vol. 70, No. 8, pp. 2276-2280

Resistance to antibiotics in clinical isolates of gram-negative and gram-positive bacteria is usually mediated by the presence of various enzymes that modify the antibiotic so that it can no longer interact with its target in the cell. The β-lactamases hydrolyze the penicillins and cephalosporins, chloramphenicol acetyltransferase acetylates chloramphenicol, and nine enzymes acetylate, phosphorylate, or adenylylate the aminoglycoside antibiotics.

 
The genetic loci coding for these enzymes are usually located on extrachromosomal elements, such as the R(antibiotic resistance)-factors in gram-negative bacteria. Since these genes are not normal chromosomal components of the resistant strains, there has been considerable speculation as to their origin.

 
Molecular studies have shown that R-factors consist of two parts that are reversibly dissociable. These are the resistance transfer factor (RTF), and the r-determinants, genes that determine resistance to antibiotics. It has been hypothesized that r-determinants exist somewhere in nature as chromosomal genes and that they are «picked-up» by bacteria to form R-factors. The question is, where do the r-determinants originate?

 
A search was initiated in the actinomycetes for aminoglycoside-modifying enzymes like those that have been characterized in strains carrying R-factors (R+) in the belief that this might represent the r-determinant gene pool. The actinomycetes are a group of rod-shaped organisms that were once thought to be intermediates between bacteria and fungi. However, careful examination of their cellular dimensions, their cytology, and their genetics place them among the bacteria.

 
Table 1   Aminoglycoside acetylating, phosphorylating, and adenylylating enzymes in actinomycetes; (+) means enzyme activity was detected, (-) means no enzyme activity was detected.

Adapted from Benveniste, R., Davies, J. Aminoglycoside Antibiotic-Inactivating Enzymes in Actinomycetes Similar to Those Present in Clinical Isolates of Antibiotic-Resistant Bacteria Proc. Nat. Acad. Sci. USA Vol. 70, No. 8, pp. 2276-2280

Resistance to antibiotics in clinical isolates of gram-negative and gram-positive bacteria is usually mediated by the presence of various enzymes that modify the antibiotic so that it can no longer interact with its target in the cell. The β-lactamases hydrolyze the penicillins and cephalosporins, chloramphenicol acetyltransferase acetylates chloramphenicol, and nine enzymes acetylate, phosphorylate, or adenylylate the aminoglycoside antibiotics.

 
The genetic loci coding for these enzymes are usually located on extrachromosomal elements, such as the R(antibiotic resistance)-factors in gram-negative bacteria. Since these genes are not normal chromosomal components of the resistant strains, there has been considerable speculation as to their origin.

 
Molecular studies have shown that R-factors consist of two parts that are reversibly dissociable. These are the resistance transfer factor (RTF), and the r-determinants, genes that determine resistance to antibiotics. It has been hypothesized that r-determinants exist somewhere in nature as chromosomal genes and that they are «picked-up» by bacteria to form R-factors. The question is, where do the r-determinants originate?

 
A search was initiated in the actinomycetes for aminoglycoside-modifying enzymes like those that have been characterized in strains carrying R-factors (R+) in the belief that this might represent the r-determinant gene pool. The actinomycetes are a group of rod-shaped organisms that were once thought to be intermediates between bacteria and fungi. However, careful examination of their cellular dimensions, their cytology, and their genetics place them among the bacteria.

 
Table 1   Aminoglycoside acetylating, phosphorylating, and adenylylating enzymes in actinomycetes; (+) means enzyme activity was detected, (-) means no enzyme activity was detected.

Adapted from Benveniste, R., Davies, J. Aminoglycoside Antibiotic-Inactivating Enzymes in Actinomycetes Similar to Those Present in Clinical Isolates of Antibiotic-Resistant Bacteria Proc. Nat. Acad. Sci. USA Vol. 70, No. 8, pp. 2276-2280

The term «baby boomer» is used to describe anyone born in the United States between 1946 and 1964. As of 2011, baby boomers have been driving the growth of the senior citizen population, and by 2029, when all of the baby boomers are 65 years or older, it is projected that more than 20 percent of the U.S. population will be over the age of 65. By 2056, the population 65 years and over is projected to become larger than the population under 18 years.

