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Many dangerous microbes co-opt their host’s own molecular structures.

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Many dangerous microbes co-opt their host’s own molecular structures.  [#permalink]

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Many dangerous microbes co-opt their host’s own molecular structures. For example, Shigella flexneri is a rod-shaped bacterium that causes severe intestinal discomfort in humans. Shigella contains a gene called IcsA that allows it to appropriate actin filaments inside the host’s infected cell. Actin is normally used to provide structure and form to the cell, but the microbe forms the fibers into a propulsive tail that moves it freely from cell to cell. To appropriate the actin, Shigella sticks to the epithelial cells of the intestinal lining. Once there,it signals the epithelial cell to alter its own shape and pulls the microbe inside.Once Shigella is ensconced within the cytoplasm, it begins replicating. The replicants can then make use of the IcsA gene and create their own tails from the cell’s actin, spreading the infection to other cells. Thus, the bacterium bypasses the blood and lymph systems entirely, which allows it to avoid alerting the body’s immune system.

Researchers tested the IcsA hypothesis by transferring the gene into E. coli bacteria and then placing the bacteria inside host cells. The organisms formed actin tails and began behaving much as the Shigella bacteria did. Such microbes as Listeria monocytogenes also co-opt host actin,though a different gene is involved in the process.


1. It can be inferred from the passage that which of the following is true of the blood and lymph systems?

A. The blood and lymph systems are in some way linked to the immune system.
B. The blood and lymph systems are not able to overcome most bacterial infections.
C. The blood and lymph systems are used by IcsA genes to obtain actin for the creation of propulsion tails.
D. The blood and lymph systems signal noninfected epithelial cells to deny actin filaments to intrusive microbes.
E. The blood and lymph systems will be alerted to the presence of a Shigella flexneri infection when a microbe infects a white blood cell.


2. According to the author, what happens after a Shigella flexneri microbe enters a host cell?

A. The microbe depletes the nutrients in the cytoplasm and creates a replica of the original cell.
B. The microbe duplicates itself, and the duplicates form actin tails and spread to other cells.
C. After using the IcsA gene to signal to the invaded cell, the microbe spreads through the cellular lining.
D. By avoiding the immune system, the microbe spreads quickly through the blood stream.
E. The microbe first develops a propulsive tail out of actin, then co-opts the host's molecular form.



3. According to the passage, the IcsA gene is believed to control the development of actin tails for which of the following reasons?
I. The formation of actin tails cannot be attributed to any other cellular structure associated with Shigella flexneri.
II. Experiments have shown that when IcsA genes are transferred into E. coli, they develop actin tails.
III. Shigella flexneri without the IcsA gene do not grow tails formed from actin filaments.

A. I only
B. II only
C. I and II only
D. I and III only
E. II and III only



Originally posted by NickHalden on 19 Jul 2015, 12:31.
Last edited by SajjadAhmad on 26 Sep 2019, 00:47, edited 4 times in total.
Updated - Complete topic (665).
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Re: Many dangerous microbes co-opt their host’s own molecular structures.  [#permalink]

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New post 31 Oct 2018, 16:46
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Updated answer for Q3 to B.

Question Explanation


The phrase According to the passage indicates that this is a retrieval question. The task of the question is indicated by the phrase which of the following. The subject of the question is reasons that the IcsA gene is believed to control the development of actin tails. In order to answer the question, determine what the passage states about the subject and evaluate the Roman Numeral options, eliminating any choice which does not reflect the correct set of true options. According to the passage, The replicants can then make use of the IcsA gene and create their own tails from the cell’s actin, spreading the infection to other cells. The passage continues to state that Researchers tested the IcsA hypothesis and that The organisms formed actin tails and began behaving much as the Shigella bacteria did.

Choice A: No. The statement in the passage that Shigella contains a gene called IcsA that allows it to appropriate actin filaments may make Roman Numeral I seem appealing. However, the word cannot is too extreme to be supported by the text, which does not rule out other possible causes for the formation of actin tails.

Choice B: Correct. The second paragraph states that researchers tested the IcsA hypothesis by transferring the gene into E. coli and that the organisms formed actin tails and began behaving much as the Shigella bacteria did. Roman Numeral II is supported.

Choice C: No. Roman Numeral II is supported, but not Roman Numeral I. The statement in the passage that Shigella contains a gene called IcsA that allows it to appropriate actin filaments may make Roman Numeral I seem appealing. However, the word cannot is too extreme to be supported by the text, which does not rule out other possible causes for the formation of actin tails. Eliminate this choice because it relies on Roman Numeral I.

Choice D: No. Neither Roman Numeral I nor Roman nNmeral III are supported. The statement in the passage that Shigella contains a gene called IcsA that allows it to appropriate actin filaments may make Roman Numeral I seem appealing. However, the word cannot is too extreme to be supported by the text, which does not rule out other possible causes for the formation of actin tails. The statement in the passage that Shigella contains a gene called IcsA that allows it to appropriate actin filaments may make Roman Numeral III seem appealing. However, the phrase do not is too extreme to be supported by the text. While it may be true that Shigella without the IcsA gene would be unable to grow tails, the passage does not confirm that possibility.

Choice E: No. Roman Numeral II is supported, but not Roman Numeral III. The statement in the passage that Shigella contains a gene called IcsA that allows it to appropriate actin filaments may make Roman Numeral III seem appealing. However, the phrase do not is too extreme to be supported by the text. While it may be true that Shigella without the IcsA gene would be unable to grow tails, the passage does not confirm that possibility. Eliminate this choice because it relies on Roman Numeral III.

