#1 - Main Point

[Administrator]

Complete Question Explanation
(See the complete passage discussion here: lsat/viewtopic.php?t=13636)

The correct answer choice is (B)

Answer choice (A): Although it is accurate to say that the mechanism by which prions reproduce themselves is not yet completely understood, the author does not confirm the first part of this answer choice, which does not express the main point of the passage; it should thus be ruled out of contention in response to this Main Point question.

Answer choice (B): This is the correct answer choice. As discussed above, the author’s main point is to discuss prions, a new kind of pathogen made up, surprisingly, of protein rather than standard DNA or RNA associated with the four previously known infection-causing agents.

Answer choice (C): In the last paragraph, the author mentions that similar protein malformation might take place in other conditions, but does not go so far as to assert that this applies to “most” other neurological conditions. Since this choice doesn’t even pass the Fact Test, it cannot be the correct answer choice to this Main Point question.

Answer choice (D): At the beginning of the last paragraph, the author says that the scientific community was skeptical regarding the link between prions and CJD, but then goes on to say that subsequent research has supported the notion that prions are a new class of pathogen. Since this choice discusses the skepticism about that link in the present tense, with the implication that it continues, this answer is not supported by the information in the passage and should be ruled out of contention.

Answer choice (E): The passage does describe the prions’ general approach to reproduction, and the author mentions that they lack nucleic acid, but this is not the main point of the passage, so it cannot be the correct response to this Main Point question.

[harvoolio]

I did not select this answer because of the last three words of "without genetic material" because I did not think the passage had established this.

On line 22 it reads "the isolation of a disease agent lacking nucleic acid and consisting mainly if not exclusively of protein."

I missed the comma on line 8 which might have made a difference but reads "regulate their other life processes by means of genetic material, composed of nucleic acid (DNA or RNA).

Without a science background, I had incorrectly assumed that what had been established is that the new prion did not reproduce with nucleic acid, but could have reproduced with some other genetic material, just not nucleic acid.

Or is it lines 33 to 36 that has the answer. Thanks.

[Malila Robinson]

Hi Harvoolio,
The thing to focus on is that the passage repeatedly says that the prions reproduce themselves, meaning they apparently do not need the intervention of something like genetic material in order to reproduce.

- "they possess the capability of converting their structures into a (30) dangerous abnormal shape."

-"Prions exhibiting this abnormal conformation were found to have infectious properties and the ability to reproduce themselves in an unexpected way, by initiating a chain reaction that induces normally shaped prions to transform (35) themselves on contact, one after another, into the abnormal, pathogenic conformation."

-"And in the absence of any effective therapy for preventing the cascade process by which affected prions reproduce (45) themselves, CJD is inevitably fatal"

-"and the exact mechanisms by which prions reproduce themselves and cause cellular destruction have yet to (60) be completely understood."
Hope that helps!
-Malila

[harvoolio]

Thanks, but maybe I did not explain my question well enough.

Had answer (B) been written as "Research into the cause of CJD has uncovered a deadly class of protein pathogens uniquely capable of reproducing themselves without nucleic acid." or "Research into the cause of CJD has uncovered a deadly class of protein pathogens uniquely capable of reproducing themselves without something like genetic material.", I would have selected it for all of the reasons you wrote.

But the answer reads "Research into the cause of CJD has uncovered a deadly class of protein pathogens uniquely capable of reproducing themselves without genetic material."

Where has "without genetic material" been conclusively established?

Thanks.

[Malila Robinson]

Hi Harvoolio,
Yes, the segments that I quoted show that the prions are reproducing themselves (not using outside genetic material). And the passage says that prions are protein, not nucleic acid- DNA/RNA which are genetic materials. (see the quoted material below, with the important parts in bold for emphasis)

"The only agents believed until recently to be responsible for infections—viruses, bacteria, fungi, and parasites—reproduce and regulate their other life processes by means of genetic material, composed of nucleic acid (DNA or RNA). It was thus (10) widely assumed that all pathogens contain such genetic material in their cellular structure. This assumption has been challenged, however, by scientists seeking to identify the pathogen that causes Creutzfeldt-Jakob disease (CJD), a degenerative (15) form of dementia in humans. CJD causes the brain to become riddled with tiny holes, like a sponge (evidence of extensive nerve cell death). Its symptoms include impaired muscle control, loss of mental acuity, memory loss, and chronic insomnia. Extensive experiments (20) aimed at identifying the pathogen responsible for CJD have led surprisingly to the isolation of a disease agent lacking nucleic acid and consisting mainly, if not exclusively, of protein. Researchers coined the term “prion” for this new type of protein pathogen. (25)"

Hope this helps,
-Malila

[harvoolio]

Malila,

Let me ask this another way.