 
Figure 1 shows the age and sex structure for the population of the United States between 1945 and 2012. The bulge in the pyramids are shaded in gray and represent the baby boomer cohort.

 
 
 
Figure 1 Age and Sex Structure of the Population for the United States: 1945 to 2012 (Numbers in millions)

 
The dependency ratio of a population can be defined as the ratio of the number of «dependent» members of a population to the number of «productive» members of the same population. In Western societies such as the United States, demographers measure the dependency ratio according to the following formula:
 
(Equation 1)

 
In the United States, the total dependency ratio increased steadily from 1945 to 1964, peaking at about 0.8 in 1964. After the baby boomers entered the workforce, the ratio decreased slowly until 2010, when it reached its nadir at 0.59. The projected dependency ratio for 2060 is 0.75, and this is mostly due to the large effect that the baby boomer generation will have.

 
Source: Adapted from Colby, Ortman, The Baby Boom Cohort in the United States: 2012 to 2060; United States Census. Issued May 2014 P25-1141

The term «baby boomer» is used to describe anyone born in the United States between 1946 and 1964. As of 2011, baby boomers have been driving the growth of the senior citizen population, and by 2029, when all of the baby boomers are 65 years or older, it is projected that more than 20 percent of the U.S. population will be over the age of 65. By 2056, the population 65 years and over is projected to become larger than the population under 18 years.

 
Figure 1 shows the age and sex structure for the population of the United States between 1945 and 2012. The bulge in the pyramids are shaded in gray and represent the baby boomer cohort.

 
 
 
Figure 1 Age and Sex Structure of the Population for the United States: 1945 to 2012 (Numbers in millions)

 
The dependency ratio of a population can be defined as the ratio of the number of «dependent» members of a population to the number of «productive» members of the same population. In Western societies such as the United States, demographers measure the dependency ratio according to the following formula:
 
(Equation 1)

 
In the United States, the total dependency ratio increased steadily from 1945 to 1964, peaking at about 0.8 in 1964. After the baby boomers entered the workforce, the ratio decreased slowly until 2010, when it reached its nadir at 0.59. The projected dependency ratio for 2060 is 0.75, and this is mostly due to the large effect that the baby boomer generation will have.

 
Source: Adapted from Colby, Ortman, The Baby Boom Cohort in the United States: 2012 to 2060; United States Census. Issued May 2014 P25-1141

Leukocyte NADPH oxidases are membrane-associated enzyme complexes that catalyze the production of superoxide (O2-1) via the one-electron reduction of dioxygen.

 
2O₂ + NADPH → 2O₂— + NADP⁺ + H⁺(Reaction 1)

 
The O2- produced by reaction 1 is an ROS (reactive oxygen species) that causes oxidative damage to biomolecules such as DNA and serves as the starting material for the production of a vast assortment of other reactive oxidants such as oxidized halogens, free radicals, and singlet oxygen.

 
Because of its reactivity, O2- has potent bactericidal effects, and when O2- is pumped into a phagosome en masse, any microbe the phagocyte has engulfed is quickly destroyed. Hence the presentation of a microbe to a phagocyte elicits the rapid consumption of O2 and production of O2-, a phenomenon known as a respiratory burst.

 
In order to quantitatively compare ROS production in neutrophils, monocytes, mast cells, and dendritic cells, a solution of 2,7-dichlorodihydrofluorescein diacetate (H2DCFDA) is prepared. H2DCFDA is a non-fluorescent, cell-permeable dye, which oxidizes to the fluorescent 2,7-dichlorofluorescein (DSF) in the presence of a strong enough oxidant (such as a ROS).

 
Two samples of each type of leukocyte are pipetted into different wells of a microplate and all eight wells are incubated with equal amounts of H2DCFDA for thirty minutes. Phorbol myristate acetate (PMA), a compound known to induce a respiratory burst, is then added to one well of each leukocyte type. Fluorescence measurements are taken for all wells zero hours (i.e. immediately), one hour, and two hours following PMA addition. The results are shown in Table 1.