The correct answer is choice B.
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Re: Many dangerous microbes co-opt their host’s own molecular structures.  [#permalink]

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New post 22 May 2019, 04:04
Can someone please explain Q2? Thanks!
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Re: Many dangerous microbes co-opt their host’s own molecular structures.  [#permalink]

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New post 30 May 2019, 07:46
GittinGud wrote:
Can someone please explain Q2? Thanks!


Many dangerous microbes co-opt their host’s own molecular structures. For example, Shigella flexneri is a rod-shaped bacterium that causes severe intestinal discomfort in humans. Shigella contains a gene called IcsA that allows it to appropriate actin filaments inside the host’s infected cell. Actin is normally used to provide structure and form to the cell, but the microbe forms the fibers into a propulsive tail that moves it freely from cell to cell. To appropriate the actin, Shigella sticks to the epithelial cells of the intestinal lining. Once there,it signals the epithelial cell to alter its own shape and pulls the microbe inside.Once Shigella is ensconced within the cytoplasm, it begins replicating. The replicants can then make use of the IcsA gene and create their own tails from the cell’s actin, spreading the infection to other cells. Thus, the bacterium bypasses the blood and lymph systems entirely, which allows it to avoid alerting the body’s immune system.

Researchers tested the IcsA hypothesis by transferring the gene into E. coli bacteria and then placing the bacteria inside host cells. The organisms formed actin tails and began behaving much as the Shigella bacteria did. Such microbes as Listeria monocytogenes also co-opt host actin,though a different gene is involved in the process

see this line in the passage it will clear your doubt
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Re: Many dangerous microbes co-opt their host’s own molecular structures.  [#permalink]

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New post 19 Jun 2019, 08:35
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For Q.2...I amm confused between (b) and (e)...I think both gives a correct order of actions ..
Plz help clarify
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Re: Many dangerous microbes co-opt their host’s own molecular structures.  [#permalink]

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New post 19 Jun 2019, 22:28
Debashis Roy wrote:
GMATNinja VeritasKarishma
For Q.2...I amm confused between (b) and (e)...I think both gives a correct order of actions ..
Plz help clarify



Shigella contains a gene called IcsA that allows it to appropriate actin filaments inside the host’s infected cell. - Gene IcsA allows Shigella to take the host's actin.

Actin is normally used to provide structure and form to the cell, but the microbe forms the fibers into a propulsive tail that moves it freely from cell to cell. - For what does Shigella use actin? To form a tail to move around freely

To appropriate the actin, Shigella sticks to the epithelial cells of the intestinal lining. - How does Shigella take actin? To take actin, it sticks to epithelial cells.

Once there,it signals the epithelial cell to alter its own shape and pulls the microbe inside. - It signals epithelial cells to pull it inside.

Once Shigella is ensconced within the cytoplasm, it begins replicating. - Once Shigella is inside, it starts replicating

The replicants can then make use of the IcsA gene and create their own tails from the cell’s actin, spreading the infection to other cells. - The replicants use IcsA gene to create tails from actin and spread the infection.

According to the author, what happens after a Shigella flexneri microbe enters a host cell?


B. The microbe duplicates itself, and the duplicates form actin tails and spread to other cells.

Exactly what is given in the passage.

E. The microbe first develops a propulsive tail out of actin, then co-opts the host's molecular form.

Not given that the microbe first develops a tail. The microbe sticks to epithelial cells, enter inside, replicate and then duplicates use actin to develop tails.

Answer (B)
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Re: Many dangerous microbes co-opt their host’s own molecular structures.  [#permalink]

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New post 19 Jun 2019, 22:32
Giampa wrote:
soumya170293 wrote:
plz explain the question no 3 ??
though (ii) has been mentioned but I didn't get whether (i) is in the RC ?

Same problem! Someone can help me?


3. According to the passage, the IcsA gene is believed to control the development of actin tails for which of the following reasons?


Why do we think that gene IcsA controls the development of actin tails? What proof do we have as per the passage?

Researchers tested the IcsA hypothesis by transferring the gene into E. coli bacteria and then placing the bacteria inside host cells. The organisms formed actin tails and began behaving much as the Shigella bacteria did. - IcsA was transferred to E. coli and it started developing actin tails.

Such microbes as Listeria monocytogenes also co-opt host actin,though a different gene is involved in the process. - Some other microbes use different genes to use actin.


I. The formation of actin tails cannot be attributed to any other cellular structure associated with Shigella flexneri. - Not given in passage.
II. Experiments have shown that when IcsA genes are transferred into E. coli, they develop actin tails. - True as per passage
III. Shigella flexneri without the IcsA gene do not grow tails formed from actin filaments. - Not given in passage

Answer (B)
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Re: Many dangerous microbes co-opt their host’s own molecular structures.  [#permalink]

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New post 20 Jun 2019, 01:54
Please explain question 1
I am getting choice e
The blood and lymph system will be alerted therefore the bacterium is bypassing it?
Is my thinking wrong ?

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Re: Many dangerous microbes co-opt their host’s own molecular structures.  [#permalink]

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New post 15 Sep 2019, 12:39
blueshores Answer to Ques 1:-

Choice A: Correct. The last sentence of the first paragraph states that the bacterium bypasses the blood and lymph systems entirely, which allows it to avoid alerting the body’s immune system. This shows a link between the blood and lymph systems and the immune system.

Choice E: No. This answer choice uses outside knowledge to be appealing. The phrase infects a white blood cell in the answer choice is appealing to anyone with prior knowledge of white blood cells and the immune system. However, the passage states that the bacterium bypasses the blood and lymph systems, and supports nothing about white blood cells.
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Re: Many dangerous microbes co-opt their host’s own molecular structures.   [#permalink] 15 Sep 2019, 12:39
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