Does the phrase "composed of" means that the parts represent an exhaustive list? If the answer is yes, then I understand everything. If the answer is no, I do not.

Because, if the answer is yes, then the phrase "genetic material, composed of nucleic acid (DNA or RNA)" means knowing that something lack nucleic acid is sufficient to know it lacks genetic material. If the answer is no, then the phrase "genetic material, composed of nucleic acid (DNA or RNA)" means knowing that something lack nucleic acid is insufficient to know it lacks genetic material.

Thanks,
Michael

[Francis O'Rourke]

Hi Harvoolio,

You are asking a very interesting question about this author's meaning here, but ultimately you are being a bit too strict with your reading. Lines 5 - 9 do not necessarily rule out the existence of any other kind of genetic material. The author of this passage likely intended that to be a definitive list, but you are right that it is in itself worded it in such a way that the strictest reading would allow for the existence of a protein genetic material.

However, you have to know what you are reading.

One of the most common ways to interpret a sentence with the structure "[specialized term], [explanatory phrase]" is to read that explanatory phrase as a definition. On this reading, the definition of "genetic material" would be "that which is composed of nucleic acid (DNA or RNA)."

Furthermore, it often happens that a specialist will assume some familiarity with their field after using the same terms for their entire career. It happens to be the case that many biology passages will equate "genetic material" with "DNA or RNA," and will not fully explain that proteins are distinct from genes.

It is still possible, as you point out, that the author is merely giving us examples of the kinds of genetic material which known pathogens use to reproduce in the sentence in question. If this were a legal text, there may be questions to be had about the ambiguity here. The author of the passage though is not as clear as the writers of the logical reasoning questions or of many of the legal reading passages that you will encounter.

You should expect some nonlegal writers to leave ambiguities in their writing. In this case, we must read holistically and ask ourselves which interpretation is more likely. If proteins are just another type of genetic material, why would the author describe prions as a "entirely new class of infectious pathogens"?

Furthermore, the author describes genetic material as a tool or means used by something else to reproduce. The genetic material copies itself to reproduce an organism. As Malila wrote above, the prion proteins are clearly not using a tool, but are rather reproducing themselves without resorting to a separate entity to intervene in reproduction. This does not sound like the roll of genetic materials described by the author.

All of this is irrelevant to answering the question though. You may be unsure of the veracity of the phrase "genetic material" in answer choice (B). In this case, leave it alone, treat it as possibly correct, and focus on the other parts of the answers which you can conclusively prove or disprove from the reading.

I hope that this helps, but let me know if you have any further questions!

[harvoolio]

Thank you for your detailed response which I understand. Especially for a Main Point question the ambiguity is non-material. I should have been able to eliminate the other 4 answer choices.

But for applicability to other questions, you say the author intended "composed of" to be "definitive". So, are you using "definitive" interchangeably with "exhaustive" and the two words are synonyms to you? In other words "composed of" is "definitive" and means considering all elements and fully comprehensive? This might seem like nitpicking, but often LSAT questions hinge on precisely understanding terms like "composed of" which I am still unclear (for other questions) whether I am to read this as an exhaustive or non-exhaustive list.

Thanks again.

Also, science passages are the bane of my existence. I just finished your excellent Reading Comprehension Bible and answered 93% of Non-Science passage questions correctly, but only 82% of Science passage questions correctly (89% overall).

[Francis O'Rourke]

Definite is a synonym of exhaustive, and that is the way that I was using the word. In my mind a "definitive list" is more natural to say than an "exhaustive list" is, but I'm not sure which one is more common. Although we often think of "defining" merely as "explaining," I use the word "define" in its original sense of "showing the edges or boundaries of."

If you come across the word "definitely" on the LSAT, you should recognize that the author may use it in the sense of explaining or limiting.

[harvoolio]

Thanks again Francis. (23 out of 27 on my latest diagnostic so hopefully one day I can definitively answer all questions correctly).