Museums have always been about more than housing art, be it in the service of the work itself (how to bring out certain aesthetic qualities) or by making a broader social statement. Yet, something less obvious than simply creating a distance between observer and the observed or curating the works of a specific artist is at play. What also informs the modern museum-going experience is the ‘who’ viewing the art and what exactly that person’s expectations of the experience are.

 
For much of the 20th century—and really all of the 19th century—to enter a museum was to be in the midst of Greatness. The requisite emotion was awe; the self was no longer the center of one’s attention. It helped if museum-goers were familiar with the story of art, so that they could direct that awe appropriately. Yet, this story served an even deeper purpose, as the transformation of the museum in the last fifty years has shown. Museum-goers demanded to be edified by that story. But now that story—that the past was a series of great masters to kneel before—is itself becoming a relic. The public has changed and, so the notion goes, so too must the museum.

 
The progressive-museum-going experience has its beginnings in the end of the 19th century, and has, since then, steadily grown in the United States. The idea is not only about housing artworks under a roof but about being an agent for social change. The museum as subversive. Or, if that is too ambitious, the museum has become not so much a custodian of great art as an institution that caters to the museum goer’s experience. But if that experience has become less about art, then what has it become more about?

 
One argument is that the museum needs to be more attuned to how an individual sees him- or herself against the backdrop of Art. Spaces for easy congregation, whether at a museum café or a large open area in between statues, are addressing this need. Installation art, in which there is no art in the traditional sense, but a space created ad hoc, where the museum goer is part of the experience, is another trend highlighting a shift away from “unselfing.” Some maintain this renewed focus on the self is alarming, and point out that museums are trying to attract younger generations by offering “selfie spaces” where individuals can use smartphones to take pictures of themselves standing next to the likes of the David. This is an extreme example, given that many museums are not focused on pandering to the popular masses, and perhaps points more to how its proponents are clearly reactionary. Many of these critics insist on clinging to the traditional model, the one in which museums have become little more than bastions of stuffiness, an old-world order frozen in time, deaf to the sensibilities of a changing public.

 
What needs redefining is the simplistic dichotomy between upholding the value of Art and catering to the whims of the public. It misses the subtle dynamic of how the museum-going public both engages and disengages with conscious curatorial and structural adaptations. For instance, the public—underscoring the trend in placing the self at the center of the experience—has become more demanding of an interactive experience, not surprising given how digital technology itself is predicated on an individual-mediated response to the intake of information. One idea a museum could play with, if some have not already, is for the docent to go online, allowing the individual to “curate the experience” as she walks past works of art chosen with this end in mind. Museums might also experiment with other approaches; whether these involve classic works or collections outside of the western canon, or whether they can be described as installation art is besides the point. Saying that any of these approaches are compromised presupposes that there is only one experience. In fact, museums in the stuffy mold should still exist, but they should also be content with their diminished status.

Museums have always been about more than housing art, be it in the service of the work itself (how to bring out certain aesthetic qualities) or by making a broader social statement. Yet, something less obvious than simply creating a distance between observer and the observed or curating the works of a specific artist is at play. What also informs the modern museum-going experience is the ‘who’ viewing the art and what exactly that person’s expectations of the experience are.

 
For much of the 20th century—and really all of the 19th century—to enter a museum was to be in the midst of Greatness. The requisite emotion was awe; the self was no longer the center of one’s attention. It helped if museum-goers were familiar with the story of art, so that they could direct that awe appropriately. Yet, this story served an even deeper purpose, as the transformation of the museum in the last fifty years has shown. Museum-goers demanded to be edified by that story. But now that story—that the past was a series of great masters to kneel before—is itself becoming a relic. The public has changed and, so the notion goes, so too must the museum.

 
The progressive-museum-going experience has its beginnings in the end of the 19th century, and has, since then, steadily grown in the United States. The idea is not only about housing artworks under a roof but about being an agent for social change. The museum as subversive. Or, if that is too ambitious, the museum has become not so much a custodian of great art as an institution that caters to the museum goer’s experience. But if that experience has become less about art, then what has it become more about?

