PSAT Reading Practice Test 48: Science: Fungi

Questions 1-9 refer to the following information.

With good reason, biologists have frequently described fungi as the "forgotten kingdom."
Despite demonstrating a diversity and evolutionary resilience to rival plants and animals
alike, for many of us, our day-to-day familiarity with fungi reaches little further than to a
handful of domesticated mushrooms, and perhaps the Penicillium molds that imbue blue
05cheese with their distinctive color and smell. In reality, fungi are all around us, and contribute
biochemically to a remarkable variety of both natural and artificial processes: from the vital
decomposition of organic matter commonly described as "rotting" to the yeast-mediated fermentation
of polysaccharides into ethanol and gaseous carbon dioxide which allows a bak-
er's bread to rise. Even so, perhaps due to their obscure, soil-dwelling lifestyles, the manifold
10functions that fungi execute in our lives are more often than not inconspicuous, and all too
easily overlooked.
The health sciences especially are rife with novel applications for mycology (that is, the
branch of biology emphasizing fungi). Famously, the first commercially available antibiotics
capable of curing streptococcal and staphylococcal infections were discovered quite by
15accident when Scottish scientist Alexander Fleming noticed how the growth of a staphylococcus
culture had been drastically inhibited following its contamination with a Penicillium
chrysogenum mold. Notably, the unique mechanism by which this inhibitory effect is accomplished
has since led to the development of not one but three distinct classes of antimicrobial
medications-penicillins, cephalosporins, and beta-lactamase inhibitors-and accelerated
20a set of fascinating genetic mutations which confer antibiotic resistance among strains of
bacteria.
In penicillins and cephalosporins, the so-called "beta-lactam ring" is known to be the
principle structure responsible for their antimicrobial properties. This ring binds avidly to
specialized cross-linking proteins found within the peptidoglycan layer of bacterial cell walls,
25subsequently blocking a bacterium's attempts at reproduction, as well as the replication of
its intracellular organelles. As it is not found naturally within the cells of animals, plants, or
fungi, peptidoglycan polymers are highly peculiar to bacteria, and antimicrobial agents targeting
peptidoglycan possess a very low potential for toxic cross-reactivity with other types
of cells.
30Even into the 21st century, beta-lactam compounds still comprise more than half of all
antibiotics prescribed worldwide, and it is widely believed that their pervasive usage has
helped to promote the novel synthesis of beta-lactamases among a wide array of common
pathogenic bacterial species. To clarify, beta-lactamases are a class of enzymes capable of
hydrolyzing the beta-lactam ring, and are often secreted in the presence of antibiotics. While
35these enzymes are nigh ubiquitous among bacteria today, prior to the commercial availability
of penicillin, their endogenous synthesis was limited to a fairly small number of gram-negative
organisms. The startling rapidity with which bacteria have developed resistance against
beta-lactams may have far reaching implications for the health of human populations in the
future.
40Although penicillin is perhaps the most memorable example, it is hardly the only contribution
fungi have made to improving human health. In recent years, a number of medicinally
significant fungal isolates have emerged to treat not just infection, but metabolic, immuno-
logic, and neoplastic diseases as well. Of particular note, 3-hydroxy-3-methylglutaryl-CoA
reductase inhibitors-more commonly called "statins"-are considered the first-line phar-
45macological therapy for hypercholesterolemia, and are the only cholesterol-lowering class
of medications that have been proven in peer-reviewed longitudinal studies to lower an
individual's risk of major cardiovascular disease. Mechanistically, rather than blocking the
absorption of dietary cholesterol or enhancing its excretion, statins work to reduce the de
novo biosynthesis of cholesterol molecules in the body by inhibiting the rate-limiting enzyme
50in its anabolic pathway.
It would not be overstating the matter to say that statins have transformed the treatment
of both acquired and congenital cholesterol-related diseases. But what's more, the first generation
of statins was discovered, oddly enough, by Japanese scientist Akira Endo during
his research into the antimicrobial properties of the mold Penicillium citrinum. Not unlike
55Alexander Fleming one-half century earlier, Endo serendipitously discovered yet another
compound from this curious genus of fungi destined to do no less than revolutionize the
medical maintenance of human health. One must wonder, therefore, what more we stand to
learn from fungi, and what still-greater mysteries they may yet be concealing in the soil.