 
One argument is that the museum needs to be more attuned to how an individual sees him- or herself against the backdrop of Art. Spaces for easy congregation, whether at a museum café or a large open area in between statues, are addressing this need. Installation art, in which there is no art in the traditional sense, but a space created ad hoc, where the museum goer is part of the experience, is another trend highlighting a shift away from “unselfing.” Some maintain this renewed focus on the self is alarming, and point out that museums are trying to attract younger generations by offering “selfie spaces” where individuals can use smartphones to take pictures of themselves standing next to the likes of the David. This is an extreme example, given that many museums are not focused on pandering to the popular masses, and perhaps points more to how its proponents are clearly reactionary. Many of these critics insist on clinging to the traditional model, the one in which museums have become little more than bastions of stuffiness, an old-world order frozen in time, deaf to the sensibilities of a changing public.

 
What needs redefining is the simplistic dichotomy between upholding the value of Art and catering to the whims of the public. It misses the subtle dynamic of how the museum-going public both engages and disengages with conscious curatorial and structural adaptations. For instance, the public—underscoring the trend in placing the self at the center of the experience—has become more demanding of an interactive experience, not surprising given how digital technology itself is predicated on an individual-mediated response to the intake of information. One idea a museum could play with, if some have not already, is for the docent to go online, allowing the individual to “curate the experience” as she walks past works of art chosen with this end in mind. Museums might also experiment with other approaches; whether these involve classic works or collections outside of the western canon, or whether they can be described as installation art is besides the point. Saying that any of these approaches are compromised presupposes that there is only one experience. In fact, museums in the stuffy mold should still exist, but they should also be content with their diminished status.

Museums have always been about more than housing art, be it in the service of the work itself (how to bring out certain aesthetic qualities) or by making a broader social statement. Yet, something less obvious than simply creating a distance between observer and the observed or curating the works of a specific artist is at play. What also informs the modern museum-going experience is the ‘who’ viewing the art and what exactly that person’s expectations of the experience are.

 
For much of the 20th century—and really all of the 19th century—to enter a museum was to be in the midst of Greatness. The requisite emotion was awe; the self was no longer the center of one’s attention. It helped if museum-goers were familiar with the story of art, so that they could direct that awe appropriately. Yet, this story served an even deeper purpose, as the transformation of the museum in the last fifty years has shown. Museum-goers demanded to be edified by that story. But now that story—that the past was a series of great masters to kneel before—is itself becoming a relic. The public has changed and, so the notion goes, so too must the museum.

 
The progressive-museum-going experience has its beginnings in the end of the 19th century, and has, since then, steadily grown in the United States. The idea is not only about housing artworks under a roof but about being an agent for social change. The museum as subversive. Or, if that is too ambitious, the museum has become not so much a custodian of great art as an institution that caters to the museum goer’s experience. But if that experience has become less about art, then what has it become more about?

 
One argument is that the museum needs to be more attuned to how an individual sees him- or herself against the backdrop of Art. Spaces for easy congregation, whether at a museum café or a large open area in between statues, are addressing this need. Installation art, in which there is no art in the traditional sense, but a space created ad hoc, where the museum goer is part of the experience, is another trend highlighting a shift away from “unselfing.” Some maintain this renewed focus on the self is alarming, and point out that museums are trying to attract younger generations by offering “selfie spaces” where individuals can use smartphones to take pictures of themselves standing next to the likes of the David. This is an extreme example, given that many museums are not focused on pandering to the popular masses, and perhaps points more to how its proponents are clearly reactionary. Many of these critics insist on clinging to the traditional model, the one in which museums have become little more than bastions of stuffiness, an old-world order frozen in time, deaf to the sensibilities of a changing public.

 
What needs redefining is the simplistic dichotomy between upholding the value of Art and catering to the whims of the public. It misses the subtle dynamic of how the museum-going public both engages and disengages with conscious curatorial and structural adaptations. For instance, the public—underscoring the trend in placing the self at the center of the experience—has become more demanding of an interactive experience, not surprising given how digital technology itself is predicated on an individual-mediated response to the intake of information. One idea a museum could play with, if some have not already, is for the docent to go online, allowing the individual to “curate the experience” as she walks past works of art chosen with this end in mind. Museums might also experiment with other approaches; whether these involve classic works or collections outside of the western canon, or whether they can be described as installation art is besides the point. Saying that any of these approaches are compromised presupposes that there is only one experience. In fact, museums in the stuffy mold should still exist, but they should also be content with their diminished status.